Re: [PATCH 0/2] fs: honor FOP_UNSIGNED_OFFSET in llseek and positional I/O

[Stian Halseth]

Ping. The series still applies cleanly to current master (7.3-rc7).

Since posting it has run on an UltraSPARC T4-1 (7.2.y) and a SPARC T7-1
(7.3-rc5) as the production kernel for a month. Is there anything you
would like changed before it can be picked up?

https://lore.kernel.org/linux-fsdevel/20260917151614.376867-1-stian@xxxxxx/

/Stian

On Thu, 2026-09-17 at 17:16 +0200, Stian Halseth wrote:
> Two generic VFS bugs found while fixing pldd(1) on sparc64, where
> userspace is mapped above 2^63 so file positions on /proc/PID/mem
> have
> the top bit set.
> 
> FOP_UNSIGNED_OFFSET declares a file's offsets unsigned, and
> vfs_llseek(),
> rw_verify_area() and the mmap path honor it.  Two sets of syscall
> wrappers do not:
> 
>   1. sys_llseek() takes a negative result from vfs_llseek() for an
> error
>      and returns it truncated to int without filling *result.
>   2. pread64/pwrite64/preadv/pwritev reject a negative position
> before
>      looking up the file.
> 
> Both patches only change behavior for a file with FOP_UNSIGNED_OFFSET
> and a position with the top bit set.  Today that is /proc/PID/mem,
> /dev/mem, the sparc ADI driver and the DRM/accel device files; for
> all
> of them lseek() followed by read() at that position already works, so
> the wrappers now match it.
> 
> Tested on an UltraSPARC T4: pread(), preadv(), pwrite(), pwritev()
> and
> lseek() on /proc/PID/mem at positions above 2^63 return the correct
> data
> and offset; a negative position on a regular file or a pipe still
> fails
> with EINVAL and position 0 on a pipe with ESPIPE, as before; and the
> stock pldd(1) works again.  On other architectures the change is a
> no-op
> for every file without FOP_UNSIGNED_OFFSET, and userspace addresses
> never set the top bit, so the new paths are only reachable by passing
> a bogus position to /proc/PID/mem or /dev/mem, which then fails in
> the
> driver instead of the wrapper.
> 
> The glibc side is
> https://sourceware.org/bugzilla/show_bug.cgi?id=34641;
> 
> Stian Halseth (2):
>   fs: fix llseek() result for files with unsigned offsets
>   fs: allow positional I/O on files with unsigned offsets
> 
>  fs/read_write.c | 38 +++++++++++++++++++-------------------
>  1 file changed, 19 insertions(+), 19 deletions(-)
>

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