[PATCH v2] Add VM info to improve error log message for qemu monitor
Ani Sinha
ani at anisinha.ca
Tue Jan 4 10:00:00 UTC 2022
On Tue, 4 Jan 2022, Rohit Kumar wrote:
>
> On 03/01/22 7:12 pm, Ani Sinha wrote:
> >
> > On Wed, 22 Dec 2021, Rohit Kumar wrote:
> >
> > > This patch is to determine the VM which had IO or socket hangup error.
> > > Accessing directly vm->def->name inside qemuMonitorIO() or
> > > qemuMonitorSend()
> > > might leads to illegal access as we are out of 'vm' context and vm->def
> > > might
> > > not exist. Adding a field "domainName" inside mon object to access vm name
> > > and initialising it when creating mon object.
> > The commit message should desribe the purpose of the change, not how it is
> > done. That can be easily understood reading the code. As for why the
> > implementation follows a particular way, we can explain it in the code
> > comments.
> >
> > This change adds the domain name in the error and debug logs during
> > monitor IO processing so that we may infer which VM experienced those
> > errors etc. This may help in debugging monitor IO errors. IMHO this
> > decription is enough.
> Thanks Ani, I will update the commit message in the next patch.
> >
> > > Signed-off-by: Rohit Kumar <rohit.kumar3 at nutanix.com>
> > > ---
> > > diff to v1:
> > > - Adding a field domainName inside _qemuMonitor struct for accessing vm
> > > name
> > > instead of directly accessing mon->vm->def->name.
> > > - Link to v1:
> > > https://urldefense.proofpoint.com/v2/url?u=https-3A__listman.redhat.com_archives_libvir-2Dlist_2021-2DDecember_msg00217.html&d=DwIBAg&c=s883GpUCOChKOHiocYtGcg&r=ABSkr7gy7ZTfApFfI-Xxt1gZNtsDDiXoXOXc0OrkyFs&m=W2jEgk2s_xjLOLC-j8lPBnwVgteHS0-yYEGMqin16nmfzndzNgBE9mEvtbvyVzQo&s=Sa2q9edb4cvXo-EUriIPwlJxNo-itpp6--ZxY7rla2U&e=
> > > - Talked with peter on RFC and he suggested me to add a field inside
> > > monitor struct to get VM name.
> > >
> > > src/qemu/qemu_monitor.c | 47 +++++++++++++++++++++++++----------------
> > > 1 file changed, 29 insertions(+), 18 deletions(-)
> > >
> > > diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
> > > index dda6ae9796..c3a0227795 100644
> > > --- a/src/qemu/qemu_monitor.c
> > > +++ b/src/qemu/qemu_monitor.c
> > > @@ -80,6 +80,7 @@ struct _qemuMonitor {
> > > GSource *watch;
> > >
> > > virDomainObj *vm;
> > > + char *domainName;
> > >
> > Here we can explain why we are adding an extra member as opposed to
> > referencing it directly.
> Right, we can access it directly.
> >
> > > qemuMonitorCallbacks *cb;
> > > void *callbackOpaque;
> > > @@ -243,6 +244,7 @@ qemuMonitorDispose(void *obj)
> > > virCondDestroy(&mon->notify);
> > > g_free(mon->buffer);
> > > g_free(mon->balloonpath);
> > > + g_free(mon->domainName);
> > > }
> > >
> > >
> > > @@ -530,13 +532,18 @@ qemuMonitorIO(GSocket *socket G_GNUC_UNUSED,
> > > qemuMonitor *mon = opaque;
> > > bool error = false;
> > > bool hangup = false;
> > > + virDomainObj *vm = NULL;
> > > + char *vmName = NULL;
> > >
> > These initializations are redundant since ...
> Acknowledged.
> > > virObjectRef(mon);
> > >
> > > + vm = mon->vm;
> > > + vmName = mon->domainName;
> > you initialize them here anyway.
> I will remove these in next patch.
> >
> > > +
> > > /* lock access to the monitor and protect fd */
> > > virObjectLock(mon);
> > > #if DEBUG_IO
> > > - VIR_DEBUG("Monitor %p I/O on socket %p cond %d", mon, socket, cond);
> > > + VIR_DEBUG("Monitor %p I/O on socket %p cond %d vm=%p name=%s", mon,
> > > socket, cond, vm, NULLSTR(vmName));
> > > #endif
> > > if (mon->fd == -1 || !mon->watch) {
> > > virObjectUnlock(mon);
> > > @@ -583,8 +590,8 @@ qemuMonitorIO(GSocket *socket G_GNUC_UNUSED,
> > >
> > > if (!error && !mon->goteof &&
> > > cond & G_IO_ERR) {
> > > - virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> > > - _("Invalid file descriptor while waiting for
> > > monitor"));
> > > + virReportError(VIR_ERR_INTERNAL_ERROR,
> > > + _("%s: Invalid file descriptor while waiting
> > > for monitor"), NULLSTR(vmName));
> > As per
> > https://urldefense.proofpoint.com/v2/url?u=https-3A__libvirt.org_coding-2Dstyle.html-23error-2Dmessage-2Dformat&d=DwIBAg&c=s883GpUCOChKOHiocYtGcg&r=ABSkr7gy7ZTfApFfI-Xxt1gZNtsDDiXoXOXc0OrkyFs&m=W2jEgk2s_xjLOLC-j8lPBnwVgteHS0-yYEGMqin16nmfzndzNgBE9mEvtbvyVzQo&s=zU-TBR-xTsKRXEW5gdgL0WRRYBg7B7cbLluu65_PfkI&e=
> > , please
> > enclose %s within quotes:
> > _("'%s': Invalid file descriptor while waiting for monitor")
> Ack. Thanks.
> > > mon->goteof = true;
> > > }
> > > }
> > > @@ -609,13 +616,14 @@ qemuMonitorIO(GSocket *socket G_GNUC_UNUSED,
> > > virResetLastError();
> > > } else {
> > > if (virGetLastErrorCode() == VIR_ERR_OK && !mon->goteof)
> > > - virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> > > - _("Error while processing monitor IO"));
> > > + virReportError(VIR_ERR_INTERNAL_ERROR,
> > > + _("%s: Error while processing monitor
> > > IO"), NULLSTR(vmName));
> > Ditto.
> Ack.
> > > virCopyLastError(&mon->lastError);
> > > virResetLastError();
> > > }
> > >
> > > - VIR_DEBUG("Error on monitor %s",
> > > NULLSTR(mon->lastError.message));
> > > + VIR_DEBUG("Error on monitor %s mon=%p vm=%p name=%s",
> > > + NULLSTR(mon->lastError.message), mon, vm,
> > > NULLSTR(vmName));
> > > /* If IO process resulted in an error & we have a message,
> > > * then wakeup that waiter */
> > > if (mon->msg && !mon->msg->finished) {
> > > @@ -631,22 +639,22 @@ qemuMonitorIO(GSocket *socket G_GNUC_UNUSED,
> > > * will try to acquire the virDomainObj *mutex next */
> > > if (mon->goteof) {
> > > qemuMonitorEofNotifyCallback eofNotify = mon->cb->eofNotify;
> > > - virDomainObj *vm = mon->vm;
> > >
> > > /* Make sure anyone waiting wakes up now */
> > > virCondSignal(&mon->notify);
> > > virObjectUnlock(mon);
> > > - VIR_DEBUG("Triggering EOF callback");
> > > + VIR_DEBUG("Triggering EOF callback mon=%p vm=%p name=%s",
> > > + mon, vm, NULLSTR(vmName));
> > > (eofNotify)(mon, vm, mon->callbackOpaque);
> > > virObjectUnref(mon);
> > > } else if (error) {
> > > qemuMonitorErrorNotifyCallback errorNotify =
> > > mon->cb->errorNotify;
> > > - virDomainObj *vm = mon->vm;
> > >
> > > /* Make sure anyone waiting wakes up now */
> > > virCondSignal(&mon->notify);
> > > virObjectUnlock(mon);
> > > - VIR_DEBUG("Triggering error callback");
> > > + VIR_DEBUG("Triggering error callback mon=%p vm=%p name=%s",
> > > + mon, vm, NULLSTR(vmName));
> > > (errorNotify)(mon, vm, mon->callbackOpaque);
> > > virObjectUnref(mon);
> > > } else {
> > > @@ -694,6 +702,7 @@ qemuMonitorOpenInternal(virDomainObj *vm,
> > > mon->fd = fd;
> > > mon->context = g_main_context_ref(context);
> > > mon->vm = virObjectRef(vm);
> > > + mon->domainName = g_strdup(vm->def->name);
> > do not forget to g_free() this during cleanup in the same function.
> So, in cleanup: qemuMonitorDispose is called. And there I have added g_free()
> to clean mon->domainName.
No, in cleanup, I see qemuMonitorClose() is called where do you do not add
any additional code to free the allocation.
This is what I see in cleanup code:
```
cleanup:
/* We don't want the 'destroy' callback invoked during
* cleanup from construction failure, because that can
* give a double-unref on virDomainObj *in the caller,
* so kill the callbacks now.
*/
mon->cb = NULL;
/* The caller owns 'fd' on failure */
mon->fd = -1;
qemuMonitorClose(mon);
return NULL;
```
> >
> > > mon->waitGreeting = true;
> > > mon->cb = cb;
> > > mon->callbackOpaque = opaque;
> > > @@ -932,17 +941,19 @@ qemuMonitorSend(qemuMonitor *mon,
> > > qemuMonitorMessage *msg)
> > > {
> > > int ret = -1;
> > > + virDomainObj *vm = mon->vm;
> > > + char *vmName = mon->domainName;
> > >
> > > /* Check whether qemu quit unexpectedly */
> > > if (mon->lastError.code != VIR_ERR_OK) {
> > > - VIR_DEBUG("Attempt to send command while error is set %s",
> > > - NULLSTR(mon->lastError.message));
> > > + VIR_DEBUG("Attempt to send command while error is set %s mon=%p
> > > vm=%p name=%s",
> > > + NULLSTR(mon->lastError.message), mon, vm,
> > > NULLSTR(vmName));
> > > virSetError(&mon->lastError);
> > > return -1;
> > > }
> > > if (mon->goteof) {
> > > - virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> > > - _("End of file from qemu monitor"));
> > > + virReportError(VIR_ERR_INTERNAL_ERROR,
> > > + _("%s: End of file from qemu monitor"),
> > > NULLSTR(vmName));
> > ditto re error string format.
> Ack.
> >
> > > return -1;
> > > }
> > >
> > > @@ -955,15 +966,15 @@ qemuMonitorSend(qemuMonitor *mon,
> > >
> > > while (!mon->msg->finished) {
> > > if (virCondWait(&mon->notify, &mon->parent.lock) < 0) {
> > > - virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> > > - _("Unable to wait on monitor condition"));
> > > + virReportError(VIR_ERR_INTERNAL_ERROR,
> > > + _("%s: Unable to wait on monitor condition"),
> > > NULLSTR(vmName));
> > ditto as above.
> Ack.
> > > goto cleanup;
> > > }
> > > }
> > >
> > > if (mon->lastError.code != VIR_ERR_OK) {
> > > - VIR_DEBUG("Send command resulted in error %s",
> > > - NULLSTR(mon->lastError.message));
> > > + VIR_DEBUG("Send command resulted in error %s mon=%p vm=%p
> > > name=%s",
> > > + NULLSTR(mon->lastError.message), mon, vm,
> > > NULLSTR(vmName));
> > > virSetError(&mon->lastError);
> > > goto cleanup;
> > > }
> > > --
> > > 2.25.1
> > >
> > >
>
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