Re: [PATCH] sockets: update SOCKET_ADDRESS_TYPE_FD listen(2) backlog

[Stefan Hajnoczi]

On Tue, Mar 16, 2021 at 08:35:14AM -0500, Eric Blake wrote:
> On 3/16/21 4:10 AM, Stefan Hajnoczi wrote:
> > On Wed, Mar 10, 2021 at 05:30:04PM +0000, Stefan Hajnoczi wrote:
> >> socket_get_fd() fails with the error "socket_get_fd: too many
> >> connections" if the given listen backlog value is not 1.
> >>
> >> Not all callers set the backlog to 1. For example, commit
> >> 582d4210eb2f2ab5baac328fe4b479cd86da1647 ("qemu-nbd: Use SOMAXCONN for
> >> socket listen() backlog") uses SOMAXCONN. This will always fail with in
> >> socket_get_fd().
> >>
> >> This patch calls listen(2) on the fd to update the backlog value. The
> >> socket may already be in the listen state. I have tested that this works
> >> on Linux 5.10 and macOS Catalina.
> >>
> >> As a bonus this allows us to detect when the fd cannot listen. Now we'll
> >> be able to catch unbound or connected fds in socket_listen().
> >>
> >> Drop the num argument from socket_get_fd() since this function is also
> >> called by socket_connect() where a listen backlog value does not make
> >> sense.
> >>
> >> Fixes: e5b6353cf25c99c3f08bf51e29933352f7140e8f ("socket: Add backlog 
> >> parameter to socket_listen")
> >> Reported-by: Richard W.M. Jones <rjones@redhat.com>
> >> Cc: Juan Quintela <quintela@redhat.com>
> >> Cc: Eric Blake <eblake@redhat.com>
> >> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> >> ---
> >>  util/qemu-sockets.c | 29 ++++++++++++++++++++++-------
> >>  1 file changed, 22 insertions(+), 7 deletions(-)
> > 
> > Dan and Gerd: Can this go via one of your trees?
> > 
> 
> As it showed up as a regression in qemu-nbd, I can also consider queuing
> it in my NBD tree.  However, I claim it counts as a bug fix, so it is
> fine for -rc1 even if it misses soft freeze.
> 
> I'm fine whichever maintainer takes this, although I've now flagged it
> to go through an NBD pull request if it doesn't land elsewhere sooner.

Hi Eric,
Is this patch going into QEMU 6.0?

Thanks,
Stefan

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