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ce0f18f4ef868503976cb44cd33bb99ed6e7a5b0
SplitBit-Emulator/Programs/CosmOS/Source/sbfs.asm
T
Anachronaut ce0f18f4ef Refuse a directory whose last entries cannot be named as a parent 
A parent is an entry index PLUS ONE in two bytes, so entry 65535 has no
parent number: adding one wraps to zero, and zero is the root. Eight
entries to a block, so 8192 directory blocks reaches it and SplitDisk
formatted that happily.

It does not fail by refusing, which is why it was worth chasing rather than
reasoning about. Reproduced on a disk built for it: mkdir /deep/child, with
/deep at entry 65535, printed 'Made "/deep/child" as entry 0' and put child
in the ROOT. Listing /deep then showed nothing, because the search is for a
parent of 65536 and the entry carries zero - so the same mkdir succeeded
again, and again, and five entries called /child piled up in the root.
Duplicate names in one directory are the one thing rename refuses outright,
on the grounds that a search answers with whichever it meets first and the
rest can never be reached; this manufactured them one per attempt.

8191 blocks is the most, giving 65528 entries. Refused when formatting and
again when reading, in both implementations, because a disk claiming more
was made by something that never checked. On the machine only the high byte
of the count has to be looked at: anything from 0x20 up is too many.

Three checks, all of which fail with their guard removed. The machine's
disk claims the size rather than having it, so the test image is 64 blocks
that lie rather than sixteen megabytes that do not - mounting is refused at
the geometry, which is read out of block 0.
2026-08-25 23:47:02 -04:00

3168 lines
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; sbfs.asm
; Reading the SplitBit Filesystem.
;
; This belongs to CosmOS, which is the thing that needs it. Programs outside CosmOS may
; include it, and the test programs do, but when CosmOS becomes a repository of its own
; this file goes with it and anything left behind takes a copy.
;
; The other implementation of this format is SplitDisk on the host. Nothing is shared
; between them but the written specification, so anything that changes here has to change
; there in the same breath.
;
; ---- What an entry's flags mean ----
;
; 0x01 In use. A zero here is a free slot, whatever else the bytes hold.
; 0x02 A directory, which has no blocks at all.
; 0x04 A file being written and not yet committed. See sbfsSaveFile.
;
; The disk's buffer is registered as bank 3, and every block read lands there and is then
; blitted where it is wanted. The CPU never touches the buffer directly, because nothing
; can: memory a device brings is reachable only through the controller.
;
; Written by Anachronaut
#Program
; Registers the disk's buffer, reads the superblock, and checks that the disk really is
; one of ours. Q is zero if the disk is ready to be read.
sbfsMount:
INIA 0d3
OUTA 0xE3
INIA 0x20
OUTA 0xE2
INIA 0x03
OUTA 0xE8 ; RegisterBank: bank 3 is the disk's buffer.
SETD.0 SbfsBlock
RSTA
STA.0
INCD.0
STA.0 ; Block 0, the superblock.
CALL sbfsReadBlock
BRQ sbfsMountRead
RET ; The read failed, and Q says so.
sbfsMountRead:
SETD.1 SbfsBuffer
CALL sbfsBufferOut
; "SBFS", or this is not a disk of ours. A blank image is all zeroes, so without this
; an unformatted disk would look like a formatted one with no files on it.
SETD.0 SbfsBuffer
SETD.2 SbfsMagic
INIA 0d4
SETD.1 SbfsCount
STA.1
sbfsMagicLoop:
CALL sbfsSameByte
BRQ sbfsMagicSame
RET ; Q is the difference, which is not zero.
sbfsMagicSame:
INCD.0
INCD.2
LDA.1
DECA
STA.1
BNA sbfsMagicLoop
sbfsMagicDone:
; The version has to be one we understand, and there are two of them.
;
; Version one is flat: every file is in the root because there is nowhere else. Version
; two gives each entry a parent, and writes it as the entry's index PLUS ONE - so the
; zeroes a version one disk has in those bytes read as "in the root", which is exactly
; where all of its files are. A version one disk needs nothing done to it to be read
; here, and that is why both numbers are taken rather than one being converted.
SETD.0 SbfsBuffer
DPUP.0 0d04
LDA.0
INIB 0d1
XOR
BRQ sbfsGeometry
SETD.0 SbfsBuffer
DPUP.0 0d04
LDA.0
INIB 0d2
XOR
BRQ sbfsGeometry
RET ; A version we do not know.
sbfsGeometry:
; Where the directory is and how big it is. The superblock carries both so that disks
; of different sizes can have different directories without a new format.
SETD.0 SbfsBuffer
DPUP.0 0d08
SETD.1 SbfsDirStart
CALL sbfsCopyWord
SETD.0 SbfsBuffer
DPUP.0 0d10
SETD.1 SbfsDirBlocks
CALL sbfsCopyWord
; A DIRECTORY WHOSE LAST ENTRIES CANNOT BE NAMED AS A PARENT. Eight entries to a block,
; and the parent is an index plus one in two bytes, so entry 65535 has no parent number
; at all - adding one wraps to zero, and zero is the root.
;
; It does not fail by refusing. Anything created inside such a directory writes a parent
; of zero and lands in the ROOT, while whatever asked reports the path it wanted;
; looking there afterwards finds nothing, because the search is for a parent the entry
; does not carry, so the same create succeeds over and over and piles up entries of one
; name in the root. Two entries of one name in one place is the thing rename refuses
; outright, and this made them by the handful.
;
; 8191 blocks is the most, so anything from 0x2000 up is refused. Only the high byte has
; to be looked at to know.
SETD.0 SbfsDirBlocks
LDA.0
INIB 0x20
CCF
SUB
BNC sbfsMountTooBig ; The high byte is 0x20 or more, so more than 8191 blocks.
SETD.0 SbfsBuffer
DPUP.0 0d06
SETD.1 SbfsDiskBlocks
CALL sbfsCopyWord
RSTA
RSTB
CCF
ADD ; Q is zero: mounted.
RET
sbfsMountTooBig:
RSTA
INIB 0d1
CCF
ADD ; Q is not zero: not a disk this will mount.
RET
; ---- Finding something by path ----
;
; DP0 points at a path ending in a zero byte: names with '/' between them. A path that
; begins with a separator is walked from the root, and anything else from SbfsCwd, which
; is where the machine currently is.
;
; Q is zero if it was found, and then SbfsFileStart, SbfsFileBlocks and SbfsFileTail
; describe it, SbfsFoundFlags says what kind of thing it is, and DP3 is left on the entry
; with SbfsBlock on the directory block it came out of - which is what deleting and
; renaming need in order to change it and put it back.
;
; A BARE NAME IS A PATH OF ONE NAME, so everything written before there were directories
; still works and still costs one walk of the directory. It now means a name in the
; working directory rather than a name in the root, which is the whole of what a working
; directory is, and no caller had to be told.
;
; Each name is looked for among the entries whose parent is where the walk has got to.
; There is no list of children anywhere: being a child is a fact written in the child, so
; finding them means looking at all of them. That is the same walk the flat version did
; with one more thing compared, which is why a flat disk costs what it always did - and on
; a version one disk every entry says "the root", so the comparison is free and true.
;
; sbfsFind is sbfsWalk with one thing added: the root is not a file. The two are separate
; because moving about wants the other answer - "cd /" and "cd .." both end at the root
; quite legitimately, and would have no way to say so through a routine that calls it a
; failure.
sbfsFind:
CALL sbfsWalk
BNQ sbfsFindNoWalk
; Did the walk get anywhere at all? The root is a place, but it is not a file.
SETD.0 SbfsAt
LDA.0
INCD.0
LDB.0
OR
BRQ sbfsFindRoot
RSTA
RSTB
CCF
ADD ; Q is zero: found.
sbfsFindNoWalk:
RET
sbfsFindRoot:
RSTA
INIB 0d1
CCF
ADD
RET
; The walk itself. Q is zero if the whole path was walked, and SbfsAt says where it ended -
; which may be the root, and that is an answer rather than a failure.
sbfsWalk:
SETD.1 SbfsPathAt
STD.0.1
; Where it starts. A path beginning with a separator is measured from the root, which is
; zero because a parent is an entry index PLUS ONE and the root is not an entry.
; Anything else is measured from wherever the machine already is.
LDA.0
INIB 0x2F
CCF
SUB
BRQ sbfsWalkFromRoot
SETD.0 SbfsCwd
SETD.1 SbfsAt
CALL sbfsCopyWord
; Where the machine is, is a directory - it could not have been got to otherwise - but
; nothing here has read its entry, so what describes it is whatever the last find left
; behind. Say the one thing about it that the walk needs, and mark the rest as not to be
; believed, exactly the way going up does.
INIA 0x02
SETD.0 SbfsFoundFlags
STA.0
RSTA
SETD.0 SbfsFieldsValid
STA.0
BRI sbfsFindName
sbfsWalkFromRoot:
SETD.0 SbfsAt
RSTA
STA.0
INCD.0
STA.0
; Nothing described yet. An empty path comes back as the root, which is right.
RSTA
SETD.0 SbfsFieldsValid
STA.0
sbfsFindName:
CALL sbfsPathNext
SETD.0 SbfsPathState
LDA.0
BRA sbfsFindGotName
INIB 0d1
CCF
SUB
BRQ sbfsFindEnd ; The path ran out.
BRI sbfsFindMissing ; A name longer than a name can be, so nothing is called it.
sbfsFindGotName:
; "." and ".." belong to the filesystem and are answered here rather than looked for.
; Nothing on a disk is ever called either of them, so this takes nothing away.
SETD.0 SbfsWanted
LDA.0
INIB 0x2E
CCF
SUB
BNQ sbfsFindLook
INCD.0
LDA.0
BRA sbfsFindName ; "." on its own is where the walk already is.
INIB 0x2E
CCF
SUB
BNQ sbfsFindLook
INCD.0
LDA.0
BRA sbfsFindUp ; ".." on its own goes back the way it came.
sbfsFindLook:
; Only a directory can be looked inside. Where the walk is now was put there by the last
; scan, so what kind of thing it is has already been read out of its entry.
SETD.0 SbfsAt
LDA.0
INCD.0
LDB.0
OR
BRQ sbfsFindScan ; At the root, which can always be looked inside.
SETD.0 SbfsFoundFlags
LDA.0
INIB 0x02
AND
BRQ sbfsFindMissing ; Not a directory, so there is nothing inside it.
sbfsFindScan:
CALL sbfsScanFor
BNQ sbfsFindMissing
BRI sbfsFindName
sbfsFindUp:
; ".." from the root is the root. Every filesystem answers this way, and it is the only
; answer that cannot walk off the top of the disk.
SETD.0 SbfsAt
LDA.0
INCD.0
LDB.0
OR
BRQ sbfsFindName
; Where the walk is, as an index rather than as a parent.
SETD.0 SbfsAt
SETD.1 SbfsTarget
CALL sbfsCopyWord
SETD.0 SbfsTarget
CALL sbfsBackWord
CALL sbfsAtIndex
BNQ sbfsFindMissing ; The disk would not read.
SETD.0 SbfsUpParent
SETD.1 SbfsAt
CALL sbfsCopyWord
; What it landed on is a directory, because a parent always is. What describes it, on
; the other hand, is the entry it came FROM - so that is marked as not to be believed,
; and loaded properly if the path stops here.
INIA 0x02
SETD.0 SbfsFoundFlags
STA.0
RSTA
SETD.0 SbfsFieldsValid
STA.0
BRI sbfsFindName
sbfsFindEnd:
; Ending at the root is a perfectly good answer here, and there is nothing to describe.
SETD.0 SbfsAt
LDA.0
INCD.0
LDB.0
OR
BRQ sbfsFindGood
SETD.0 SbfsFieldsValid
LDA.0
BNA sbfsFindGood
; The path ended on a "..", so what describes the entry is one place out of date.
SETD.0 SbfsAt
SETD.1 SbfsTarget
CALL sbfsCopyWord
SETD.0 SbfsTarget
CALL sbfsBackWord
CALL sbfsAtIndex
BNQ sbfsFindMissing
sbfsFindGood:
RSTA
RSTB
CCF
ADD ; Q is zero: found.
RET
sbfsFindMissing:
; Nothing of that name. Q has to be something other than zero to say so.
RSTA
INIB 0d1
CCF
ADD
RET
; ---- Splitting a path into where and what ----
;
; DP0 points at a path. Everything but the last name is walked, so what comes back is the
; directory a thing should be MADE in and the name to make it under: SbfsAt is the
; directory and SbfsWanted holds the name, padded to twenty two the way an entry holds one.
; Q is zero if that worked.
;
; The head is copied rather than the path being cut in place. The path belongs to whoever
; called, and a routine that writes a zero byte into somebody else's string is one that has
; to put it back on every way out, including the ways out that failed.
;
; THE SEPARATOR STAYS ON THE END OF THE HEAD, and that is what makes one rule cover both
; kinds of path. "/x" leaves a head of "/", which is the root; "x" leaves an empty head,
; which is where the machine already is; and "A/x" leaves "A/", which is neither of those
; and needs no special case to say so.
sbfsWalkParent:
RSTA
SETD.1 SbfsHeadLen
STA.1
SETD.1 SbfsSpanAt
STA.1
PSHD.0
POPD.2 ; DP2 walks the path, DP0 stays on the front of it.
sbfsSplitScan:
LDA.2
BRA sbfsSplitEnd
INIB 0x2F
CCF
SUB
BNQ sbfsSplitStep
; A separator. The head runs to just past it, so the last one to be seen wins.
SETD.1 SbfsSpanAt
LDA.1
INCA
SETD.1 SbfsHeadLen
STA.1
sbfsSplitStep:
SETD.1 SbfsSpanAt
LDA.1
INCA
STA.1
BRA sbfsSplitTooLong ; Round past two hundred and fifty five: not a path.
INCD.2
BRI sbfsSplitScan
sbfsSplitEnd:
; The head, up to and including the separator that ended it.
PSHD.0
POPD.2
SETD.1 SbfsHead
SETD.0 SbfsHeadLen
LDA.0
INIB 0d95
CCF
SUB
BNC sbfsSplitTooLong ; Longer than there is room to copy it into.
SETD.0 SbfsHeadLen
LDA.0
SETD.0 SbfsSpanAt
STA.0 ; Counting it back down again.
sbfsHeadCopy:
SETD.0 SbfsSpanAt
LDA.0
BRA sbfsHeadDone
DECA
STA.0
LDA.2
STA.1
INCD.2
INCD.1
BRI sbfsHeadCopy
sbfsHeadDone:
RSTA
STA.1 ; The zero that ends the head.
; And the last name, which is whatever DP2 is now on. Measured before it is copied,
; because twenty two is all an entry holds and a longer name is refused rather than cut
; down - a name cut to twenty two characters is a different name and might well be
; taken. Measuring is the only way to know: looking at the twenty third character of a
; shorter name reads past the end of somebody else's string.
PSHD.2
POPD.0
LDA.0
BRA sbfsSplitNoName ; The path ended in a separator, so it names nothing.
RSTA
SETD.1 SbfsSpanAt
STA.1
sbfsLeafMeasure:
LDA.2
BRA sbfsLeafMeasured
SETD.1 SbfsSpanAt
LDA.1
INCA
STA.1
INIB 0d23
CCF
SUB
BRQ sbfsSplitTooLong
INCD.2
BRI sbfsLeafMeasure
sbfsLeafMeasured:
; KEPT SOMEWHERE OF ITS OWN, and this is not tidiness. Walking the head goes through
; sbfsPathNext, which puts every name it meets into SbfsWanted on its way past - so the
; last name of the head would land exactly where the leaf was and the thing would be
; created under the name of the directory it was going into. "mkdir Apps/Deep" made
; /Apps/Apps.
SETD.1 SbfsLeaf
CALL sbfsKeepName
; Now where it goes. The head is walked exactly the way any other path is.
SETD.0 SbfsHead
CALL sbfsWalk
BNQ sbfsSplitNoName
; And the leaf comes back out, now that nothing else is going to write there.
SETD.0 SbfsLeaf
SETD.1 SbfsWanted
INIA 0d22
SETD.2 SbfsCount
STA.2
sbfsLeafBack:
LDA.0
STA.1
INCD.0
INCD.1
LDA.2
DECA
STA.2
BNA sbfsLeafBack
; And it has to be somewhere things can be put. The root always is.
SETD.0 SbfsAt
LDA.0
INCD.0
LDB.0
OR
BRQ sbfsSplitGood
SETD.0 SbfsFoundFlags
LDA.0
INIB 0x02
AND
BRQ sbfsSplitNoName
sbfsSplitGood:
RSTA
RSTB
CCF
ADD
RET
sbfsSplitTooLong:
sbfsSplitNoName:
RSTA
INIB 0d1
CCF
ADD
RET
; ---- Taking a path apart ----
;
; Copies the next name out of the path into SbfsWanted, padded with zeroes to twenty two
; the way an entry holds one, and moves SbfsPathAt past it.
;
; SbfsPathState says what happened: zero for a name, one for the end of the path, two for
; a name longer than a name can be. THE LAST IS REFUSED RATHER THAN CUT SHORT, because a
; name cut to twenty two characters is a different name, and might well be some other
; file's.
;
; Separators are skipped rather than counted, so "/Apps/", "Apps" and "//Apps" all walk
; the same way and a trailing one simply ends the path.
sbfsPathNext:
RSTA
SETD.0 SbfsPathState
STA.0
SETD.0 SbfsPathAt
LDD.1.0
sbfsPathSkip:
LDA.1
BRA sbfsPathEnd
INIB 0x2F
CCF
SUB
BNQ sbfsPathName
INCD.1
BRI sbfsPathSkip
sbfsPathEnd:
INIA 0d1
SETD.0 SbfsPathState
STA.0
BRI sbfsPathSave
sbfsPathName:
SETD.2 SbfsWanted
INIA 0d22
SETD.0 SbfsPathLeft
STA.0
sbfsPathCopy:
LDA.1
BRA sbfsPathPad ; The path ended, so the name ended with it.
INIB 0x2F
CCF
SUB
BRQ sbfsPathPad ; A separator ends the name.
SETD.0 SbfsPathLeft
LDA.0
BRA sbfsPathTooLong ; Twenty two already, and there is still more of it.
DECA
STA.0
LDA.1
STA.2
INCD.1
INCD.2
BRI sbfsPathCopy
sbfsPathPad:
; Zeroes out to the twenty two, so that comparing the whole field compares the name.
SETD.0 SbfsPathLeft
LDA.0
BRA sbfsPathSave
sbfsPathPadLoop:
RSTA
STA.2
INCD.2
SETD.0 SbfsPathLeft
LDA.0
DECA
STA.0
BNA sbfsPathPadLoop
sbfsPathSave:
SETD.0 SbfsPathAt
STD.1.0
RET
sbfsPathTooLong:
INIA 0d2
SETD.0 SbfsPathState
STA.0
RET
; ---- Looking in one directory ----
;
; Looks for the name in SbfsWanted among the entries whose parent is SbfsAt. Q is zero if
; it is there, and then the walk moves onto it and everything that describes it is read
; out of its entry. DP3 is left on that entry.
sbfsScanFor:
SETD.0 SbfsDirStart
SETD.1 SbfsBlock
CALL sbfsCopyWord
SETD.0 SbfsDirBlocks
INCD.0
LDA.0
SETD.1 SbfsLeft
STA.1 ; Only the low byte: a directory of 256 blocks is 2048 entries.
; Entries are COUNTED rather than worked out from where they sit. An index becomes a
; block and an offset by dividing by eight, and this machine has no divide; counting
; costs one step per entry through a walk that was happening anyway.
SETD.0 SbfsScanIndex
RSTA
STA.0
INCD.0
STA.0
sbfsScanBlock:
CALL sbfsReadBlock
BRQ sbfsScanLoaded
RET ; The read failed.
sbfsScanLoaded:
SETD.1 SbfsBuffer
CALL sbfsBufferOut
; Eight entries to a block, thirty two bytes each.
SETD.2 SbfsBuffer
INIA 0d8
SETD.1 SbfsCount
STA.1
sbfsScanEntry:
LDA.2
INIB 0x01
AND
BRQ sbfsScanNext ; The in use bit is down, so this entry is free.
CALL sbfsMatchParent
BNQ sbfsScanNext ; It lives somewhere else.
CALL sbfsMatchEntry
BRQ sbfsScanFound
sbfsScanNext:
SETD.0 SbfsScanIndex
CALL sbfsStepWord
DPUP.2 0d32
LDA.1
DECA
STA.1
BNA sbfsScanEntry
sbfsScanNextBlock:
SETD.0 SbfsBlock
CALL sbfsStepWord
SETD.1 SbfsLeft
LDA.1
DECA
STA.1
BRA sbfsScanMissing
BRI sbfsScanBlock
sbfsScanMissing:
RSTA
INIB 0d1
CCF
ADD
RET
sbfsScanFound:
; DP2 is on the entry. Keep it in DP3 while the pieces are taken out of it: DP3 is the
; pointer a CALL does not put back, so it is the only one that survives a subroutine.
PSHD.2
POPD.3
CALL sbfsTakeEntry
; The walk moves onto what it found, written the way a parent is written.
SETD.0 SbfsScanIndex
SETD.1 SbfsAt
CALL sbfsCopyWord
SETD.0 SbfsAt
CALL sbfsStepWord
RSTA
RSTB
CCF
ADD ; Q is zero: found.
RET
; DP2 is on an entry. Q is zero if it lives in the directory SbfsHoldAt names. The third
; of these, and the reason all three are subroutines: a RET puts DP2 back on the entry.
sbfsMatchHold:
PSHD.2
POPD.0
DPUP.0 0d28
SETD.2 SbfsHoldAt
CALL sbfsSameByte
BNQ sbfsMatchHoldDone
INCD.0
INCD.2
CALL sbfsSameByte
sbfsMatchHoldDone:
RET
; DP2 is on an entry. Q is zero if it lives in the directory the machine is in. The same
; comparison sbfsMatchParent makes, against the other of the two places a walk can be.
sbfsWalkHere:
PSHD.2
POPD.0
DPUP.0 0d28
SETD.2 SbfsCwd
CALL sbfsSameByte
BNQ sbfsWalkHereDone
INCD.0
INCD.2
CALL sbfsSameByte
sbfsWalkHereDone:
RET
; DP2 is on an entry. Q is zero if it lives in the directory the walk is looking in.
;
; On a version one disk these two bytes are zero in every entry, and the walk starts at
; zero, so this always agrees - which is exactly how a flat disk reads correctly here
; without anything having been done to it.
sbfsMatchParent:
PSHD.2
POPD.0
DPUP.0 0d28
SETD.2 SbfsAt
CALL sbfsSameByte
BNQ sbfsMatchParentDone
INCD.0
INCD.2
CALL sbfsSameByte
sbfsMatchParentDone:
RET
; ---- Going back up ----
;
; Walks the directory to the entry SbfsTarget names and takes it apart, SbfsUpParent
; included. Q is zero if it got there.
;
; WALKING TO AN INDEX RATHER THAN WORKING OUT WHERE IT SITS. An index becomes a block and
; an offset by dividing by eight, and this machine has no divide. The walk costs a few
; block reads and no arithmetic at all, and only ".." ever needs it.
sbfsAtIndex:
SETD.0 SbfsDirStart
SETD.1 SbfsBlock
CALL sbfsCopyWord
SETD.0 SbfsDirBlocks
INCD.0
LDA.0
SETD.1 SbfsLeft
STA.1
SETD.0 SbfsScanIndex
RSTA
STA.0
INCD.0
STA.0
sbfsAtBlock:
CALL sbfsReadBlock
BRQ sbfsAtLoaded
RET ; The read failed.
sbfsAtLoaded:
SETD.1 SbfsBuffer
CALL sbfsBufferOut
SETD.2 SbfsBuffer
INIA 0d8
SETD.1 SbfsCount
STA.1
sbfsAtEntry:
; Where the entry is has to be put down for the length of the comparison, because
; comparing two numbers wants DP2 for one of them.
PSHD.2
SETD.0 SbfsScanIndex
SETD.2 SbfsTarget
CALL sbfsCompareWord
POPD.2
BRQ sbfsAtFound
SETD.0 SbfsScanIndex
CALL sbfsStepWord
DPUP.2 0d32
LDA.1
DECA
STA.1
BNA sbfsAtEntry
SETD.0 SbfsBlock
CALL sbfsStepWord
SETD.1 SbfsLeft
LDA.1
DECA
STA.1
BRA sbfsAtMissing
BRI sbfsAtBlock
sbfsAtMissing:
RSTA
INIB 0d1
CCF
ADD
RET
sbfsAtFound:
PSHD.2
POPD.3
CALL sbfsTakeEntry
; And the name, which only this way of arriving at an entry needs: walking up a chain of
; parents to write out where the machine is wants the name at every step. Copied here
; rather than in sbfsTakeEntry, because every find in the system goes through that one
; and none of them wants twenty two bytes moved on its behalf.
PSHD.3
POPD.0
DPUP.0 0d06
SETD.1 SbfsName
INIA 0d22
SETD.2 SbfsCount
STA.2
sbfsAtName:
LDA.0
STA.1
INCD.0
INCD.1
LDA.2
DECA
STA.2
BNA sbfsAtName
RSTA
STA.1 ; The twenty third byte, which makes it a string.
RSTA
RSTB
CCF
ADD
RET
; DP3 is on an entry. Takes it apart into everything that describes what was found.
;
; Written once and called from both the scan and the walk to an index, because two copies
; of "which byte means what" is the kind of thing that stays right until one of them is
; changed.
sbfsTakeEntry:
LDA.3
SETD.0 SbfsFoundFlags
STA.0
PSHD.3
POPD.0
INCD.0
SETD.1 SbfsFileStart
CALL sbfsCopyWord
PSHD.3
POPD.0
DPUP.0 0d03
SETD.1 SbfsFileBlocks
CALL sbfsCopyWord
PSHD.3
POPD.0
DPUP.0 0d05
LDA.0
SETD.1 SbfsFileTail
STA.1
PSHD.3
POPD.0
DPUP.0 0d28
SETD.1 SbfsUpParent
CALL sbfsCopyWord
INIA 0x01
SETD.0 SbfsFieldsValid
STA.0
RET
; Takes one from the two byte number at DP0, the other way round from sbfsStepWord.
sbfsBackWord:
INCD.0
LDA.0
DECA
STA.0
BNC sbfsBackDone ; It did not borrow, so the high byte is untouched.
DECD.0
LDA.0
DECA
STA.0
sbfsBackDone:
RET
; ---- Walking the directory ----
;
; sbfsFind answers a question about one name. Listing what is on a disk is a different
; job: it needs the directory walked rather than searched. sbfsFirst starts a walk and
; sbfsNext steps it, and each of them stops on an entry that is in use, skipping the free
; ones on the way past.
;
; Q is zero while there is an entry to look at. When it is, SbfsName holds the name with
; a zero byte after it, and SbfsFileStart, SbfsFileBlocks and SbfsFileTail describe the
; file exactly the way sbfsFind leaves them. Q is something else when the directory is
; finished, and also when a block could not be read, which are the same answer to the
; question "is there another one" and different answers to "why not".
;
; A walk keeps a directory block in SbfsBuffer between calls, so anything else that goes
; to the disk in the middle of one ends it. Take what is wanted out of an entry before
; asking the disk for anything else.
sbfsFirst:
SETD.0 SbfsDirStart
SETD.1 SbfsWalkBlock
CALL sbfsCopyWord
SETD.0 SbfsDirBlocks
INCD.0
LDA.0
SETD.1 SbfsWalkLeft
STA.1 ; Only the low byte, the same as sbfsFind.
; Nothing is loaded yet. Saying the block in hand is empty makes the scan fetch the
; first one, so there is one way into a block rather than two.
RSTA
SETD.0 SbfsWalkCount
STA.0
BRI sbfsWalkScan
sbfsNext:
; The pointer and the count were stepped when the last entry was handed out, so there
; is nothing to do here but carry on looking.
BRI sbfsWalkScan
sbfsWalkScan:
; Anything left in the block in hand?
SETD.0 SbfsWalkCount
LDA.0
BNA sbfsWalkEntry
; No. Take the next directory block, if the directory has one.
SETD.0 SbfsWalkLeft
LDA.0
BRA sbfsWalkEnd
DECA
STA.0
SETD.0 SbfsWalkBlock
SETD.1 SbfsBlock
CALL sbfsCopyWord
CALL sbfsReadBlock
BRQ sbfsWalkLoaded
RET ; The read failed, and Q says so.
sbfsWalkLoaded:
SETD.1 SbfsBuffer
CALL sbfsBufferOut
; That one is in hand now, so the walk's block number moves on to the following one.
SETD.0 SbfsWalkBlock
CALL sbfsStepWord
; Eight entries to a block, starting at the top of the buffer.
SETD.0 SbfsBuffer
SETD.1 SbfsWalkPointer
STD.0.1
INIA 0d8
SETD.0 SbfsWalkCount
STA.0
BRI sbfsWalkScan
sbfsWalkEntry:
; Where this entry is. Kept in memory rather than in DP3, so that a walk does not
; quietly take the one pointer a caller can carry things across a call in.
SETD.1 SbfsWalkPointer
LDD.2.1
SETD.1 SbfsWalkAt
STD.2.1
; Step past it now, so that the walk has moved on whether this one is taken or skipped.
; Getting that wrong in only one of the two paths is how a walk repeats an entry
; forever, and it repeats the interesting ones rather than the boring ones.
SETD.0 SbfsWalkCount
LDA.0
DECA
STA.0
PSHD.2
POPD.0
DPUP.0 0d32
SETD.1 SbfsWalkPointer
STD.0.1
; Is it a file? A free entry is not one, and there can be free entries in the middle of
; a directory, so this is a skip rather than a stop.
LDA.2
INIB 0x01
AND
BRQ sbfsWalkScan
; And is it in the directory the machine is in? The entries of every directory on the
; disk are mixed together in one array - being a child is a fact written in the child,
; not a list kept anywhere - so a walk that wants one directory has to say which, and
; everything else is stepped over on the way past.
CALL sbfsWalkHere
BNQ sbfsWalkScan
CALL sbfsWalkTake
RSTA
RSTB
CCF
ADD ; Q is zero: here is an entry.
RET
sbfsWalkEnd:
RSTA
INIB 0d1
CCF
ADD ; Q is one: the directory is finished.
RET
; Takes the pieces out of the entry the walk stopped on. Everything lands in memory,
; because that is the only place a subroutine can leave anything.
sbfsWalkTake:
; What kind of thing it is, so that a listing can say so. A directory has no blocks, and
; without this it would be handed out as a file of no bytes - which is a different thing
; that happens to look the same from here.
SETD.1 SbfsWalkAt
LDD.0.1
LDA.0
SETD.1 SbfsFoundFlags
STA.1
SETD.1 SbfsWalkAt
LDD.0.1
INCD.0
SETD.1 SbfsFileStart
CALL sbfsCopyWord
SETD.1 SbfsWalkAt
LDD.0.1
DPUP.0 0d03
SETD.1 SbfsFileBlocks
CALL sbfsCopyWord
SETD.1 SbfsWalkAt
LDD.0.1
DPUP.0 0d05
LDA.0
SETD.1 SbfsFileTail
STA.1
; The name. Twenty two bytes of it, padded with zeroes rather than terminated, so it is
; copied into a buffer with a twenty third byte that nothing ever writes. That byte is
; what makes a name that fills the field into a string that can be printed.
SETD.1 SbfsWalkAt
LDD.0.1
DPUP.0 0d06
SETD.1 SbfsName
INIA 0d22
SETD.2 SbfsCount
STA.2
sbfsWalkName:
LDA.0
STA.1
INCD.0
INCD.1
SETD.2 SbfsCount
LDA.2
DECA
STA.2
BNA sbfsWalkName
RET
; Compares the name in the entry at DP2 with the one kept in SbfsWanted. Q is zero if
; they are the same. Names are padded with zeroes rather than terminated, so a name that
; fills the field has no terminator to look for, which is why the count is what stops it.
; A COUNTER OF ITS OWN, and that matters more than it looks. sbfsFind counts the eight
; entries of a block in SbfsCount and calls this for each one; when this used SbfsCount too,
; a failed comparison left the ENTRY count holding however far the NAME comparison had got.
; A name differing at its first byte left 22 there, so the search walked twenty two entries
; through a buffer holding eight - off the end of it, into whatever data happened to follow,
; and reported a match against rubbish. What followed the buffer decided whether it looked
; like it worked, which is why it went unnoticed until unrelated data was added.
sbfsMatchEntry:
PSHD.2
POPD.0
DPUP.0 0d06 ; The name inside the entry.
SETD.2 SbfsWanted
INIA 0d22
SETD.1 SbfsMatchLeft
STA.1
sbfsMatchLoop:
CALL sbfsSameByte
BRQ sbfsMatchSame
RET ; They differ, and Q is the difference.
sbfsMatchSame:
LDA.0
BRA sbfsMatchYes ; Both ended in the same place.
INCD.0
INCD.2
LDA.1
DECA
STA.1
BNA sbfsMatchLoop ; Twenty two the same is the same name, so falling out is a match.
sbfsMatchYes:
RSTA
RSTB
CCF
ADD
RET
; Twenty two bytes from DP0 to DP1, which is one name exactly as an entry holds it. Not
; sbfsCopyWord's job and not sbfsKeepName's either: this one is for a name that is already
; padded and is only being put somewhere safe.
sbfsCopyName:
INIA 0d22
SETD.2 SbfsCount
STA.2
sbfsCopyNameLoop:
LDA.0
STA.1
INCD.0
INCD.1
LDA.2
DECA
STA.2
BNA sbfsCopyNameLoop
RET
; Copies the name at DP0 into DP1, twenty two bytes of it, padding with zeroes the way an
; entry is padded so that the two can be compared as they stand.
sbfsKeepName:
INIA 0d22
SETD.2 SbfsCount
STA.2
RSTB ; B stays zero once the name has ended.
sbfsKeepLoop:
LDA.0
BRA sbfsKeepPad
STA.1
INCD.0
BRI sbfsKeepStep
sbfsKeepPad:
STB.1
sbfsKeepStep:
INCD.1
LDA.2
DECA
STA.2
BNA sbfsKeepLoop
sbfsKeepDone:
RET
; Reads the file that sbfsFind found into Data Memory at DP1. Q is zero if it worked.
;
; Whole blocks are copied whole, including the last one, so the bytes after the end of a
; file are whatever else was in that block on the disk. SbfsFileTail says where the file
; actually stops, and it is the caller's business to respect it.
;
; A file of more than 255 blocks is not handled here. That is 64K, which is the whole of
; Data Memory, so it could not be read into it anyway.
sbfsRead:
PSHD.1
POPD.3 ; Where it goes. DP3 survives a CALL, and nothing called here
; touches it.
SETD.0 SbfsFileStart
SETD.1 SbfsBlock
CALL sbfsCopyWord
SETD.0 SbfsFileBlocks
INCD.0
LDA.0
SETD.1 SbfsLeft
STA.1
SETD.0 SbfsFileTail
LDA.0
BRA sbfsReadCounted ; No part block on the end.
SETD.0 SbfsLeft
LDA.0
INCA
STA.0 ; One more block for the tail.
sbfsReadCounted:
SETD.0 SbfsLeft
LDA.0
BRA sbfsReadDone ; An empty file has nothing to read.
sbfsReadLoop:
CALL sbfsReadBlock
BRQ sbfsReadGot
RET ; The read failed, and Q says so.
sbfsReadGot:
PSHD.3
POPD.1
CALL sbfsBufferOut
; On by a whole block. DPUP carries one byte at a time, so 256 takes two of them.
DPUP.3 0xFF
INCD.3
SETD.0 SbfsBlock
CALL sbfsStepWord
SETD.0 SbfsLeft
LDA.0
DECA
STA.0
BNA sbfsReadLoop
sbfsReadDone:
RSTA
RSTB
CCF
ADD ; Q is zero: read.
RET
; Reads one block of the file sbfsFind found, the one SbfsIndex names counting from zero,
; into Data Memory at DP1. Q is zero if it worked.
;
; This is the whole of streaming: a file too big to hold is read a block at a time by
; asking for each in turn, and nothing has to be kept between the calls but the number.
; sbfsRead is what this would be if it were called in a loop, which is why the two look
; alike; it stays as it is because reading a whole small file is what most callers want
; and doing it in one call is both shorter and faster.
;
; The whole block comes across, including a last one that the file only partly fills, so
; the bytes past the end of it are whatever else was on the disk there. SbfsFileTail says
; where the file stops and it is the caller's business to respect it, the same bargain
; sbfsRead offers.
;
; An index past the end of the file is not caught here. It reads whatever block that
; works out to, which is somebody else's file or free space; the caller knows how many
; blocks there are, because sbfsFileExtent tells it.
sbfsReadOne:
PSHD.1
POPD.3 ; Where it goes. DP3 is the one pointer a CALL does not put back.
SETD.0 SbfsBlock
SETD.2 SbfsFileStart
CALL sbfsSetWord
SETD.0 SbfsBlock
SETD.2 SbfsIndex
CALL sbfsAddWord
; ---- READ AHEAD ----
;
; Is this block already coming? It will be if the last time through asked for the one
; before it, which is what reading a file front to back does every time. Then there is
; nothing to start: the disk has been fetching it while the caller was busy with the last
; one, and all that is left is to wait for it.
;
; This is the path a search is NOT. A directory scan stops the moment it matches, so
; asking for the next block there is asking for one nobody will look at - and it was
; nineteen per cent slower for exactly that reason. A file is read to its end, so every
; block asked for early is one that would have been asked for anyway.
SETD.0 SbfsBufferKnown
LDA.0
BRA sbfsReadOneFresh
SETD.0 SbfsBufferBlock
SETD.2 SbfsBlock
CALL sbfsCompareWord
BNQ sbfsReadOneFresh
RCAL sbfsWaitDisk ; Already on its way, so only the waiting is left.
INIB 0x02
AND
BNQ sbfsReadOneDone
BRI sbfsReadOneHere
sbfsReadOneFresh:
CALL sbfsReadBlock
BNQ sbfsReadOneDone ; The read failed, and Q says so.
sbfsReadOneHere:
PSHD.3
POPD.1
CALL sbfsBufferOut
; And the one after it, started now, if the file has one. Bounded by the file's own
; length so that reading the last block does not fetch whatever follows the file on the
; disk - which belongs to somebody else and would be paid for twice: once to fetch and
; once to throw away.
; IN A PLACE OF ITS OWN, not in SbfsIndex. What block was asked for is the caller's, and
; it is still wanted after this returns - handleFileBlock compares it against the file's
; length to work out whether this was the short last block. Stepping it here made every
; block report the wrong number of bytes.
CALL sbfsFileExtent
SETD.0 SbfsAheadIndex
SETD.2 SbfsIndex
CALL sbfsSetWord
SETD.0 SbfsAheadIndex
CALL sbfsStepWord
SETD.0 SbfsAheadIndex
SETD.2 SbfsWantBlocks
CALL sbfsCompareWord
BNC sbfsReadOneLast ; The next one is past the end of the file.
SETD.0 SbfsBlock
CALL sbfsStepWord
RCAL sbfsStartRead
sbfsReadOneLast:
RSTA
RSTB
CCF
ADD ; Q is zero: read.
sbfsReadOneDone:
RET
; ---- Writing one block of a file ----
;
; The other half of sbfsReadOne, and deliberately the same shape. DP1 is where the block
; comes FROM and SbfsIndex says which block of the file it is, counting from zero. The file
; is whichever one the last find landed on, exactly as it is for reading.
;
; THE INDEX IS CHECKED AGAINST THE FILE'S LENGTH, and that check is not politeness. Files
; are laid down contiguously, so block N of a five block file is a real block belonging to
; whatever happens to sit five blocks along - and writing it would put one file's bytes
; inside another with nothing anywhere saying so. Reading past the end is a wrong answer;
; writing past it is somebody else's file.
sbfsWriteOne:
PSHD.1
POPD.3 ; Where it comes from. DP3 survives the calls below.
CALL sbfsFileExtent ; How many blocks the file really occupies.
SETD.0 SbfsIndex
SETD.2 SbfsWantBlocks
CALL sbfsCompareWord
BNC sbfsWriteOneNo ; The index is not below the count, so it is past the end.
SETD.0 SbfsBlock
SETD.2 SbfsFileStart
CALL sbfsSetWord
SETD.0 SbfsBlock
SETD.2 SbfsIndex
CALL sbfsAddWord
PSHD.3
POPD.1
CALL sbfsBufferIn
CALL sbfsWriteBlock
RET ; Q is whatever the write said.
sbfsWriteOneNo:
RSTA
INIB 0d1
CCF
ADD
RET
; ---- Writing ----
; Where the first block that can hold a file is: past the superblock and the directory.
sbfsFirstData:
SETD.0 SbfsCandidate
SETD.2 SbfsDirStart
CALL sbfsSetWord
SETD.0 SbfsCandidate
SETD.2 SbfsDirBlocks
CALL sbfsAddWord
RET
; SbfsEntryStart and SbfsEntryEnd describe the file in the entry at DP2. The end is one
; past the last block it holds, and a file of nothing holds none, so its end is its start.
sbfsEntryBounds:
PSHD.2
POPD.3
PSHD.3
POPD.0
INCD.0
SETD.1 SbfsEntryStart
CALL sbfsCopyWord
SETD.0 SbfsEntryEnd
SETD.2 SbfsEntryStart
CALL sbfsSetWord
PSHD.3
POPD.0
DPUP.0 0d03
SETD.1 SbfsScratch
CALL sbfsCopyWord
SETD.0 SbfsEntryEnd
SETD.2 SbfsScratch
CALL sbfsAddWord
PSHD.3
POPD.0
DPUP.0 0d05
LDA.0
BRA sbfsBoundsDone ; No part block on the end.
SETD.0 SbfsEntryEnd
SETD.2 SbfsOne
CALL sbfsAddWord
sbfsBoundsDone:
RET
; Finds a run of SbfsWantBlocks free blocks and puts where it begins in SbfsFileStart.
; Q is zero if there was room.
;
; First fit, walking the directory, because with files laid down contiguously the
; directory already says which blocks are spoken for. There is no allocation table to
; consult and none to keep right.
sbfsAllocate:
CALL sbfsFirstData
sbfsAllocTry:
SETD.0 SbfsCandEnd
SETD.2 SbfsCandidate
CALL sbfsSetWord
SETD.0 SbfsCandEnd
SETD.2 SbfsWantBlocks
CALL sbfsAddWord
; Past the end of the disk means there is nowhere left to look.
SETD.0 SbfsDiskBlocks
SETD.2 SbfsCandEnd
CALL sbfsCompareWord
BRC sbfsAllocNoRoom ; The disk is smaller than where this run would end.
SETD.0 SbfsDirStart
SETD.1 SbfsBlock
CALL sbfsCopyWord
SETD.0 SbfsDirBlocks
INCD.0
LDA.0
SETD.1 SbfsLeft
STA.1
sbfsAllocBlock:
CALL sbfsReadBlock
BNQ sbfsAllocFailed
SETD.1 SbfsBuffer
CALL sbfsBufferOut
SETD.2 SbfsBuffer
INIA 0d8
SETD.1 SbfsCount
STA.1
sbfsAllocEntry:
LDA.2
INIB 0x01
AND
BRQ sbfsAllocNext ; A free entry holds nothing, so it is in nobody's way.
; NOR DOES A DIRECTORY, and this says so rather than leaving it to be true by accident.
;
; It would be true by accident. A directory has no blocks AND no start, so the bounds
; below come out as nought to nought, and the first half of the overlap test - does the
; candidate begin before this entry ends - is false for every candidate there is, since
; they all begin past the directory. Taking these four instructions out changes nothing
; that any test can see, and that was checked rather than assumed.
;
; They stay because what keeps them right is a value written somewhere else. The day
; something gives a directory entry a start - a note about where its children begin, a
; use for a field that is spare today - the overlap test starts answering yes to runs
; that straddle it, and blocks stop being usable for no reason anybody could see from
; here. Four instructions to say "a directory is in nobody's way" where it is meant is
; cheaper than finding that out.
LDA.2
INIB 0x02
AND
BNQ sbfsAllocNext
CALL sbfsEntryBounds
; The comparisons need DP2 for their own purposes, so where this entry is goes on the
; Stack for the duration. Working it out again afterwards was the first way this was
; written, and it was both longer and wrong.
PSHD.2
; Two runs overlap when each begins before the other ends.
SETD.0 SbfsCandidate
SETD.2 SbfsEntryEnd
CALL sbfsCompareWord
BNC sbfsAllocClear
SETD.0 SbfsEntryStart
SETD.2 SbfsCandEnd
CALL sbfsCompareWord
BNC sbfsAllocClear
; They do overlap, so try again from the far end of whatever is in the way.
POPD.2
SETD.0 SbfsCandidate
SETD.2 SbfsEntryEnd
CALL sbfsSetWord
BRI sbfsAllocTry
sbfsAllocClear:
POPD.2
sbfsAllocNext:
DPUP.2 0d32
SETD.1 SbfsCount
LDA.1
DECA
STA.1
BNA sbfsAllocEntry
SETD.0 SbfsBlock
CALL sbfsStepWord
SETD.1 SbfsLeft
LDA.1
DECA
STA.1
BNA sbfsAllocBlock
; Nothing was in the way, so this is where it goes.
SETD.0 SbfsFileStart
SETD.2 SbfsCandidate
CALL sbfsSetWord
RSTA
RSTB
CCF
ADD
RET
sbfsAllocNoRoom:
sbfsAllocFailed:
RSTA
INIB 0d1
CCF
ADD
RET
; The two byte number at DP0 becomes the one at DP2. Written destination first, so that a
; call reads the way an assignment does. sbfsCopyWord goes the other way, source first,
; which is a difference worth keeping in mind: getting it backwards here quietly destroyed
; a value that had just been worked out.
sbfsSetWord:
LDA.2
STA.0
INCD.2
INCD.0
LDA.2
STA.0
RET
; The two byte number at DP0 becomes itself less the one at DP2.
sbfsSubWord:
INCD.0
INCD.2
LDA.0
LDB.2
CCF
SUB
MVQA
STA.0
DECD.0
DECD.2
LDA.0
LDB.2
SUB ; Borrows in from the low half.
MVQA
STA.0
RET
; How many blocks a file of SbfsFileBlocks and SbfsFileTail actually occupies, into
; SbfsWantBlocks. A file of nothing occupies none.
sbfsFileExtent:
SETD.0 SbfsWantBlocks
SETD.2 SbfsFileBlocks
CALL sbfsSetWord
SETD.0 SbfsFileTail
LDA.0
BRA sbfsExtentDone
SETD.0 SbfsWantBlocks
SETD.2 SbfsOne
CALL sbfsAddWord
sbfsExtentDone:
RET
; Makes a file. DP0 names it, and SbfsFileBlocks with SbfsFileTail say how big it is,
; which has to be settled before it is made because nothing here can grow one afterwards.
; Q is zero if it was made, and then SbfsFileStart says where its blocks are.
sbfsCreate:
; Where it goes and what it is called come out of the path together. Everything below
; works from SbfsAt and SbfsWanted, so anything that already knows those two can start
; at sbfsCreateAt and skip the walking.
CALL sbfsWalkParent
BNQ sbfsCreateFailed
sbfsCreateAt:
; A plain file, unless somebody came in at the other door. Set here rather than left
; over from last time, so that one temporary does not make the next ordinary file one.
INIA 0x01
SETD.0 SbfsMakeFlags
STA.0
BRI sbfsCreateGo
; The same, for the half written file a save puts down before it dares touch the original.
; It is an ordinary entry in every other way - it holds blocks and answers to a name - and
; the flag is the whole of what says it is not finished. See sbfsSaveFile.
sbfsCreateTempAt:
INIA 0x05
SETD.0 SbfsMakeFlags
STA.0
sbfsCreateGo:
CALL sbfsFileExtent
CALL sbfsAllocate
BNQ sbfsCreateFailed
; Walk the directory for an entry nobody is using.
SETD.0 SbfsDirStart
SETD.1 SbfsBlock
CALL sbfsCopyWord
SETD.0 SbfsDirBlocks
INCD.0
LDA.0
SETD.1 SbfsLeft
STA.1
sbfsCreateBlock:
CALL sbfsReadBlock
BNQ sbfsCreateFailed
SETD.1 SbfsBuffer
CALL sbfsBufferOut
SETD.2 SbfsBuffer
INIA 0d8
SETD.1 SbfsCount
STA.1
sbfsCreateEntry:
LDA.2
INIB 0x01
AND
BRQ sbfsCreateFill ; This one is free.
DPUP.2 0d32
SETD.1 SbfsCount
LDA.1
DECA
STA.1
BNA sbfsCreateEntry
SETD.0 SbfsBlock
CALL sbfsStepWord
SETD.1 SbfsLeft
LDA.1
DECA
STA.1
BNA sbfsCreateBlock
sbfsCreateFull:
RSTA
INIB 0d1
CCF
ADD ; Every entry is taken.
RET
sbfsCreateFill:
; DP2 is on the entry. Fill it in, then put the whole block back on the disk.
PSHD.2
POPD.3
SETD.0 SbfsMakeFlags
LDA.0
STA.3 ; In use, and possibly not finished being written.
PSHD.3
POPD.1
INCD.1
SETD.0 SbfsFileStart
CALL sbfsCopyWord
PSHD.3
POPD.1
DPUP.1 0d03
SETD.0 SbfsFileBlocks
CALL sbfsCopyWord
PSHD.3
POPD.1
DPUP.1 0d05
SETD.0 SbfsFileTail
LDA.0
STA.1
; WHICH DIRECTORY IT IS IN, written rather than left to be zero by luck. A free entry
; has been wiped by delete or has never been used, so those two bytes would say the root
; on their own - but that is a fact about two other routines, and a fact kept somewhere
; else is one that can be changed without this noticing. A file turning up inside a
; directory it was never put in is not a failure anybody would think to look for.
PSHD.3
POPD.1
DPUP.1 0d28
SETD.0 SbfsAt
CALL sbfsCopyWord
PSHD.3
POPD.1
DPUP.1 0d06
SETD.0 SbfsWanted
INIA 0d22
SETD.2 SbfsCount
STA.2
sbfsCreateName:
LDA.0
STA.1
INCD.0
INCD.1
LDA.2
DECA
STA.2
BNA sbfsCreateName
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
BNQ sbfsCreateFailed
; The free count is a note rather than the truth, but it should still be kept right.
RSTA
SETD.0 SbfsBlock
STA.0
INCD.0
STA.0
CALL sbfsReadBlock
BNQ sbfsCreateFailed
SETD.1 SbfsBuffer
CALL sbfsBufferOut
SETD.0 SbfsBuffer
DPUP.0 0d12
SETD.2 SbfsWantBlocks
CALL sbfsSubWord
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
RET
sbfsCreateFailed:
RSTA
INIB 0d1
CCF
ADD
RET
; Writes a file that sbfsCreate made, from Data Memory at DP1. Q is zero if it worked.
;
; Whole blocks go out whole, so whatever follows the file in Data Memory ends up in the
; unused tail of its last block. That is harmless, since the tail in the entry says where
; the file stops, but it does mean a block can hold a little of whatever was next to it.
sbfsWriteFile:
PSHD.1
POPD.3
SETD.0 SbfsBlock
SETD.2 SbfsFileStart
CALL sbfsSetWord
CALL sbfsFileExtent
SETD.0 SbfsWantBlocks
INCD.0
LDA.0
SETD.1 SbfsLeft
STA.1
BRA sbfsWriteDone ; A file of nothing has nothing to write.
sbfsWriteLoop:
PSHD.3
POPD.1
CALL sbfsBufferIn
CALL sbfsWriteBlock
BNQ sbfsWriteFailed
DPUP.3 0xFF
INCD.3
SETD.0 SbfsBlock
CALL sbfsStepWord
SETD.0 SbfsLeft
LDA.0
DECA
STA.0
BNA sbfsWriteLoop
sbfsWriteDone:
RSTA
RSTB
CCF
ADD
RET
sbfsWriteFailed:
RSTA
INIB 0d1
CCF
ADD
RET
; Copies a whole block from Data Memory at DP1 into the disk's buffer, which is the other
; way round from sbfsBufferOut.
sbfsBufferIn:
INIA 0d1
OUTA 0xE0
PSHD.1
POPA
POPB
OUTB 0xE1
OUTA 0xE2
INIA 0d3
OUTA 0xE3
RSTA
OUTA 0xE4
OUTA 0xE5
INIA 0x01
OUTA 0xE6
RSTA
OUTA 0xE7
INIA 0x01
OUTA 0xE8
RET
; Puts the disk's buffer down as the block named by SbfsBlock. Q is zero if it worked.
sbfsWriteBlock:
RCAL sbfsWaitDisk ; Anything still going finishes before this asks for more.
RCAL sbfsForgetBuffer
SETD.0 SbfsBlock
LDA.0
OUTA 0x20
INCD.0
LDA.0
OUTA 0x21
INIA 0x02
OUTA 0x22
RCAL sbfsWaitDisk
INIB 0x02
AND
RET
; Reads the block named by SbfsBlock into the disk's buffer. Q is zero if it worked.
sbfsReadBlock:
RCAL sbfsStartRead
RCAL sbfsWaitDisk
INIB 0x02
AND ; Q is the error bit, so zero means it worked.
RET
; ---- Asking for a block without waiting for it ----
;
; The half of a read that costs nothing, and the whole of what makes reading ahead
; possible. Whatever the disk was still doing is collected first, because a controller
; given a command while it is busy has no good answer - so this is the one place that
; guarantees it is not, and every read goes through it.
;
; WHICH BLOCK IS COMING IS WRITTEN DOWN, because the disk has one buffer and the only way
; to know what is in it is to remember what was last asked for. Anything that fills the
; buffer some other way must say so by clearing it, or a later read would blit whatever
; happened to be there and call it the block it wanted.
sbfsStartRead:
RCAL sbfsWaitDisk
SETD.0 SbfsBlock
SETD.1 SbfsBufferBlock
CALL sbfsCopyWord
INIA 0x01
SETD.0 SbfsBufferKnown
STA.0
SETD.0 SbfsBlock
LDA.0
OUTA 0x20
INCD.0
LDA.0
OUTA 0x21
INIA 0x01
OUTA 0x22
RRET
; The buffer is about to hold something this cannot describe.
sbfsForgetBuffer:
RSTA
SETD.0 SbfsBufferKnown
STA.0
RRET
; ---- Waiting for the disk ----
;
; The status port has a bit that means the operation is still going, and until now nothing
; here looked at it: the answer was always there before the next instruction was, so asking
; would have been asking about something that could not happen. A disk that takes any time
; at all makes it real, and a program that does not wait reads the block BEFORE the one it
; asked for - which is not an error anywhere, just quietly the wrong bytes.
;
; A REACHES THE CALLER, which is why this is RCAL and not CALL. What comes back is the
; settled status, and CALL would put A back the way it found it - so the one thing this
; exists to hand over is the one thing an ordinary call cannot carry. Two bytes of Stack
; instead of ten, as well, in a routine that runs on every block the machine ever touches.
sbfsWaitDisk:
INA 0x23
INIB 0x01
AND
BNQ sbfsWaitDisk ; The busy bit is up, so round again.
RRET ; A is the status, with the busy bit down.
; Copies the disk's buffer, a whole block of it, to Data Memory at DP1.
sbfsBufferOut:
INIA 0d3
OUTA 0xE0
RSTA
OUTA 0xE1
OUTA 0xE2
INIA 0d1
OUTA 0xE3
PSHD.1
POPA
POPB
OUTB 0xE4
OUTA 0xE5
INIA 0x01
OUTA 0xE6
RSTA
OUTA 0xE7 ; A whole block.
INIA 0x01
OUTA 0xE8
RET
; Two bytes from DP0 to DP1, most significant first, the way every number on a SplitBit
; disk is stored.
sbfsCopyWord:
LDA.0
STA.1
INCD.0
INCD.1
LDA.0
STA.1
RET
; Adds one to the two byte number at DP0.
sbfsStepWord:
INCD.0
LDA.0
INCA
STA.0
BNC sbfsStepDone ; It did not wrap, so the high byte is untouched.
DECD.0
LDA.0
INCA
STA.0
sbfsStepDone:
RET
; The two byte number at DP0 becomes itself plus the one at DP2. Only memory changes, so
; it survives the return: a routine cannot hand back a pointer or a register.
sbfsAddWord:
INCD.0
INCD.2
LDA.0
LDB.2
CCF
ADD
MVQA
STA.0
DECD.0
DECD.2
LDA.0
LDB.2
ADD ; Carries in from the low half. Nothing between the two touches it.
MVQA
STA.0
RET
; Compares the two byte number at DP0 with the one at DP2. Q is zero if they are equal,
; and the Carry Flag is set if the one at DP0 is the smaller. Both come back, because
; neither Q nor the Status register is put back by a return.
sbfsCompareWord:
LDA.0
LDB.2
CCF
SUB ; The high bytes settle it unless they are the same.
BNQ sbfsCompareDone
INCD.0
INCD.2
LDA.0
LDB.2
CCF
SUB
sbfsCompareDone:
RET
; The byte at DP0 against the byte at DP2. Q is zero if they are the same.
sbfsSameByte:
LDA.0
LDB.2
XOR
RET
; ---- Making a directory ----
;
; DP0 names one. Q is zero if it was made.
;
; A directory costs ONE ENTRY AND NO BLOCKS AT ALL: its start, its block count and its tail
; all stay zero. That is what keeps the flat array of entries the whole allocation map,
; which is the thing this filesystem is built on - with files laid down contiguously, every
; block is inside some entry's range or it is not, and an entry with no range is in
; nobody's way.
sbfsMakeDir:
CALL sbfsWalkParent
BNQ sbfsMakeFailed
; Nothing of that name in there already. Two entries with one name in one directory is a
; directory that cannot be searched sensibly: a search answers with whichever it meets
; first, and the other becomes unreachable without ever having been deleted.
CALL sbfsScanFor
BRQ sbfsMakeFailed
; A scan that found nothing leaves the walk where it was, so SbfsAt still says where
; this is going. Walking the head again to be sure would put the head's last name back
; into SbfsWanted and undo the leaf.
; A free entry, found the same way creating a file finds one.
SETD.0 SbfsDirStart
SETD.1 SbfsBlock
CALL sbfsCopyWord
SETD.0 SbfsDirBlocks
INCD.0
LDA.0
SETD.1 SbfsLeft
STA.1
sbfsMakeBlock:
CALL sbfsReadBlock
BNQ sbfsMakeFailed
SETD.1 SbfsBuffer
CALL sbfsBufferOut
SETD.2 SbfsBuffer
INIA 0d8
SETD.1 SbfsCount
STA.1
sbfsMakeEntry:
LDA.2
INIB 0x01
AND
BRQ sbfsMakeFill ; This one is free.
DPUP.2 0d32
LDA.1
DECA
STA.1
BNA sbfsMakeEntry
SETD.0 SbfsBlock
CALL sbfsStepWord
SETD.1 SbfsLeft
LDA.1
DECA
STA.1
BRA sbfsMakeFailed ; The directory is full.
BRI sbfsMakeBlock
sbfsMakeFill:
PSHD.2
POPD.3
INIA 0x03
STA.3 ; In use, and a directory.
; No blocks, no start and no tail. Written out rather than left alone, because a free
; entry is not the only thing that lands here.
PSHD.3
POPD.1
INCD.1
INIB 0d5
sbfsMakeZero:
RSTA
STA.1
INCD.1
DECB
BNB sbfsMakeZero
PSHD.3
POPD.1
DPUP.1 0d28
SETD.0 SbfsAt
CALL sbfsCopyWord
PSHD.3
POPD.1
DPUP.1 0d06
SETD.0 SbfsWanted
INIA 0d22
SETD.2 SbfsCount
STA.2
sbfsMakeName:
LDA.0
STA.1
INCD.0
INCD.1
LDA.2
DECA
STA.2
BNA sbfsMakeName
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
BNQ sbfsMakeFailed
CALL sbfsRaiseVersion
RET
sbfsMakeFailed:
RSTA
INIB 0d1
CCF
ADD
RET
; The disk now has a directory on it, so it is a version two disk and has to say so.
;
; THIS IS THE ONLY THING THAT RAISES THE NUMBER, because it is the only thing that makes
; the difference between the two versions real. A disk stays readable by anything that has
; never heard of a directory right up until it actually has one.
sbfsRaiseVersion:
RSTA
SETD.0 SbfsBlock
STA.0
INCD.0
STA.0
CALL sbfsReadBlock
BNQ sbfsRaiseDone
SETD.1 SbfsBuffer
CALL sbfsBufferOut
SETD.0 SbfsBuffer
DPUP.0 0d04
INIA 0d2
STA.0
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
sbfsRaiseDone:
RSTA
RSTB
CCF
ADD
RET
; ---- Removing a directory ----
;
; DP0 names one. Q is zero if it went.
;
; ANYTHING STILL INSIDE IT IS A REFUSAL, and that is not politeness. A parent is an entry
; INDEX, and a freed index is handed straight to the next thing put on the disk - so the
; children of a directory removed from under them would turn up inside whatever took its
; place. Nothing points downward, so there would be no way to find them afterwards and no
; way to notice. Emptying it first is the only safe order there is.
sbfsRemoveDir:
CALL sbfsFind
BNQ sbfsRemoveFailed
SETD.0 SbfsFoundFlags
LDA.0
INIB 0x02
AND
BRQ sbfsRemoveFailed ; A file. Deleting is for those.
; Where it is, kept while the disk is asked whether anything lives in it - the asking
; reads other blocks and leaves the walk somewhere else entirely.
SETD.0 SbfsAt
SETD.1 SbfsHoldAt
CALL sbfsCopyWord
CALL sbfsHasChildren
BRQ sbfsRemoveFailed
; Found again, because looking for children read over the block the entry was in.
SETD.0 SbfsHoldAt
SETD.1 SbfsTarget
CALL sbfsCopyWord
SETD.0 SbfsTarget
CALL sbfsBackWord
CALL sbfsAtIndex
BNQ sbfsRemoveFailed
CALL sbfsWipeFound
RET
sbfsRemoveFailed:
RSTA
INIB 0d1
CCF
ADD
RET
; Q is zero if anything at all says its parent is SbfsHoldAt. Nothing points downward, so
; the only way to know what is in a directory is to ask everything whether it is in it.
sbfsHasChildren:
SETD.0 SbfsDirStart
SETD.1 SbfsBlock
CALL sbfsCopyWord
SETD.0 SbfsDirBlocks
INCD.0
LDA.0
SETD.1 SbfsLeft
STA.1
sbfsChildBlock:
CALL sbfsReadBlock
BRQ sbfsChildLoaded
RET ; The read failed, and Q says so - which reads as "yes", and
; refusing to remove something on a disk that will not read is the
; right way round to be wrong.
sbfsChildLoaded:
SETD.1 SbfsBuffer
CALL sbfsBufferOut
SETD.2 SbfsBuffer
INIA 0d8
SETD.1 SbfsCount
STA.1
sbfsChildEntry:
LDA.2
INIB 0x01
AND
BRQ sbfsChildNext
; Through a CALL, so that DP2 comes back on the entry without anything having to work
; out where that was. Doing the comparison in line here meant clobbering DP2 and then
; rebuilding it from the buffer and the count - which had the subtraction the wrong way
; round, walked the pointer off the end of the block, and let rmdir take a directory
; with something still in it. Exactly the failure this routine exists to prevent.
CALL sbfsMatchHold
BRQ sbfsChildYes
sbfsChildNext:
DPUP.2 0d32
SETD.1 SbfsCount
LDA.1
DECA
STA.1
BNA sbfsChildEntry
SETD.0 SbfsBlock
CALL sbfsStepWord
SETD.1 SbfsLeft
LDA.1
DECA
STA.1
BRA sbfsChildNone
BRI sbfsChildBlock
sbfsChildYes:
RSTA
RSTB
CCF
ADD ; Q is zero: something lives there.
RET
sbfsChildNone:
RSTA
INIB 0d1
CCF
ADD
RET
; ---- Deleting ----
;
; Frees a file. DP0 names it, and Q is zero if it went.
;
; A deleted entry and one that was never used are the same thing, which is the whole of
; what deleting is here: the entry is zeroed and its blocks stop being spoken for. THE
; BLOCKS THEMSELVES ARE LEFT EXACTLY AS THEY WERE, so what was in a file is still on the
; disk until something is put over the top of it. Worth knowing if anything is ever meant
; to be private. The host tool does the same, so the two agree about what a deleted disk
; looks like.
;
; Nothing is compacted. Deleting leaves a hole, and because files are contiguous a hole is
; only usable by something that fits inside it. That is the price of the directory being
; the whole allocation map, and tidying it up is an ordinary program somebody can write
; rather than anything the format has to say.
sbfsDelete:
CALL sbfsFind
BNQ sbfsDeleteFailed
; A DIRECTORY IS NOT DELETED HERE, AND THAT REFUSAL IS NOT POLITENESS. A parent is an
; entry index, and a freed index is handed straight to the next thing put on the disk -
; so the children of a directory wiped from under them would reappear inside whatever
; took its place. Nothing points downward, so there is no way to find them afterwards
; and no way to notice. Emptying it first is the only safe order there is.
SETD.0 SbfsFoundFlags
LDA.0
INIB 0x02
AND
BNQ sbfsDeleteFailed
CALL sbfsWipeFound
RET
; Throws away whatever the last find landed on, wherever it landed. DP3 is on the entry and
; SbfsBlock is the directory block it came out of, which is everything needed to change it
; and put it back.
;
; Removing a directory arrives here too. A directory has no blocks, so the count that goes
; back to the free total is nought and the sum is right without being a special case.
sbfsWipeFound:
; How much room it was taking, worked out before the entry that says so is thrown away.
CALL sbfsFileExtent
; sbfsFind leaves DP3 on the entry and SbfsBlock on the directory block it came out of,
; which is everything needed to change it and put it back.
PSHD.3
POPD.0
INIB 0d32
sbfsDeleteWipe:
RSTA
STA.0
INCD.0
DECB
BNB sbfsDeleteWipe
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
BNQ sbfsDeleteFailed
; And the free count goes back up. It is a note rather than the truth, but a note worth
; keeping right.
RSTA
SETD.0 SbfsBlock
STA.0
INCD.0
STA.0
CALL sbfsReadBlock
BNQ sbfsDeleteFailed
SETD.1 SbfsBuffer
CALL sbfsBufferOut
SETD.0 SbfsBuffer
DPUP.0 0d12
SETD.2 SbfsWantBlocks
CALL sbfsAddWord
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
RET
sbfsDeleteFailed:
RSTA
INIB 0d1
CCF
ADD
RET
; ---- Renaming ----
;
; DP0 is the name a file has, DP1 is the name it should have. Q is zero if it was renamed.
;
; A file keeps the directory it is in: only the twenty two bytes of the name change, and
; the parent is not among them. Moving something between directories is a different job
; and is not this one.
;
; Only the twenty two bytes of the name change, so no data moves and no block is touched
; but the one holding the entry. THAT IS WHAT MAKES A SAFE SAVE POSSIBLE. Writing a file
; that has grown means putting it somewhere else, and the obvious order - throw the old one
; away, then write the new one - loses the lot if there turns out to be nowhere to put it.
; Renaming is the cheapest thing this filesystem can do and the only one that can be left
; until last, so it is what the order is built around.
sbfsRename:
; Where the old name is, kept somewhere that finding things will not tread on.
SETD.2 SbfsSavedName
STD.0.2
; The new name is a path like any other, so only its last name is the name. Renaming
; something to "/A/notes.txt" used to call it that, all thirteen characters of it.
PSHD.1
POPD.0
CALL sbfsWalkParent
BNQ sbfsRenameFailed
SETD.0 SbfsAt
SETD.1 SbfsHoldAt
CALL sbfsCopyWord
SETD.0 SbfsWanted
SETD.1 SbfsNewName
CALL sbfsCopyName
; Refused if something already answers to that name in that directory. Two entries with
; one name in one place is a directory that cannot be searched sensibly: a search answers
; with whichever it meets first, and the other becomes unreachable without ever having
; been deleted.
CALL sbfsScanFor
BRQ sbfsRenameFailed
SETD.2 SbfsSavedName
LDD.0.2
CALL sbfsFind
BNQ sbfsRenameFailed
; RENAMING DOES NOT MOVE ANYTHING. Only the twenty two bytes of the name change, and the
; parent is not among them - so a new path naming a different directory would be a lie
; the disk went along with. Refused instead.
SETD.0 SbfsUpParent
SETD.2 SbfsHoldAt
CALL sbfsCompareWord
BNQ sbfsRenameFailed
; Not a directory. Renaming one would be safe enough, but the shell has no way to make
; one yet, so allowing it here would only be a way to reach something that cannot be
; got at any other way.
SETD.0 SbfsFoundFlags
LDA.0
INIB 0x02
AND
BNQ sbfsRenameFailed
PSHD.3
POPD.1
DPUP.1 0d06 ; Past the flags, the start, the block count and the tail.
SETD.0 SbfsNewName
INIA 0d22
SETD.2 SbfsCount
STA.2
sbfsRenameName:
LDA.0
STA.1
INCD.0
INCD.1
LDA.2
DECA
STA.2
BNA sbfsRenameName
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
RET
sbfsRenameFailed:
RSTA
INIB 0d1
CCF
ADD
RET
; ---- Writing a file a block at a time ----
;
; The mirror of reading one, and it needs something reading does not: state. A read is a
; whole question in itself - here is a name and an index, hand me that block - but a safe
; write cannot be, because the new file has to exist somewhere before the old one is thrown
; away, and something has to remember which temporary belongs to which name between one
; block and the next.
;
; ONE WRITE IS OPEN AT A TIME AND COSMOS HOLDS IT, rather than the program being handed
; something to keep. The careful order below is the one sbfsSaveFile uses and it is not
; obvious; leaving it to each program that streams would mean every one of them getting it
; right separately, and the cost of getting it wrong is somebody's file.
;
; sbfsStreamStart DP0 names it, SbfsFileBlocks and SbfsFileTail say how big
; sbfsStreamWrite DP1 is the block, SbfsIndex says which one it is
; sbfsStreamDone the temporary takes the name, and the old file goes
;
; NOTHING THAT ALREADY EXISTS IS TOUCHED UNTIL THE LAST OF THOSE. The room for the whole
; file is taken at the start, so a disk that cannot hold it says so while the old one is
; still there - which is better than the order sbfsSaveFile has to use, where the size is
; only known once the caller has the bytes in hand.
sbfsStreamStart:
; WHERE THE NAME IS, KEPT FIRST OF ALL. DP0 holds it on the way in and everything below
; wants DP0 for something else, so the pointer has to be put somewhere before the first
; of those - not after, which is a routine that walks whatever it last happened to point
; at and reports that it could find no room.
SETD.2 SbfsStreamPath
STD.0.2
; The size, put aside before anything walks the disk. Finding things overwrites the place
; a size is normally said, because finding describes whatever it last looked at.
SETD.0 SbfsStreamBlocks
SETD.2 SbfsFileBlocks
CALL sbfsSetWord
SETD.0 SbfsFileTail
LDA.0
SETD.1 SbfsStreamTail
STA.1
RSTA
SETD.0 SbfsStreamOpen
STA.0 ; Not open until it is.
SETD.2 SbfsStreamPath
LDD.0.2
CALL sbfsWalkParent
BNQ sbfsStreamNo
SETD.0 SbfsAt
SETD.1 SbfsStreamParent
CALL sbfsCopyWord
SETD.0 SbfsWanted
SETD.1 SbfsStreamLeaf
CALL sbfsCopyName
; Refused if that name belongs to a directory, and refused now rather than at the end
; with a written temporary nothing would ever come back for.
CALL sbfsStreamWhere
CALL sbfsScanFor
BNQ sbfsStreamFresh
SETD.0 SbfsFoundFlags
LDA.0
INIB 0x02
AND
BNQ sbfsStreamNo
sbfsStreamFresh:
; A temporary left by a stream that did not finish would be in the way, so it goes - but
; only if it really is one. See sbfsSaveFile: the flag says so and the name does not,
; because "sbfs.out" is a name somebody may have chosen for themselves.
CALL sbfsStreamTemp
CALL sbfsScanFor
BNQ sbfsStreamNoTemp
SETD.0 SbfsFoundFlags
LDA.0
INIB 0x04
AND
BRQ sbfsStreamNo ; Somebody's own file, under a name we wanted. Left alone.
CALL sbfsWipeFound
sbfsStreamNoTemp:
; And the room for all of it, taken while the old file is still safe.
SETD.0 SbfsFileBlocks
SETD.2 SbfsStreamBlocks
CALL sbfsSetWord
SETD.0 SbfsStreamTail
LDA.0
SETD.1 SbfsFileTail
STA.1
CALL sbfsStreamTemp
CALL sbfsCreateTempAt
BNQ sbfsStreamNo
; WHERE THE TEMPORARY BEGINS, KEPT NOW. Nothing moves a file once it is made, so every
; block after this one can be written without looking it up again. Finding it each time
; worked and was not even slow - a scan stops the moment it matches, and a temporary
; lands in an early slot - but it is a walk of the directory per block for an answer that
; cannot have changed, and on a disk whose early entries are all taken it would be a walk
; of the whole thing.
SETD.0 SbfsStreamAt
SETD.2 SbfsFileStart
CALL sbfsSetWord
INIA 0x01
SETD.0 SbfsStreamOpen
STA.0
RSTA
RSTB
CCF
ADD
RET
sbfsStreamNo:
RSTA
INIB 0d1
CCF
ADD
RET
; DP1 is the block and SbfsIndex says which one. The temporary is found again each time,
; because everything in between has been reading other blocks over the one it lives in.
sbfsStreamWrite:
SETD.0 SbfsStreamOpen
LDA.0
BRA sbfsStreamNo
; Where the file is and how big it is, said again rather than looked up: all three were
; settled when the temporary was made, and everything since has been describing whatever
; it last looked at.
SETD.0 SbfsFileStart
SETD.2 SbfsStreamAt
CALL sbfsSetWord
SETD.0 SbfsFileBlocks
SETD.2 SbfsStreamBlocks
CALL sbfsSetWord
SETD.0 SbfsStreamTail
LDA.0
SETD.2 SbfsFileTail
STA.2
CALL sbfsWriteOne
RET
; DP1 is where the block should go and SbfsIndex says which one. The other direction of
; sbfsStreamWrite, and the thing that lets a writer keep only ONE block of a file in hand:
; anything writing two parts of a file at once has to be able to put a block down, go
; somewhere else, and pick it up again where it left off.
sbfsStreamFetch:
SETD.0 SbfsStreamOpen
LDA.0
BRA sbfsStreamNo
SETD.0 SbfsStreamTo
STD.1.0
SETD.0 SbfsFileStart
SETD.2 SbfsStreamAt
CALL sbfsSetWord
SETD.0 SbfsFileBlocks
SETD.2 SbfsStreamBlocks
CALL sbfsSetWord
SETD.0 SbfsStreamTail
LDA.0
SETD.2 SbfsFileTail
STA.2
SETD.0 SbfsStreamTo
LDD.1.0
CALL sbfsReadOne
RET
; SbfsFileBlocks and SbfsFileTail say how big it turned out to be, which need not be how
; big it was started at.
;
; A WRITER MAY ASK FOR MORE ROOM THAN IT ENDS UP USING, and that is not laziness on its
; part. Some sizes are not knowable until the last byte is out: the assembler cannot say
; how many vectors a program installs until it has resolved them, and by then the file it
; is writing into must already exist. So the room is taken generously at the start, where
; running out costs nothing, and the size is told the truth here.
;
; The blocks that were asked for and not used go back to the free count. It is a note
; rather than the authority - the directory is - but a note worth keeping right, and two
; disks holding the same files must hold the same bytes.
sbfsStreamDone:
SETD.0 SbfsStreamOpen
LDA.0
BRA sbfsStreamNo
; What it really came to, put aside before anything walks the disk.
SETD.0 SbfsStreamNewBlocks
SETD.2 SbfsFileBlocks
CALL sbfsSetWord
SETD.0 SbfsFileTail
LDA.0
SETD.1 SbfsStreamNewTail
STA.1
; ---- MORE THAN WAS RESERVED IS REFUSED ----
;
; A writer may finish smaller than it asked for, which is the whole point of being told
; the size here. It may not finish BIGGER. The blocks after a file belong to whatever
; comes next, so an entry claiming more than was set aside for it claims somebody else's
; - and nothing anywhere would say so, because a directory entry is the only record of
; what a file owns. The count of free blocks would go wrong in the same breath, the
; subtraction below running backwards past zero.
;
; osFileWrite already refuses a block index past the end. This is the same bound from the
; other side, and it was missing: the index was checked because writing off the end was
; the obvious way to reach a neighbour, and committing a larger size reaches the same
; neighbour by simply claiming it.
;
; CHECKED BEFORE ANYTHING IS TOUCHED, which is why the temporary is found twice. The old
; file is deleted a few lines down, and a refusal after that point would have destroyed
; the thing it was protecting.
CALL sbfsStreamTemp
CALL sbfsScanFor
BNQ sbfsStreamNo
; What it was given, both halves of it.
SETD.0 SbfsStreamResBlocks
SETD.2 SbfsFileBlocks
CALL sbfsSetWord
SETD.0 SbfsFileTail
LDA.0
SETD.1 SbfsStreamResTail
STA.1
; And the room that came to, kept for the free count at the end.
CALL sbfsFileExtent
SETD.0 SbfsStreamSpare
SETD.2 SbfsWantBlocks
CALL sbfsSetWord
; THE SIZE IS COMPARED, NOT THE ROOM IT TAKES UP. Those are not the same question: one
; block and a tail occupies exactly what two whole blocks occupy, so a file reserving the
; first and committing the second claims no block it was not given - and still reports
; two hundred and forty six bytes more than were ever written to it, which are whatever
; the disk had there before. Bounding the blocks alone would have called that fine.
SETD.0 SbfsStreamResBlocks
SETD.2 SbfsStreamNewBlocks
CALL sbfsCompareWord
BRC sbfsStreamNo ; More whole blocks than it was given.
BNQ sbfsStreamFits ; Fewer, so the tail cannot matter.
SETD.0 SbfsStreamResTail
LDA.0
SETD.2 SbfsStreamNewTail
LDB.2
CCF
SUB
BRC sbfsStreamNo ; The same blocks, and a longer tail.
sbfsStreamFits:
; Now, and not before, the old one goes. It may not be there at all, which is what
; writing something for the first time looks like from here.
;
; The same two writes and the same gap between them as sbfsSaveFile has, and the same
; answer: what stops here is recoverable by hand and by nothing else. The free count
; goes back afterwards, and a machine stopping THERE only leaves the note wrong, which
; the directory can always settle.
CALL sbfsStreamWhere
CALL sbfsScanFor
BNQ sbfsStreamNoOld
CALL sbfsWipeFound
sbfsStreamNoOld:
; And the temporary takes its name and its true size, which together are the whole of
; what committing is. Found again, because deleting the old one read over the block it
; lives in.
CALL sbfsStreamTemp
CALL sbfsScanFor
BNQ sbfsStreamNo
; Finished: the flag goes down in the same block write that gives it its name and its
; size. Flat rather than cleared, for the reason sbfsSaveFile gives.
PSHD.3
POPD.1
INIA 0x01
STA.1
PSHD.3
POPD.1
DPUP.1 0d06
SETD.0 SbfsStreamLeaf
CALL sbfsCopyName
PSHD.3
POPD.1
DPUP.1 0d03
SETD.0 SbfsStreamNewBlocks
CALL sbfsCopyWord
PSHD.3
POPD.1
DPUP.1 0d05
SETD.0 SbfsStreamNewTail
LDA.0
STA.1
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
BNQ sbfsStreamNo
; And the difference goes back, which is what it was given less what it kept. That can
; no longer be negative: the check at the top refused the only case where it could.
CALL sbfsStreamSize
CALL sbfsFileExtent
SETD.0 SbfsStreamSpare
SETD.2 SbfsWantBlocks
CALL sbfsSubWord
RSTA
SETD.0 SbfsBlock
STA.0
INCD.0
STA.0
CALL sbfsReadBlock
BNQ sbfsStreamNo
SETD.1 SbfsBuffer
CALL sbfsBufferOut
SETD.0 SbfsBuffer
DPUP.0 0d12
SETD.2 SbfsStreamSpare
CALL sbfsAddWord
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
BNQ sbfsStreamNo
RSTA
SETD.0 SbfsStreamOpen
STA.0
RSTA
RSTB
CCF
ADD
RET
; The size the writer says it came to, put back where the extent arithmetic reads it from.
; Said again rather than kept, because finding anything overwrites those two: they are where
; a find describes whatever it last looked at.
sbfsStreamSize:
SETD.0 SbfsFileBlocks
SETD.2 SbfsStreamNewBlocks
CALL sbfsSetWord
SETD.0 SbfsStreamNewTail
LDA.0
SETD.1 SbfsFileTail
STA.1
RET
; The directory the file is going in, and the name it will end up under. Said again before
; each step, because every step goes to the disk and leaves the walk somewhere else.
sbfsStreamWhere:
SETD.0 SbfsStreamParent
SETD.1 SbfsAt
CALL sbfsCopyWord
SETD.0 SbfsStreamLeaf
SETD.1 SbfsWanted
CALL sbfsCopyName
RET
; The same directory, under the name a half written file is kept as. Its own rather than
; the one a whole file save uses, so that neither can ever be handed the other's.
sbfsStreamTemp:
SETD.0 SbfsStreamParent
SETD.1 SbfsAt
CALL sbfsCopyWord
SETD.0 SbfsStreamName
SETD.1 SbfsWanted
CALL sbfsKeepName
RET
; ---- Saving over something that is already there ----
;
; DP0 names the file, DP1 is the data, and SbfsFileBlocks with SbfsFileTail say how big it
; now is. Q is zero if it was saved.
;
; This is the routine every tool that edits a document wants, and the reason it is here
; rather than in each of them is that the careful order is not obvious and getting it wrong
; destroys somebody's work:
;
; make a temporary nothing is lost if there is nowhere to put it
; write it
; delete the original only once the new one is safely down
; rename the temporary
;
; The obvious order - delete, create, write - looks fine and is a trap. Files here are
; contiguous, so a file that has grown may not fit where it was, and a create can be
; refused for want of a run long enough even on a disk with plenty of free blocks. Do it
; that way round and the original is already gone when that happens.
sbfsSaveFile:
SETD.2 SbfsSaveName
STD.0.2
SETD.2 SbfsSaveData
STD.1.2
; How big it is, kept aside: finding and deleting things both overwrite the place the
; size is normally said, because both of them describe whatever they last looked at.
SETD.0 SbfsSaveBlocks
SETD.2 SbfsFileBlocks
CALL sbfsSetWord
SETD.0 SbfsFileTail
LDA.0
SETD.1 SbfsSaveTail
STA.1
; WHERE IT GOES, WORKED OUT ONCE. Everything below is done in terms of a directory and
; a name rather than a path, and that is what makes the careful order below work in a
; subdirectory: the temporary has to be made in the SAME directory as the file, because
; the rename at the end changes a name and does not move anything.
SETD.2 SbfsSaveName
LDD.0.2
CALL sbfsWalkParent
BNQ sbfsSaveFailed
SETD.0 SbfsAt
SETD.1 SbfsSaveParent
CALL sbfsCopyWord
SETD.0 SbfsWanted
SETD.1 SbfsSaveLeaf
CALL sbfsCopyName
; Refused up front if that name belongs to a directory. Left to itself the delete below
; would refuse it, the rename at the end would refuse it too, and the save would fail
; then instead, having already written a temporary nothing would ever come back for.
CALL sbfsSaveWhere
CALL sbfsScanFor
BNQ sbfsSaveNotThere
SETD.0 SbfsFoundFlags
LDA.0
INIB 0x02
AND
BNQ sbfsSaveFailed
sbfsSaveNotThere:
; A temporary left behind by a save that did not finish would be in the way, so it goes.
;
; WHAT MAKES IT ONE IS THE FLAG AND NOT THE NAME. "sbfs.part" is a name a person is
; perfectly entitled to give a file of their own, and this used to delete whatever
; answered to it - so saving anything at all, once, quietly destroyed that file. The
; entry now says what it is, and something that is not ours stops the save instead.
CALL sbfsSaveTemp
CALL sbfsScanFor
BNQ sbfsSaveNoTemp
SETD.0 SbfsFoundFlags
LDA.0
INIB 0x04
AND
BRQ sbfsSaveFailed ; Somebody's own file, under a name we wanted. Left alone.
CALL sbfsWipeFound
sbfsSaveNoTemp:
SETD.0 SbfsFileBlocks
SETD.2 SbfsSaveBlocks
CALL sbfsSetWord
SETD.0 SbfsSaveTail
LDA.0
SETD.1 SbfsFileTail
STA.1
CALL sbfsSaveTemp
CALL sbfsCreateTempAt
BNQ sbfsSaveFailed
SETD.2 SbfsSaveData
LDD.1.2
CALL sbfsWriteFile
BNQ sbfsSaveFailed
; Now, and not before, the old one goes. It may not be there at all, which is what
; saving something for the first time looks like from here.
;
; EVERYTHING ABOVE THIS POINT CAN FAIL AND COST NOTHING. Below it there are two block
; writes and a gap between them, and a machine that stops in that gap has deleted the
; old file and not yet named the new one. The bytes are all there under the temporary's
; name and one rename gets them back, but nothing does that automatically and nothing
; here claims to: this is safe against the ways a save fails while it is running, not
; against the machine stopping. Closing the gap wants a journal, which is a great deal
; of disk to buy back two writes.
CALL sbfsSaveWhere
CALL sbfsScanFor
BNQ sbfsSaveNoOld
CALL sbfsWipeFound
sbfsSaveNoOld:
; And the temporary takes its name. Found again first, because everything above has been
; reading other blocks over the one it lives in.
CALL sbfsSaveTemp
CALL sbfsScanFor
BNQ sbfsSaveFailed
; FINISHED, WHICH IS THE FLAG AND THE NAME TOGETHER. Written flat rather than by
; clearing the one bit: a temporary is a file, so in use is the only other thing it can
; ever have been, and the whole byte is known.
PSHD.3
POPD.1
INIA 0x01
STA.1
PSHD.3
POPD.1
DPUP.1 0d06
SETD.0 SbfsSaveLeaf
CALL sbfsCopyName
SETD.1 SbfsBuffer
CALL sbfsBufferIn
CALL sbfsWriteBlock
RET
; The directory the file is going in, and the name it is going under. Said again before
; each step, because every step in between goes to the disk and leaves the walk somewhere
; else entirely.
sbfsSaveWhere:
SETD.0 SbfsSaveParent
SETD.1 SbfsAt
CALL sbfsCopyWord
SETD.0 SbfsSaveLeaf
SETD.1 SbfsWanted
CALL sbfsCopyName
RET
; The same directory, under the name the half finished file is written as.
sbfsSaveTemp:
SETD.0 SbfsSaveParent
SETD.1 SbfsAt
CALL sbfsCopyWord
SETD.0 SbfsTempName
SETD.1 SbfsWanted
CALL sbfsKeepName
RET
sbfsSaveFailed:
RSTA
INIB 0d1
CCF
ADD
RET
#Data
SbfsMagic:
"SBFS"
SbfsDirStart:
0x00 0x00
SbfsDirBlocks:
0x00 0x00
SbfsFileStart:
0x00 0x00
SbfsFileBlocks:
0x00 0x00
SbfsFileTail:
0x00
SbfsBlock:
0x00 0x00
SbfsDiskBlocks:
0x00 0x00
SbfsWantBlocks:
0x00 0x00
SbfsCandidate:
0x00 0x00
SbfsCandEnd:
0x00 0x00
SbfsEntryStart:
0x00 0x00
SbfsEntryEnd:
0x00 0x00
SbfsScratch:
0x00 0x00
SbfsOne:
0x00 0x01
SbfsCount:
0x00
SbfsMatchLeft:
0x00
SbfsLeft:
0x00
; ---- Where the machine is ----
;
; The working directory, written the way a parent is written: an entry index plus one, so
; zero is the root and a freshly booted machine is already there. A path that does not
; begin with a separator is measured from here.
;
; It lives here rather than in the shell because it is what a relative path MEANS, and the
; thing that resolves a path is here. Keeping it in the shell would mean either handing it
; down on every call or having the shell paste it onto the front of every name, and the
; second of those is how a name that is already absolute gets ruined.
SbfsCwd:
0x00 0x00
; ---- What walking a path keeps ----
;
; SbfsAt is where the walk has got to, written the way a parent is written: an entry index
; plus one, so that zero is the root and a version one disk's zeroes already say it.
SbfsPathAt:
0x00 0x00
; ---- What splitting a path off its last name keeps ----
SbfsHead:
#Reserve 0d96
SbfsHeadLen:
0x00
SbfsHoldAt:
0x00 0x00
; The last name of a path, kept out of the way while the rest of the path is walked.
SbfsLeaf:
#Reserve 0d23
SbfsSpanAt:
0x00
SbfsPathState:
0x00
SbfsPathLeft:
0x00
SbfsAt:
0x00 0x00
SbfsScanIndex:
0x00 0x00
; ---- What the disk's one buffer holds, or is about to ----
SbfsBufferBlock:
0x00 0x00
SbfsBufferKnown:
0x00
SbfsAheadIndex:
0x00 0x00
SbfsTarget:
0x00 0x00
SbfsUpParent:
0x00 0x00
SbfsFoundFlags:
0x00
; What the next entry made is to be marked with. sbfsCreateAt sets it to a plain file and
; sbfsCreateTempAt to a temporary, so it is never read without having just been written.
SbfsMakeFlags:
0x00
; Whether what is in SbfsFileStart and the rest really describes where the walk is now.
; Going up leaves them describing the entry it came from, and only the end of a path is
; close enough to care.
SbfsFieldsValid:
0x00
SbfsIndex:
0x00 0x00
; ---- What a walk through the directory keeps between calls ----
SbfsWalkBlock:
0x00 0x00
SbfsWalkLeft:
0x00
SbfsWalkCount:
0x00
SbfsWalkPointer:
0x00 0x00
SbfsWalkAt:
0x00 0x00
; Twenty three bytes for a name of twenty two, so that the last one is a zero nothing
; ever writes over and the name is always a string.
SbfsName:
#Reserve 0d23
SbfsWanted:
#Reserve 0d22
; ---- What renaming and saving keep ----
; A name on its way into an entry, padded to the twenty two bytes an entry holds.
SbfsNewName:
#Reserve 0d22
; Where a name lives, kept across a search, which needs the pointers for itself.
SbfsSavedName:
0x00 0x00
SbfsSaveName:
0x00 0x00
SbfsSaveData:
0x00 0x00
SbfsSaveBlocks:
0x00 0x00
SbfsSaveTail:
0x00
SbfsSaveParent:
0x00 0x00
SbfsSaveLeaf:
#Reserve 0d23
; What a document is called while it is being written and is not yet the real thing. A
; name nothing else is likely to want, and short enough to leave room for a long one.
SbfsTempName:
"sbfs.part"
; ---- What a file being written a block at a time keeps ----
SbfsStreamOpen:
0x00
SbfsStreamPath:
0x00 0x00
SbfsStreamFrom:
0x00 0x00
SbfsStreamTo:
0x00 0x00
SbfsStreamNewBlocks:
0x00 0x00
SbfsStreamNewTail:
0x00
SbfsStreamSpare:
0x00 0x00
SbfsStreamResBlocks:
0x00 0x00
SbfsStreamResTail:
0x00
SbfsStreamAt:
0x00 0x00
SbfsStreamParent:
0x00 0x00
SbfsStreamLeaf:
#Reserve 0d23
SbfsStreamBlocks:
0x00 0x00
SbfsStreamTail:
0x00
SbfsStreamName:
"sbfs.out"
SbfsBuffer:
#Reserve 0d256
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