[PATCH] qemu: clear residual QMP caps processes during QEMU driver initialization

[Daniel Henrique Barboza]

On 7/17/20 8:10 AM, Bihong Yu wrote:
>>From c328ff62b11d58553fd2032a85fd3295e009b3d3 Mon Sep 17 00:00:00 2001
> From: Bihong Yu <yubihong at huawei.com>
> Date: Fri, 17 Jul 2020 16:55:12 +0800
> Subject: [PATCH] qemu: clear residual QMP caps processes during QEMU driver
>   initialization
> 
> In some cases, the QMP capabilities processes possible residue. So we need to
> clear the residual QMP caps processes during starting libvirt.

Which cases are you referring to? Do you have a reproducer for this behavior? I
tried it up starting and stopping libvirtd, fetching capabilities, starting vms
and so on, and wasn't able to see any 'qmp.pid' file hanging around.

About the code, I looked it up and all calls to qemuProcessQMPNew() are being
cleaned up accordingly with a qemuProcessQMPFree() function, which calls
qemuProcessQMPStop(), and the Stop function cleans up both the pid file and
the uniqDir:

----- qemuProcessQMPStop(qemuProcessQMPPtr proc) -----

     if (proc->pidfile)
         unlink(proc->pidfile);

     if (proc->uniqDir)
         rmdir(proc->uniqDir);

------

The proper fix here would be to understand in which conditions the 'qmp.pid' file
is being left behind and make the code go through the existing cleanup path,
fixing qemuProcessQMPFree and/or qemuProcessQMPStop if needed. What you're doing
here works, but it's fixing the symptom of a bug instead of the bug itself.


Thanks,


DHB


> 
> Signed-off-by:Bihong Yu <yubihong at huawei.com>
> ---
>   src/qemu/qemu_driver.c  |  2 ++
>   src/qemu/qemu_process.c | 40 ++++++++++++++++++++++++++++++++++++++++
>   src/qemu/qemu_process.h |  2 ++
>   3 files changed, 44 insertions(+)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index d185666..d627fd7 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -889,6 +889,8 @@ qemuStateInitialize(bool privileged,
>           run_gid = cfg->group;
>       }
> 
> +    qemuProcessQMPClear(cfg->libDir);
> +
>       qemu_driver->qemuCapsCache = virQEMUCapsCacheNew(cfg->libDir,
>                                                        cfg->cacheDir,
>                                                        run_uid,
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index 70fc24b..d545e3e 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -8312,6 +8312,46 @@ static qemuMonitorCallbacks callbacks = {
>   };
> 
> 
> +/**
> + * qemuProcessQMPClear
> + *
> + * Try to kill residual QMP caps processes
> + */
> +void
> +qemuProcessQMPClear(const char *libDir)
> +{
> +    virErrorPtr orig_err;
> +    DIR *dirp = NULL;
> +    struct dirent *dp;
> +
> +    if (!virFileExists(libDir))
> +        return;
> +
> +    if (virDirOpen(&dirp, libDir) < 0)
> +        return;
> +
> +    virErrorPreserveLast(&orig_err);
> +    while (virDirRead(dirp, &dp, libDir) > 0) {
> +        g_autofree char *qmp_uniqDir = NULL;
> +        g_autofree char *qmp_pidfile = NULL;
> +
> +        if (!STRPREFIX(dp->d_name, "qmp-"))
> +            continue;
> +
> +        qmp_uniqDir = g_strdup_printf("%s/%s", libDir, dp->d_name);
> +        qmp_pidfile = g_strdup_printf("%s/%s", qmp_uniqDir, "qmp.pid");
> +
> +        ignore_value(virPidFileForceCleanupPath(qmp_pidfile));
> +
> +        if (qmp_uniqDir)
> +            rmdir(qmp_uniqDir);
> +    }
> +    virErrorRestore(&orig_err);
> +
> +    VIR_DIR_CLOSE(dirp);
> +}
> +
> +
>   static void
>   qemuProcessQMPStop(qemuProcessQMPPtr proc)
>   {
> diff --git a/src/qemu/qemu_process.h b/src/qemu/qemu_process.h
> index 15e67b9..b039e6c 100644
> --- a/src/qemu/qemu_process.h
> +++ b/src/qemu/qemu_process.h
> @@ -233,6 +233,8 @@ qemuProcessQMPPtr qemuProcessQMPNew(const char *binary,
>                                       gid_t runGid,
>                                       bool forceTCG);
> 
> +void qemuProcessQMPClear(const char *libDir);
> +
>   void qemuProcessQMPFree(qemuProcessQMPPtr proc);
> 
>   int qemuProcessQMPStart(qemuProcessQMPPtr proc);
>