On Thu, Jan 17, 2013 at 08:55:14AM +0100, Michal Privoznik wrote:
> Currently, whenever somebody calls saferead() on nonblocking FD
> (safewrite() is totally interchangeable for purpose of this message)
> he might get wrong return value. For instance, in the first iteration
> some data is read. The number of bytes read is stored into local
> variable 'nread'. However, in next iterations we can get -1 from
> read() with errno == EAGAIN, in which case the -1 is returned despite
> fact some data has already been read. So the caller gets confused.
> Bare read() should be used for nonblocking FD.
> ---
> src/util/virutil.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/src/util/virutil.c b/src/util/virutil.c
> index b36e9d3..bc970a4 100644
> --- a/src/util/virutil.c
> +++ b/src/util/virutil.c
> @@ -98,7 +98,9 @@ verify(sizeof(gid_t) <= sizeof(unsigned int) &&
>
> #define VIR_FROM_THIS VIR_FROM_NONE
>
> -/* Like read(), but restarts after EINTR */
> +/* Like read(), but restarts after EINTR.
> + * Doesn't play nicely with nonblocking FD and EAGAIN,
> + * in which case you want to use bare read() */
> ssize_t
> saferead(int fd, void *buf, size_t count)
> {
> @@ -118,7 +120,9 @@ saferead(int fd, void *buf, size_t count)
> return nread;
> }
>
> -/* Like write(), but restarts after EINTR */
> +/* Like write(), but restarts after EINTR.
> + * Doesn't play nicely with nonblocking FD and EAGAIN,
> + * in which case you want to use bare write() */
> ssize_t
> safewrite(int fd, const void *buf, size_t count)
> {
ACK
Or even use virSocket() if the FD is related to a socket rather than a
plain file or pipe.
Daniel
--
|: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :|
|: http://libvirt.org -o- http://virt-manager.org :|
|: http://autobuild.org -o- http://search.cpan.org/~danberr/ :|
|: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
--
libvir-list mailing list
libvir-list@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/libvir-list