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os: fdtable: restore errno if optional locking ioctl fails

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The `zvfs_finalize_typed_fd()` function notifies some backends
via `ioctl()` with `ZFD_IOCTL_SET_LOCK`. However, support for
this method and functionality is optional.

In backends that do not support locking, this benign failure can
set `errno` to 95 (`EOPNOTSUPP`) in many circumstances where a
change in `errno` (indicating some kind of failure) is not
appropriate.

Prevent errno poisoning by backing-up and restoring `errno`.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>
This commit is contained in:
Chris Friedt 2024-12-28 13:11:25 -05:00 • committed by Henrik Brix Andersen
commit 2a2806bb40
1 changed files with 6 additions and 0 deletions
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6
lib/os/fdtable.c
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@ -280,8 +280,14 @@ void zvfs_finalize_typed_fd(int fd, void *obj, const struct fd_op_vtable *vtable
* variables to avoid keeping the lock for a long period of time.
*/
if (vtable && vtable->ioctl) {
int prev_errno = errno;
(void)zvfs_fdtable_call_ioctl(vtable, obj, ZFD_IOCTL_SET_LOCK,
&fdtable[fd].lock);
if ((prev_errno != EOPNOTSUPP) && (errno == EOPNOTSUPP)) {
/* restore backed-up errno value if the backend does not support locking */
errno = prev_errno;
}
}
}