On Wednesday, March 19, 2025 11:08:58 AM CET Christian Schoenebeck wrote:
> According to 'man 2 close' errors returned by close() should only be used
> for either diagnostic purposes or for catching data loss due to a previous
> write error, as an error result of close() usually indicates a deferred
> error of a previous write operation.
>
> Therefore not decrementing 'total_open_fd' on a close() error is wrong
> and would yield in a higher open file descriptor count than actually the
> case, leading to 9p server reclaiming open file descriptors too soon.
>
> Based-on: <20250312152933.383967-7-gr...@kaod.org>
> Signed-off-by: Christian Schoenebeck <qemu_...@crudebyte.com>
> ---
> hw/9pfs/9p.c | 14 ++++++++------
> hw/9pfs/codir.c | 3 ++-
> hw/9pfs/cofile.c | 3 ++-
> 3 files changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> index b22df3aa2b..f4ca8e4db5 100644
> --- a/hw/9pfs/9p.c
> +++ b/hw/9pfs/9p.c
> @@ -434,7 +434,6 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu)
> V9fsFidState *f;
> GHashTableIter iter;
> gpointer fid;
> - int err;
> int nclosed = 0;
>
> /* prevent multiple coroutines running this function simultaniously */
> @@ -507,13 +506,16 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu)
> */
> v9fs_co_run_in_worker({
> QSLIST_FOREACH(f, &reclaim_list, reclaim_next) {
> - err = (f->fid_type == P9_FID_DIR) ?
> + /*
> + * 'man 2 close' suggests to ignore close() errors except of
> EBADF,
> + * not checking for EBADF here either as FIDs were picked above
> by
> + * having a valid file descriptor
> + */
> + (f->fid_type == P9_FID_DIR) ?
> s->ops->closedir(&s->ctx, &f->fs_reclaim) :
> s->ops->close(&s->ctx, &f->fs_reclaim);
> - if (!err) {
> - /* total_open_fd must only be mutated on main thread */
> - nclosed++;
> - }
> + /* total_open_fd must only be mutated on main thread */
> + nclosed++;
> }
> });
> total_open_fd -= nclosed;
> diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c
> index 2068a4779d..f1fd97c8a7 100644
> --- a/hw/9pfs/codir.c
> +++ b/hw/9pfs/codir.c
> @@ -353,7 +353,8 @@ int coroutine_fn v9fs_co_closedir(V9fsPDU *pdu,
> V9fsFidOpenState *fs)
> err = -errno;
> }
> });
> - if (!err) {
> + /* 'man 2 close' suggests to ignore close() errors except of EBADF */
> + if (!err || errno != EBADF) {
> total_open_fd--;
> }
> return err;
Or, as EBADF is somewhat unexpected here (assuming v9fs_co_closedir() was
called by checking for a valid file handle), maybe it would make sense to log
this?
if (unlikely(err && errno == EBADF)) {
error_report("v9fs_co_closedir() failed with EBADF");
} else {
total_open_fd--;
}
In the sense, if EBADF happens here, it's an indication for a bug in 9p
server.
> diff --git a/hw/9pfs/cofile.c b/hw/9pfs/cofile.c
> index 71174c3e4a..1e9f6da42a 100644
> --- a/hw/9pfs/cofile.c
> +++ b/hw/9pfs/cofile.c
> @@ -197,7 +197,8 @@ int coroutine_fn v9fs_co_close(V9fsPDU *pdu,
> V9fsFidOpenState *fs)
> err = -errno;
> }
> });
> - if (!err) {
> + /* 'man 2 close' suggests to ignore close() errors except of EBADF */
> + if (!err || errno != EBADF) {
> total_open_fd--;
> }
> return err;
Same here then.
/Christian
