Re: [libvirt] [Qemu-devel] [PATCH v7 6/6] block: Enable qemu_open/close to work with fd sets
On 08/08/2012 09:02 AM, Stefan Hajnoczi wrote:
On Tue, Aug 07, 2012 at 11:58:28AM -0400, Corey Bryant wrote:
> @@ -2566,6 +2567,92 @@ FdsetInfoList *qmp_query_fdsets(Error **errp)
> return fdset_list;
> }
>
> +int monitor_fdset_get_fd(int64_t fdset_id, int flags)
> +{
> + mon_fdset_t *mon_fdset;
> + mon_fdset_fd_t *mon_fdset_fd;
> + int mon_fd_flags;
> +
> + QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
> + if (mon_fdset->id != fdset_id) {
> + continue;
> + }
> + QLIST_FOREACH(mon_fdset_fd, &mon_fdset->fds, next) {
> + if (mon_fdset_fd->removed) {
> + continue;
> + }
This makes me wonder about immediately closing in remove-fd and drop the
removed field. This way, code using mon_fdset->fds does not need to
worry about removed=true fds.
The reason we don't immediately close in remove-fd is so that the client
doesn't have to keep track of what fd's are in use by QEMU.
Let's say libvirt uses add-fd to add fd=4 (O_RDONLY) and fd=5 (O_RDWR)
to fd set 2 and they both refer to /mnt/nfs/data.img. libvirt can then
issue a command that uses the fd (e.g. drive_add file=/dev/fdsets/2).
QEMU then opens and closes that file as it desires by dup'ing the fd in
the fd set that has matching access mode (O_RDONLY or O_RDWR) and
closing the dup'd fd.
By not closing the fd immediately in remove-fd, we allow the client to
issue a command like drive_open and immediately follow it with a
remove-fd and not have to worry about determining when QEMU is done
using the fd.
--
Regards,
Corey