9p: invalidate readdir buffer on seek

The per-fid readdir buffer (fid->rdir) is populated lazily and only
refilled when fully drained (rdir->head == rdir->tail). userspace
lseek() on a directory fd updates file->f_pos via generic_file_llseek()
but does not touch the cached buffer, so the next getdents() iterates
the stale cache and emits entries from the previous position instead
of the one the caller asked for.

Track the file position the cached data corresponds to in
struct p9_rdir, and drop the cache on entry to iterate_shared when it
no longer matches ctx->pos. The 9p protocol's Tread/Treaddir already
take an arbitrary offset on every request, so a refill at the new
position is always legal; no .llseek override or seek restriction is
needed.

Reported-by: Pierre Barre <pierre@barre.sh>
Link: https://lore.kernel.org/v9fs/496d10b9-40fe-4f81-8014-37497c37ff63@app.fastmail.com/
Signed-off-by: Pierre Barre <pierre@barre.sh>
Message-ID: <20260512132032.369281-2-pierre@barre.sh>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

0 files changed, 0 insertions, 0 deletions