9pfs: fix FD leak and reduce latency of v9fs_reclaim_fd()

9pfs: fix FD leak and reduce latency of v9fs_reclaim_fd()

This patch fixes two different bugs in v9fs_reclaim_fd():

1. Reduce latency:

This function calls v9fs_co_close() and v9fs_co_closedir() in a loop. Each
one of the calls adds two thread hops (between main thread and a fs driver
background thread). Each thread hop adds latency, which sums up in
function's loop to a significant duration.

Reduce overall latency by open coding what v9fs_co_close() and
v9fs_co_closedir() do, executing those and the loop itself altogether in
only one background thread block, hence reducing the total amount of
thread hops to only two.

2. Fix file descriptor leak:

The existing code called v9fs_co_close() and v9fs_co_closedir() to close
file descriptors. Both functions check right at the beginning if the 9p
request was cancelled:

    if (v9fs_request_cancelled(pdu)) {
        return -EINTR;
    }

So if client sent a 'Tflush' message, v9fs_co_close() / v9fs_co_closedir()
returned without having closed the file descriptor and v9fs_reclaim_fd()
subsequently freed the FID without its file descriptor being closed, hence
leaking those file descriptors.

This 2nd bug is fixed by this patch as well by open coding v9fs_co_close()
and v9fs_co_closedir() inside of v9fs_reclaim_fd() and not performing the
v9fs_request_cancelled(pdu) check there.

Fixes: 7a46274529c ('hw/9pfs: Add file descriptor reclaim support')
Fixes: bccacf6c792 ('hw/9pfs: Implement TFLUSH operation')
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <5747469d3f039c53147e850b456943a1d4b5485c.1741339452.git.qemu_oss@crudebyte.com>