Re: [Qemu-devel] [PATCH v3 06/46] ivshmem: remove unnecessary dup()

["Marc-André Lureau" <mlureau@redhat.com>]

Hi

----- Original Message -----
> On 15.09.2015 18:07, marcandre.lureau@redhat.com wrote:
> > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > 
> > qemu_chr_fe_get_msgfd() transfers ownership, there is no need to dup the
> > fd.
> > 
> 
> Are you sure? (tested?)
> There is a specific comment that the dup is done because of the get_msgfds
> implementation,
> I checked tcp_get_msgfds and it closes unused fds, is this ok?
> 
> static int tcp_get_msgfds(...)
> {
> ...
> /* Close unused fds */
> for (i = to_copy, i < s->read_msgfds_num; i++) {
>     close(s->read_msgfds[i]);
> }
> ...

Yes, it closes the remaining fds. But for the others, the one it got, there is no need for an extra dup() since the ownership is transfered.

> 
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ---
> >  hw/misc/ivshmem.c | 21 ++++++---------------
> >  1 file changed, 6 insertions(+), 15 deletions(-)
> > 
> > diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> > index dd15f0e..fbeb731 100644
> > --- a/hw/misc/ivshmem.c
> > +++ b/hw/misc/ivshmem.c
> > @@ -480,7 +480,7 @@ static bool fifo_update_and_get(IVShmemState *s, const
> > uint8_t *buf, int size,
> >  static void ivshmem_read(void *opaque, const uint8_t *buf, int size)
> >  {
> >      IVShmemState *s = opaque;
> > -    int incoming_fd, tmp_fd;
> > +    int incoming_fd;
> >      int guest_max_eventfd;
> >      long incoming_posn;
> >  
> > @@ -495,21 +495,21 @@ static void ivshmem_read(void *opaque, const uint8_t
> > *buf, int size)
> >      }
> >  
> >      /* pick off s->server_chr->msgfd and store it, posn should accompany
> >      msg */
> > -    tmp_fd = qemu_chr_fe_get_msgfd(s->server_chr);
> > -    IVSHMEM_DPRINTF("posn is %ld, fd is %d\n", incoming_posn, tmp_fd);
> > +    incoming_fd = qemu_chr_fe_get_msgfd(s->server_chr);
> > +    IVSHMEM_DPRINTF("posn is %ld, fd is %d\n", incoming_posn,
> > incoming_fd);
> >  
> >      /* make sure we have enough space for this guest */
> >      if (incoming_posn >= s->nb_peers) {
> >          if (increase_dynamic_storage(s, incoming_posn) < 0) {
> >              error_report("increase_dynamic_storage() failed");
> > -            if (tmp_fd != -1) {
> > -                close(tmp_fd);
> > +            if (incoming_fd != -1) {
> > +                close(incoming_fd);
> >              }
> >              return;
> >          }
> >      }
> >  
> > -    if (tmp_fd == -1) {
> > +    if (incoming_fd == -1) {
> >          /* if posn is positive and unseen before then this is our posn*/
> >          if ((incoming_posn >= 0) &&
> >                              (s->peers[incoming_posn].eventfds == NULL)) {
> > @@ -524,15 +524,6 @@ static void ivshmem_read(void *opaque, const uint8_t
> > *buf, int size)
> >          }
> >      }
> >  
> > -    /* because of the implementation of get_msgfd, we need a dup */
> > -    incoming_fd = dup(tmp_fd);
> > -
> > -    if (incoming_fd == -1) {
> > -        error_report("could not allocate file descriptor %s",
> > strerror(errno));
> > -        close(tmp_fd);
> > -        return;
> > -    }
> > -
> >      /* if the position is -1, then it's shared memory region fd */
> >      if (incoming_posn == -1) {
> >  
> > 
> 
>