Nexoniarz is the sole author and SchOS was never published under
Apache-2.0, so this is a straight relicence. LICENSE is the FSF GPLv2 text,
every first-party SPDX header moves to GPL-2.0-or-later, and NOTICE,
README.md, docs/licensing.md and the site say so. projects/schfs-linux
follows the rest of the tree.
The GPL gives copyleft: a fork has to ship its source. It also lifts the
old "Linux drivers, never" rule, since GPL-2.0-only code combines with
GPL-2.0-or-later. "Or later" leaves room for GPLv3, but one binary still
has to pick one version, so docs/licensing.md now keeps Apache-2.0 and
GPLv3 code out of the kernel to keep Linux code possible there. BSD
4-clause code goes from "avoid" to "no", because the advertising clause
is GPL-incompatible.
LDLS still ships no .ko. That boundary is now project policy rather than
a legal requirement, and ldls.md, devices.md and licensing.md section 6
say so. refmod declares license=GPL, and ldls-check passes (27 checks).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Gate 1, item 3, and the last of foundations.md.
bind() creates a T_SOCK node at the path; connect() resolves the path and looks
for the socket bound to **that inode**. Matching on the inode rather than on
the path *string* is the part that matters: the name used to live only in the
socket table, so two spellings of one path missed each other, a relative path
never matched an absolute one, and there was nothing to stat() or unlink().
An inode is the thing a path resolves *to*, so connect() can walk the path
however it likes and arrive at the same socket.
# ls -l /tmp
srwxr-xr-x 1 root root 0 2026-09-22 08:04 socktest
The node is a marker, not the binding. It holds no data and the live
association stays in the socket table, so a socket file left by a crash is
what Linux leaves behind -- a dead file that connect() refuses until something
binds again -- and unlink()ing a live socket's path does not disturb anyone
already connected.
EADDRINUSE comes from the *directory* rather than from a scan of the table,
deliberately: a stale socket file has to refuse a rebind for the same reason a
running server's does, or two servers both believe they own it. The creation
lives in sys_bind() and not in unix.c, because that is the layer with both --
kernel/net/unix.c knows about sockets and has no business calling create().
T_SOCK is a compat addition to SchFS by the rule in schfs.h: a driver that does
not know SCHFS_T_SOCK maps it to a zero-length regular file, so nothing goes
stale and nothing becomes unreadable.
cmd/socktest section 15 asserts the plan's own wording -- bind, stat, see an
`s`, unlink -- plus the two a name table could never fail: a second bind to a
live path is refused, and connecting to a path that is a *regular file* is
refused rather than matched by name.
**And the semantics being real broke socktest on its second run**, correctly:
the socket files persisted and every bind() hit EADDRINUSE. Every real server
unlinks before binding; socktest now does too, which is the change the new
behaviour demands rather than a workaround for it.
Chasing that turned up something worse. `socktest` reported rc=1 with every
check passing, and so did every other first-party program:
- **lib/start.S called main and threw %eax away.** sys_exit() reads the
status from %rdi and nothing put it there, so every program exited with
whatever that register happened to hold. Every test suite ends in
`return failures ? 1 : 0` and none of it reached the shell.
- **exit(void) passed no status either**, for the same reason: the
declaration takes no argument, so %rdi was the caller's litter.
`if socktest; then` works now, and a failing command reports 1 -- checked both
ways, because a fix that makes everything return 0 would look identical from
the success side.
Also factored: unlink_path() out of sys_unlink, so a failed bind can take its
own node back out without going through the syscall entry, and create_sock()
as a named door rather than exporting create() with an arbitrary type.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The last three phases of the filesystem, which were written together and
touch the same files throughout -- kmount.c, objw.c and vfs.c are each
rewritten by all three -- so they land as one commit rather than three
that could not be built separately.
Durability. A transaction that reaches the platter out of order is worse
than one that never reached it: the uberblock can name a tree whose
blocks are still in the drive's write cache. bdirty/bflush give the
buffer layer an explicit barrier, ideflush issues ATA FLUSH CACHE and
usb_storage_flush the SCSI SYNCHRONIZE CACHE that means the same thing,
and a commit now waits for the data before it writes the root that
points at it. The uberblock groups are read newest-first with fallback,
so a volume whose newest roots are torn mounts at an older one and says
which generations were lost.
Reflink. Extents carry a refcount, so two objects can name the same
blocks and neither frees them while the other holds them. Exposed as
FICLONE -- Linux's ioctl value, so `cp --reflink` works unmodified --
and as cmd/reflink for the case where there is no cp to hand.
Attributes, and the one genuinely new idea here. attr.c stores named
values on an object, reachable through setxattr/getxattr/removexattr at
Linux's syscall numbers. On top of that, schfs_index declares an index
over an attribute name and schfs_query answers "which objects carry this
value" from the B-tree rather than by walking. A query against an
unindexed attribute is refused with an error, never silently answered by
a full scan: a query that quietly becomes a scan is worse than one that
admits it cannot help. cmd/schattr drives both.
Three bugs fixed on the way, each found by the numbers being wrong
rather than by inspection:
- statfs's f_fsid was declared int64[2]. Linux's fsid_t is two *ints*,
so every field after it landed one slot late: userland read f_frsize
out of f_namelen, got 255, and df reported a 32 MB root filesystem
as 1992 KB. It hid for as long as it did because the fields used to
be invented constants, so wrong numbers looked like the usual ones.
- struct inode's nlink was a short against SchFS's uint32, so a file
past 32767 names came back negative -- and iput frees an object
whose count reaches zero. It is an int now, signed on purpose, so an
underflow lands somewhere a check can see rather than wrapping.
- filewrite split every write to fit v1's log. That limit belongs to
the journal, not to writing, and SchFS makes one transaction of
whatever it is handed: a 1 MB write was becoming 170 commits and
170 flushes for nothing. fs_ops carries max_write now, and SchFS
sets no limit.
Also here: a real mount table, so `mount -t schfs /dev/hdb /mnt` shows
up in /proc/mounts -- df looks a path up there before it calls statfs at
all, so a mount missing from that list was invisible to it -- several
volumes mounted at once, snapshots mounted by name, and /proc/fsstat
with an rdtsc-based counter, which is the only instrument fine enough to
see inside a single syscall.
Verified: `make schfs-check` passes in full, including the sweep that
crashes the volume at each of 119 points mid-transaction and requires
every one to mount with exactly its committed data, and the case where
both newest uberblocks are rubbish and the volume still comes back. The
headless boot check passes with 27 [ok] and no failures, on a SchFS root.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Two loose ends from the mount-by-name commit, both closed.
A slot is a device number, so supporting more than one snapshot is a
small array rather than a redesign: SCHFS_SNAP_DEV through
SCHFS_SNAP_DEV + SCHFS_SNAP_SLOTS - 1, each with its own volume and its
own scratch pages, allocated on first use. Four of them -- "one at a
time" is an odd thing to have to explain, and the cost is two pages per
slot. Not many, because each one is a device number and those are a
small fixed space.
The leak mattered more. umount removed the mount table entry and left the
slot marked in use, so a snapshot could be unmounted and then never
mounted again until reboot. sys_umount2 releases it now, keyed off the
device it already has in hand.
Verified in the running system: two snapshots mounted at once, both
readable, both unmounted, and a third mount afterwards succeeds and reads
correctly -- which is the case that failed before.
schfs-check passes; bootcheck 108 [ok].
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
`mount -t schfs @golden /mnt` mounts a snapshot. The source argument
finally means something: sys_mount ignored it outright, because there was
one volume and nothing to choose between. `@name` rather than a path
because a snapshot is not a device -- there is no node in /dev for it and
there should not be, since it lives inside the volume already mounted.
A second volume rather than a parameter threaded through all 23 schfs_k*
entry points. Only the read side can ever address it, so the write path
keeps talking to the live volume and needed no change; the four read
entry points grew _dev variants and pick the volume from the device the
inode already carries. One fs_ops table serves both, because every entry
takes an inode and dispatches on it -- a second table would be the same
pointers under a different name.
It needs its own device number: a snapshot's object ids are the *same
numbers* as the live tree's, so one device would make the two views alias
in the inode cache and hand a reader whichever was cached first.
Three things this turned up, none of them new but all of them reachable
for the first time:
- sys_mount refused with `dev == SCHFS_DEV`, meaning "do not mount SchFS
onto SchFS". A snapshot's mount point is necessarily on the live root,
so that refused the entire feature. The real condition is mounting a
device onto *itself*, which is `dev == fsdev`.
- createat allocates an inode and then panics if dirlink fails --
reasonable about a writable filesystem, a crash on a read-only one.
The refusal now happens before anything is allocated. Unlink and
rename already handled a refusal properly.
- a refused create reported ENOENT, so writing to a snapshot said "No
such file or directory" -- the sentence a shell prints for every
create failure. It reports EROFS now.
Verified in the running system against an image built with
--snapshot golden: the mount succeeds, ls lists the snapshot's tree,
/mnt2/etc/motd reads back through it, and a write is refused with
"Read-only file system".
One at a time, and no umount path for it yet: mount_del_by_root removes
the mount table entry, but ksnap_unmount is only called on the failure
paths. schfs-check passes; bootcheck 108 [ok].
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
BOUNCE was 2048 while the comment directly above it said "one page at a
time", and the buffer it sizes is a single kalloc() -- so half of every
bounce buffer went unused and every read did twice the work it needed to.
The chunk size is not a copy-size tuning knob. Each trip through the loop
takes the volume sleeplock and builds a fresh B-tree cursor to find the
extent for that offset, so it really sets how many tree descents happen
per byte read. An 834 KB file took 417 of them; it now takes 209.
Measured in the guest, bracketed inside one command line so nothing
depends on host timing: reading 834 KB goes from 1.73s to 0.90s under
TCG, cold and warm alike. Warm equalling cold is itself the tell -- the
cost was never the disk, it was the per-chunk work, which is why KVM was
6.4x faster on the same read while caching made no difference at all.
This does not fix `ls`, and the numbers say why: 2.80s -> 2.65s cold.
loaduvm already reads a page at a time, so exec was never the bottleneck
there. At 241 entries in 2.65s that is ~11ms per file, spent in the
per-entry lookup path rather than in reading anything.
schfs-check passes; bootcheck 108 [ok].
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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.
