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Re: [PATCH v2] qemu-nbd: Use SOMAXCONN for socket listen() backlog
From: |
Eric Blake |
Subject: |
Re: [PATCH v2] qemu-nbd: Use SOMAXCONN for socket listen() backlog |
Date: |
Mon, 8 Feb 2021 10:45:22 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 |
On 2/8/21 4:00 AM, Daniel P. Berrangé wrote:
> On Fri, Feb 05, 2021 at 12:57:05PM -0600, Eric Blake wrote:
>> Our default of a backlog of 1 connection is rather puny, particularly
>> for scenarios where we expect multiple listeners to connect (such as
>> qemu-nbd -e X). This is especially important for Unix sockets, as a
>> definite benefit to clients: at least on Linux, a client trying to
>> connect to a Unix socket with a backlog gets an EAGAIN failure with no
>> way to poll() for when the backlog is no longer present short of
>> sleeping an arbitrary amount of time before retrying.
>>
>> See https://bugzilla.redhat.com/1925045 for a demonstration of where
>> our low backlog prevents libnbd from connecting as many parallel
>> clients as it wants.
>>
>> Reported-by: Richard W.M. Jones <rjones@redhat.com>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
>> ---
>>
>> v2: target the correct API used by qemu-nbd, rather than an unrelated
>> legacy wrapper [Dan]
>>
>> qemu-nbd.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/qemu-nbd.c b/qemu-nbd.c
>> index 608c63e82a25..cd20ee73be19 100644
>> --- a/qemu-nbd.c
>> +++ b/qemu-nbd.c
>> @@ -965,7 +965,8 @@ int main(int argc, char **argv)
>> server = qio_net_listener_new();
>> if (socket_activation == 0) {
>> saddr = nbd_build_socket_address(sockpath, bindto, port);
>> - if (qio_net_listener_open_sync(server, saddr, 1, &local_err) < 0) {
>> + if (qio_net_listener_open_sync(server, saddr, SOMAXCONN,
>> + &local_err) < 0) {
>
> This addresses qemu-nbd, but surely we want to be consistent with the
> QMP nbd-server-start impl too, in blockdev-nbd.c
>
Good point, I'll send v3.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org