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



On 04/18/2013 12:43 PM, Daniel P. Berrange wrote:
> 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 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.
> 

I completely missed the fact that this could be used for something else
than libvirtd, thanks for pointing that out.  Could you point me to the
place where we use the approach you described?

Thanks,
Martin


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