[libvirt] [PATCH 3/3] Speed up waiting for the session daemon

[Daniel P. Berrange]

On Thu, Apr 18, 2013 at 12:30:56PM +0200, Martin Kletzander wrote:
> Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=927369
> 
> When launching the session daemon, we were waiting for around 20
> seconds even it died before creating any sockets etc.
> 
> The following modification pre-creates the pidfile which will be used
> by the forked daemon and cleans it up in case the daemon doesn't start
> successfully.  This makes it possible to check whether the daemon
> started and died immediately.
> 
> The pidfile is needed due to the process being daemonized.  Neither
> creation nor locking the pidfile will fail in the daemon thanks to the
> same PID keeping the lock.
> 
> Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
> ---
>  src/rpc/virnetsocket.c | 41 +++++++++++++++++++++++++++++++++++------
>  1 file changed, 35 insertions(+), 6 deletions(-)
> 
> diff --git a/src/rpc/virnetsocket.c b/src/rpc/virnetsocket.c
> index c4fd9ee..835e11f 100644
> --- a/src/rpc/virnetsocket.c
> +++ b/src/rpc/virnetsocket.c
> @@ -52,6 +52,7 @@
>  #include "virfile.h"
>  #include "virthread.h"
>  #include "virprocess.h"
> +#include "virpidfile.h"
> 
>  #include "passfd.h"
> 
> @@ -119,20 +120,29 @@ VIR_ONCE_GLOBAL_INIT(virNetSocket)
> 
> 
>  #ifndef WIN32
> -static int virNetSocketForkDaemon(const char *binary)
> +static int virNetSocketForkDaemon(const char *binary, char **pidfile)
>  {
> -    int ret;
> +    int ret = -1;
>      virCommandPtr cmd = virCommandNewArgList(binary,
>                                               "--timeout=30",
>                                               NULL);
> 
> +    if (pidfile &&
> +        virGetDaemonPidFilePath(false, pidfile) < 0) {
> +        goto cleanup;
> +    }

And here, you're hardcoding use of the libvirtd pid file in a
method that is used to spawn any type of daemon.

The much better way to deal with this is to follow the approach that
systemd uses for race-free activation of daemons. Namely pass in the
pre-opened listen socket to the daemon. We already support this for
the virtlockd daemon and it would be easy to support it for libvirtd
too. This leaves the daemons in charge of their own pidfiles.

Regards,
Daniel
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