[libvirt] [PATCH 04/10] qemu: agent: handle agent connection errors in one place
Nikolay Shirokovskiy
nshirokovskiy at virtuozzo.com
Fri Oct 28 07:37:13 UTC 2016
On 27.10.2016 18:51, John Ferlan wrote:
>
>
> On 10/27/2016 07:34 AM, Nikolay Shirokovskiy wrote:
>>
>>
>> On 26.10.2016 22:57, John Ferlan wrote:
>>>
>>> There's no commit message...
>>
>> This is simple refactoring.
>>
>
> Not really...
>
> A simple refactor would have kept the -2 logic.
Ohh, my bad english. I mean just(mere) refactoring. Not simple.
However as a refactoring step this patch is not complex from my POV.
>
> What's been done here is to let qemuConnectAgent make the decision on
> "hard" or "soft" error and only use < 0 as failure
>
>>>
>>> You're altering qemuConnectAgent to return -1 on the only error and
>>> perform the VIR_WARN plus agentError = true on other "soft" failures.
>>>
>>> Not exactly nothing going on!
>>
>> This is what already present in code, I've just moved soft failures
>> in qemuConnectAgent.
>>
>>>
>>> On 10/04/2016 02:56 AM, Nikolay Shirokovskiy wrote:
>>>> ---
>>>> src/qemu/qemu_driver.c | 8 +------
>>>> src/qemu/qemu_migration.c | 13 ++---------
>>>> src/qemu/qemu_process.c | 58 ++++++++++++-----------------------------------
>>>> 3 files changed, 17 insertions(+), 62 deletions(-)
>>>>
>>>
>>> This idea seems to have merit too - something that I've thought now that
>>> I've read the first 3 patches...
>>>
>>> I think you should have started with this patch, it probably would have
>>> made the others easier to think about. In fact, I'm curious if with just
>>> this change and the suggestion in patch 3 for clearing agentError
>>> whether you can reproduced the bug you're trying to fix/resolve without
>>> any of the other patches.
>>>
>>>> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
>>>> index 12ddbc0..edff973 100644
>>>> --- a/src/qemu/qemu_driver.c
>>>> +++ b/src/qemu/qemu_driver.c
>>>> @@ -4397,7 +4397,6 @@ processSerialChangedEvent(virQEMUDriverPtr driver,
>>>> virObjectEventPtr event = NULL;
>>>> virDomainDeviceDef dev;
>>>> qemuDomainObjPrivatePtr priv = vm->privateData;
>>>> - int rc;
>>>>
>>>> if (connected)
>>>> newstate = VIR_DOMAIN_CHR_DEVICE_STATE_CONNECTED;
>>>> @@ -4450,13 +4449,8 @@ processSerialChangedEvent(virQEMUDriverPtr driver,
>>>>
>>>> if (STREQ_NULLABLE(dev.data.chr->target.name, "org.qemu.guest_agent.0")) {
>>>> if (newstate == VIR_DOMAIN_CHR_DEVICE_STATE_CONNECTED) {
>>>> - if (!priv->agent) {
>>>> - if ((rc = qemuConnectAgent(driver, vm)) == -2)
>>>> + if (!priv->agent && qemuConnectAgent(driver, vm) < 0)
>>>
>>> FWIW:
>>> qemuConnectAgent returns 0 "if (priv->agent)", so there's one less check
>>> here too. Could just be "if (qemuConnectAgent(driver, vm) < 0)"
>>
>> It depends on patch 3. If we clear the error early in qemuConnectAgent then
>> we'd better check before calling this function.
>>
>
> Right my mind was already there or more succinctly said - I was trying
> to consider this as the first patch as I think it'll make the reasoning
> a bit more clear.
Agree.
>
> Since the "issue" has been described now as a pure shutdown and restart
> after error problem without needing to consider the migration,
> reconnect, and attach separately - it's easier to focus on.
>
> So my feeling now after reading and thinking a bit about everything so
> far is that this patch could go in (mostly) as is. That way there are
> then 2 places to set agentError=true and two places to set
> agentError=false (discluding original allocation and reconnect paths).
>
> I don't think we can "combine" the Error and EOF paths. They're
> separate. What happens if some day someone uses the VSERPORT logic to
Right now there is no value in separation AFAIU but a lot of code that is
difficult to follow.
> somehow restart an agent after an error, after a close, and before a
> shutdown. IOW: Some kind of error recovery logic.
Dont's see how having separate EOF and Error will help in this case.
>
> In order to handle the issue where agentError is set, but we cannot
> start again (e.g. the have error, do shutdown, do start path) - add an
> unconditional priv->agentError = false before in qemuConnectAgent before
> the virSecurityManagerSetDaemonSocketLabel call. The other agentError =
> false settings can then be removed.
Can not agree. For modern qemu agent will be in error state on start up
until serial port appeared. Should be in 'not connected' state.
>
> So we're left with 2 places to set error and one place to clear. I'll
> continue to consider this, bug figured I'd get out a response to all
> this sooner than later.
>
> I'm less convinced mucking with combining EOF and Error is a good idea
> in patches 7-10, but I haven't thought too much about it either.
>
> John
>>>
>>>> goto endjob;
>>>
>>> The indention for this is off (remove leading 4 spaces)
>>>
>>>> -
>>>> - if (rc < 0)
>>>> - priv->agentError = true;
>>>> - }
>>>> } else {
>>>> if (priv->agent) {
>>>> qemuAgentClose(priv->agent);
>>>> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
>>>> index e2ca330..0a02236 100644
>>>> --- a/src/qemu/qemu_migration.c
>>>> +++ b/src/qemu/qemu_migration.c
>>>> @@ -6171,7 +6171,6 @@ qemuMigrationFinish(virQEMUDriverPtr driver,
>>>> unsigned short port;
>>>> unsigned long long timeReceived = 0;
>>>> virObjectEventPtr event;
>>>> - int rc;
>>>> qemuDomainJobInfoPtr jobInfo = NULL;
>>>> bool inPostCopy = false;
>>>> bool doKill = true;
>>>> @@ -6244,16 +6243,8 @@ qemuMigrationFinish(virQEMUDriverPtr driver,
>>>> QEMU_ASYNC_JOB_MIGRATION_IN) < 0)
>>>> goto endjob;
>>>>
>>>> - if ((rc = qemuConnectAgent(driver, vm)) < 0) {
>>>> - if (rc == -2)
>>>> - goto endjob;
>>>> -
>>>> - VIR_WARN("Cannot connect to QEMU guest agent for %s",
>>>> - vm->def->name);
>>>> - virResetLastError();
>>>> - priv->agentError = true;
>>>> - }
>>>> -
>>>> + if (qemuConnectAgent(driver, vm) < 0)
>>>> + goto endjob;
>>>>
>>>> if (flags & VIR_MIGRATE_PERSIST_DEST) {
>>>> if (qemuMigrationPersist(driver, vm, mig, !v3proto) < 0) {
>>>> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
>>>> index 42f7f84..d7c9ce3 100644
>>>> --- a/src/qemu/qemu_process.c
>>>> +++ b/src/qemu/qemu_process.c
>>>> @@ -206,7 +206,6 @@ int
>>>> qemuConnectAgent(virQEMUDriverPtr driver, virDomainObjPtr vm)
>>>> {
>>>> qemuDomainObjPrivatePtr priv = vm->privateData;
>>>> - int ret = -1;
>>>> qemuAgentPtr agent = NULL;
>>>> virDomainChrDefPtr config = qemuFindAgentConfig(vm->def);
>>>>
>>>> @@ -252,8 +251,7 @@ qemuConnectAgent(virQEMUDriverPtr driver, virDomainObjPtr vm)
>>>> qemuAgentClose(agent);
>>>> virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
>>>> _("guest crashed while connecting to the guest agent"));
>>>> - ret = -2;
>>>> - goto cleanup;
>>>> + return -1;
>>>> }
>>>>
>>>> if (virSecurityManagerClearSocketLabel(driver->securityManager,
>>>> @@ -264,18 +262,16 @@ qemuConnectAgent(virQEMUDriverPtr driver, virDomainObjPtr vm)
>>>> goto cleanup;
>>>> }
>>>>
>>>> -
>>>> priv->agent = agent;
>>>>
>>>> - if (priv->agent == NULL) {
>>>> - VIR_INFO("Failed to connect agent for %s", vm->def->name);
>>>
>>> Interesting a "marker" of sorts to know the virAgentOpen "failed" is
>>> that we'd get an Informational "Failed to connect..." followed shortly
>>> thereafter by a Warning "Cannot connect..." (depending of course on
>>> one's message display severity level).
>>>
>>> I think if you "restore" this without the goto cleanup (below) and of
>>> course the removal of the {}, then at least message parity is
>>> achieved... I suppose it could move up into the "if (agent == NULL)"
>>> too, but then it could be given even though an Error is reported.
>>>
>>> It's not that important, but it does leave some breadcrumbs.
>>
>> Agree. Even though I'm still wondering how useful this message is as
>> this patch is intended to be refactoring let's keep this message.
>>
>>>
>>> Again I'd like to see the breadcrumbs with just this patch applied to
>>> reproduced what you're chasing in patches 1-4...
>>>
>>
>> Sorry, not possible. The situation I've described in patch 1 is based on analysis. However
>> after applying the patches 1-3 the bug is not occured in our test system anymoree.
>>
>> Nikolay
>>
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