SchFS is a 64-bit format addressing 64 ZB. The stack under it was not,
and the lowest limit was three orders of magnitude below the one anybody
would have guessed:
ide.c panicked on any block >= FSSIZE -- 150000 blocks, 614 MB
ide.c computed the sector in an int, and addressed it with LBA28
bio.c took a 32-bit block number, capping any device at 16 TB
schfs refused blocks past 0xffffffff, mirroring the cache
The FSSIZE check is the one that mattered. FSSIZE describes the size of a
v1 filesystem *image*; it had no business bounding a physical device, and
it meant a disk larger than half a gigabyte panicked the kernel rather
than being read.
struct buf's blockno is uint64 now, and so is bread's. idestart computes
the sector in 64 bits and picks LBA48 when it does not fit in 28 -- per
request, so everything that fits stays on the LBA28 path every existing
image has been read through. The 48-bit registers are written high half
first, because each is a two-deep FIFO and the other order leaves the
drive addressing whatever the low bytes alone describe.
Verified with a 2 GB disk carrying a marker at 1 GiB -- block 262144,
well past the old panic at 150000. The guest reads it back:
"MARKER-PAST-THE-OLD-LIMIT". schfs-check passes including the round-trip;
bootcheck 108 [ok].
Two limits deliberately left, both noted rather than guessed at: raw
/dev/hdN access still goes through devsw's 32-bit offset, so a raw device
is addressable to 4 GB; and usb_storage computes a 32-bit LBA, which is
what SCSI READ(10) carries -- READ(16) is a different command, not a
wider variable.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Two bugs reported from actual use, plus a test harness that had stopped
testing.
init could be killed by Ctrl-C, taking the machine with it. SIGINT goes
to the foreground process group, init is pgid 1, and any window where
tty_fg_pgrp is 1 -- before a shell claims the terminal, after one exits,
or between the two while the key is held -- lands it on init. init has
no handler, so killed was set, exit() ran, and exit() panics outright on
initproc. Spamming Ctrl-C at a frozen program is exactly the input that
finds that window. POSIX and Linux both discard a default-action signal
for pid 1; init_ignores() now does the same, SIGKILL included, because
init is not killable from userspace on any Unix.
Everything was slow because BSIZE was 1024 while a SchFS block is 4096,
so every block cost four IDE requests, each with its own interrupt and
sleep/wakeup. exec() of the 800 KB toybox binary meant ~800 round trips.
The giveaway: `seq 1 200`, which touches no file and prints nothing,
cost the same 2.0s as `cat /bin/toybox`, and `ls | wc -l` cost exactly
double -- both dominated by loading the same binary twice.
BSIZE is 4096 now, one request per SchFS block, and NBUF is 256 blocks
(1 MB) rather than 90 KB -- smaller than the binary every command execs,
so nothing was ever still resident. ideinit() issues SET MULTIPLE MODE,
which is what makes a 4096-byte transfer legal: READ/WRITE MULTIPLE move
the drive's multiple count per interrupt and nothing had ever set it,
which is the real reason idestart() carried a sector_per_block > 7 panic.
seq 1 200 2.02s -> 0.06s
ls /bin 2.76s -> 0.68s
ls /bin | wc -l 4.68s -> 0.73s
And the harness. bootcheck called Find-Qemu from a param() default,
which is bound before any function in the body exists -- so it died on
its first line and printed an error containing neither "FAIL" nor
"Exception", the two things being grepped for. It had not run since it
was made host-portable. Worse, an earlier index-based edit had deleted
the Expect blocks for -Tty, -Usb, -Sock, -Ps and -Evdev, so five of the
seven modes asserted nothing at all. Restored, and the USB run gets its
own 16 MB build/usbstick.img: it had been pointed at build/fs.img, which
nothing builds since SchFS became root, so QEMU refused to start.
242 checks across seven modes, all passing, and make schfs-check green.
An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.
No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.
