[libvirt] [PATCH 2/3] qemu: support passing pre-opened UNIX socket listen FD

Ján Tomko jtomko at redhat.com
Mon Mar 26 13:19:36 UTC 2018


On Wed, Mar 14, 2018 at 05:33:05PM +0000, Daniel P. Berrangé wrote:
>There is a race condition when spawning QEMU where libvirt has spawned
>QEMU but the monitor socket is not yet open. Libvirt has to repeatedly
>try to connect() to QEMU's monitor until eventually it succeeds, or
>times out. We use kill() to check if QEMU is still alive so we avoid
>waiting a long time if QEMU exited, but having a timeout at all is still
>unpleasant.
>
>With QEMU 2.12 we can pass in a pre-opened FD for UNIX domain or TCP
>sockets. If libvirt has called bind() and listen() on this FD, then we
>have a guarantee that libvirt can immediately call connect() and
>succeed without any race.
>
>Although we only really care about this for the monitor socket and agent
>socket, this patch does FD passing for all UNIX socket based character
>devices since there appears to be no downside to it.
>
>We don't do FD passing for TCP sockets, however, because it is only
>possible to pass a single FD, while some hostnames may require listening
>on multiple FDs to cover IPv4 and IPv6 concurrently.
>
>Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
>---
> src/qemu/qemu_command.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 56 insertions(+), 2 deletions(-)
>
>diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
>index fa0aa5d5c3..291aad13cf 100644
>--- a/src/qemu/qemu_command.c
>+++ b/src/qemu/qemu_command.c
>@@ -5010,8 +5010,62 @@ qemuBuildChrChardevStr(virLogManagerPtr logManager,
>         break;
>
>     case VIR_DOMAIN_CHR_TYPE_UNIX:
>-        virBufferAsprintf(&buf, "socket,id=%s,path=", charAlias);
>-        virQEMUBuildBufferEscapeComma(&buf, dev->data.nix.path);
>+#ifndef WIN32

Why the ifdef?

Do we even build QEMU driver on WIN32?

Jan
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: Digital signature
URL: <http://listman.redhat.com/archives/libvir-list/attachments/20180326/85e923b9/attachment-0001.sig>


More information about the libvir-list mailing list