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Work across two disks: copy between them, and run a program from one on

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files from the other

Two things anybody expects of a second disk, and each needed something
different.

COPYING NEEDED TWO THINGS TO REMEMBER A DRIVE.

The write stream is the only thing here that lives across service calls, so
it is the only thing whose drive can change underneath it: every
osFileBlock names its source path again and goes back to the source drive,
and then osFileWrite has to come home. It records the drive it was opened
on and returns there.

And the file lookup CACHE. It keeps the last path resolved so a reader
walking a file does not re-walk the directory for every block - and
skipping the walk skipped the drive the path named, so block one of a
cross-drive copy read the source's block numbers off the DESTINATION disk.
It only showed on files of more than one block, because a file of one is
never looked up twice. One block worked and two did not, which is a
suspicious enough shape to have suspected sooner.

RUNNING A PROGRAM FROM ELSEWHERE NEEDED A THIRD PLACE TO LOOK, and two
restorations.

The shell tried where you are and /Apps on the disk you are on. It now
tries /Apps on drive 0 as well, which is what makes the system's programs
work from a disk of your own - one with your files on it and no system,
which is most of the point of having a second disk.

The drive goes back after the load, because by then the program is in
memory and the blocks it came from mean nothing; and again when it exits,
because a program that copies between disks moves the drive as its own
paths need to and being left wherever it finished is not what was asked
for. Copy 1:/a 0:/b now leaves you exactly where you were.

The fixture disk grew an /Apps, because it kept its programs at the root
and so could not exercise the third place at all.

Two hours of the debugging above were spent on a stale disk image. The
machine boots the system that is ON the image, so a rebuilt cosmos.bin
means nothing until the image is rebuilt too - and the trace said my new
code never ran, which was true. Third time this project has been misled by
one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
This commit is contained in:
Anachronaut
2026-08-31 16:14:53 -04:00
co-authored by Claude Opus 5
parent 4cc6393f5b
commit e4f4bae762
12 changed files with 223 additions and 21 deletions
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Tests/manifest
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@@ -824,6 +824,20 @@ cosmosDrives | CosmOS/Source/cosmos.asm | run | cosmosDri
# system arrives, so it works for anything that takes one. A name beginning with a digit is
# still a name: the colon is the whole of what tells the two apart.
cosmosDrivePath | CosmOS/Source/cosmos.asm | run | cosmosDrivePath.in | 60000000 | disks/cosmos.img+disks/other.img
# ---- Working across two disks ----
#
# The two things anybody expects of a second disk: copying to it, and running a program that
# lives on one disk over files that live on the other.
#
# THE FILE IS MORE THAN ONE BLOCK ON PURPOSE. A copy of a single block looks its source up
# once and never meets the cache that skips the walk - and skipping the walk skipped the
# drive, so block one of every cross-drive copy came off the destination. One block worked
# and two did not.
#
# Say lives in /Apps on drive 0 and is run while standing on drive 1, which is the third
# place the shell looks. The drive it says afterwards is the check that fetching a program
# did not move the person who ran it.
cosmosCrossDisk | CosmOS/Source/cosmos.asm | run | cosmosCrossDisk.in | 90000000 | disks/cosmos.img+disks/other.img
printDecimalTest | testPrograms/printDecimalTest.asm | xfail | - | -
printDigitTest | testPrograms/printDigitTest.asm | xfail | - | -
printHexTest | testPrograms/printHexTest.asm | xfail | - | -