[libvirt] [PATCH v4 10/14] qemu: Start PR daemon on domain startup

[Michal Privoznik]

On 04/14/2018 04:56 PM, John Ferlan wrote:
> 
> 
> On 04/10/2018 10:58 AM, Michal Privoznik wrote:
>> Before we exec() qemu we have to spawn pr-helper processes for
>> all managed reservations (well, technically there can only one).
> 
> Don't mince words - what have to spawn the qemu-pr-helper process for
> all managed persistent reservations.
> 
>> The only caveat there is that we should place the process into
>> the same namespace and cgroup as qemu (so that it shares the same
>> view of the system). But we can do that only after we've forked.
>> That means calling the setup function between fork() and exec().
>>
>> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>> ---
>>  src/qemu/qemu_process.c | 224 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 224 insertions(+)
>>
>> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
>> index f02114c693..982c989a0a 100644
>> --- a/src/qemu/qemu_process.c
>> +++ b/src/qemu/qemu_process.c
>> @@ -2556,6 +2556,223 @@ qemuProcessResctrlCreate(virQEMUDriverPtr driver,
>>      ret = 0;
>>   cleanup:
>>      virObjectUnref(caps);
>> +
>> +    return ret;
>> +}
>> +
>> +
>> +static char *
>> +qemuProcessBuildPRHelperPidfilePath(virDomainObjPtr vm,
>> +                                    const char *prdAlias)
>> +{
>> +    qemuDomainObjPrivatePtr priv = vm->privateData;
>> +
>> +    return virPidFileBuildPath(priv->libDir, prdAlias);
>> +}
>> +
>> +
>> +static void
>> +qemuProcessKillPRDaemon(virDomainObjPtr vm)
>> +{
>> +    virErrorPtr orig_err;
>> +    char *prAlias;
>> +    char *prPidfile;
> 
> I would hope that we'd be able to figure out in some way that we
> actually started this for the the domain.
> 
>> +
>> +    if (!(prAlias = qemuDomainGetManagedPRAlias())) {
>> +        VIR_WARN("Unable to get default PR manager alias");
>> +        return;
>> +    }
>> +
>> +    if (!(prPidfile = qemuProcessBuildPRHelperPidfilePath(vm, prAlias))) {
> 
> Since we know that we're using the managed one, then we should be able
> to pass/formulate the "static" prAlias here rather than possibly failing
> because we don't have enough memory above and then need to free it
> immediately afterwards.

Yeah, well if there's not enough memory to allocate 11 bytes there's
probably not enough memory to do any stuff done below, i.e.
qemuProcessBuildPRHelperPidfilePath(), or any syscall done in
virPidFileForceCleanupPath().

> 
>> +        VIR_WARN("Unable to construct pr-helper pidfile path");
>> +        VIR_FREE(prAlias);
>> +        return;
>> +    }
>> +    VIR_FREE(prAlias);
>> +
>> +    virErrorPreserveLast(&orig_err);
>> +    if (virPidFileForceCleanupPath(prPidfile) < 0) {
>> +        VIR_WARN("Unable to kill pr-helper process");
>> +    } else if (unlink(prPidfile) < 0 &&
>> +               errno != ENOENT) {
>> +        virReportSystemError(errno,
>> +                             _("Unable to remove stale pidfile %s"),
>> +                             prPidfile);
>> +    }
>> +    virErrorRestore(&orig_err);
>> +
>> +    VIR_FREE(prPidfile);
>> +}
>> +

>> +static int
>> +qemuProcessMaybeStartPRDaemon(virDomainObjPtr vm)
>> +{
>> +    size_t i;
>> +    int ret = -1;
>> +    qemuDomainDiskPRDPtr prd = NULL;
>> +
>> +    for (i = 0; i < vm->def->ndisks; i++) {
>> +        const virDomainDiskDef *disk = vm->def->disks[i];
>> +        qemuDomainStorageSourcePrivatePtr srcPriv;
>> +
>> +        if (!virStoragePRDefIsManaged(disk->src->pr))
>> +            continue;
>> +
>> +        srcPriv = QEMU_DOMAIN_STORAGE_SOURCE_PRIVATE(disk->src);
>> +        prd = srcPriv->prd;
>> +        break;
>> +    }
> 
> Now that we know we needed to start one, then once we're successful we
> should be able to store that we did start it... and that could be added
> to some sort of private structure.  This is where I could see a private
> data being used.

Well, we can have that when qemu finally implements events. Then we can
keep this internal state in sync with reality.

Michal