[libvirt] [PATCH RFC 08/22] qemu_process: Persist stderr in qemuProcess struct

[Jiri Denemark]

On Sun, Nov 11, 2018 at 13:59:16 -0600, Chris Venteicher wrote:
> A qemuProcess struct tracks the entire lifespan of a single QEMU Process
> including storing error output when the process terminates or activation
> fails.
> 
> Error output remains available until qemuProcessFree is called.
> 
> The qmperr buffer no longer needs to be maintained outside of the
> qemuProcess structure because the structure is used for a single QEMU
> process and the structures can be maintained as long as required
> to retrieve the process error info.
> 
> Capabilities init code is refactored but continues to report QEMU
> process error data only when the initial (non KVM) QEMU process activation

As explained for the previous patch the initial QEMU process actually
checks KVM if available.

> fails to result in a usable monitor connection for retrieving
> capabilities.
> 
> The VIR_ERR_INTERNAL_ERROR "Failed to probe QEMU binary" reporting is
> moved into virQEMUCapsInitQMP function and the stderr string is
> extracted from the qemuProcess struct using a macro to retrieve the
> string.
> 
> The same error and log message should be generated, in the same
> conditions, after this patch as before.
> 
> Signed-off-by: Chris Venteicher <cventeic at redhat.com>
> ---
>  src/qemu/qemu_capabilities.c | 27 ++++++++++++---------------
>  src/qemu/qemu_process.c      | 12 ++++--------
>  src/qemu/qemu_process.h      |  6 ++++--
>  3 files changed, 20 insertions(+), 25 deletions(-)
> 
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index a957c3bdbd..f5e327097e 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -4216,8 +4216,7 @@ static int
>  virQEMUCapsInitQMP(virQEMUCapsPtr qemuCaps,
>                     const char *libDir,
>                     uid_t runUid,
> -                   gid_t runGid,
> -                   char **qmperr)
> +                   gid_t runGid)

Yes, hiding qmperror inside virQEMUCapsInitQMP (actually inside the new
function which will be introduced once virQEMUCapsInitQMP is refactored
as I suggested in my review for the previous patch) is definitely a good
idea.

>  {
>      qemuProcessPtr proc = NULL;
>      qemuProcessPtr proc_kvm = NULL;
> @@ -4226,7 +4225,7 @@ virQEMUCapsInitQMP(virQEMUCapsPtr qemuCaps,
>      bool forceTCG = false;
>  
>      if (!(proc = qemuProcessNew(qemuCaps->binary, libDir,
> -                                runUid, runGid, qmperr, forceTCG)))
> +                                runUid, runGid, forceTCG)))
>          goto cleanup;

The new function can just return directly from here...

>  
>      if ((rc = qemuProcessRun(proc)) != 0) {
> @@ -4242,7 +4241,7 @@ virQEMUCapsInitQMP(virQEMUCapsPtr qemuCaps,
>          qemuProcessStopQmp(proc);
>  
>          forceTCG = true;
> -        proc_kvm = qemuProcessNew(qemuCaps->binary, libDir, runUid, runGid, NULL, forceTCG);
> +        proc_kvm = qemuProcessNew(qemuCaps->binary, libDir, runUid, runGid, forceTCG);
>  
>          if ((rc = qemuProcessRun(proc_kvm)) != 0) {
>              if (rc == 1)
> @@ -4257,6 +4256,13 @@ virQEMUCapsInitQMP(virQEMUCapsPtr qemuCaps,
>      ret = 0;
>  
>   cleanup:
> +    if (proc && !proc->mon) {

... which means you wouldn't need to check for proc at this point.

> +        char *err = QEMU_PROCESS_ERROR(proc) ? QEMU_PROCESS_ERROR(proc) : _("unknown error");

But even now you don't need to check for proc inside the macro. Which
makes the main (though still very tiny) reason for introducing the
macro. In other words, just drop the macro and use proc->qmperr
directly.

> +
> +        virReportError(VIR_ERR_INTERNAL_ERROR,
> +                       _("Failed to probe QEMU binary with QMP: %s"), err);
> +    }

And this would report an error even if ret == 0.

> +
>      qemuProcessStopQmp(proc);
>      qemuProcessStopQmp(proc_kvm);
>      qemuProcessFree(proc);
> @@ -4296,7 +4302,6 @@ virQEMUCapsNewForBinaryInternal(virArch hostArch,
>  {
>      virQEMUCapsPtr qemuCaps;
>      struct stat sb;
> -    char *qmperr = NULL;
>  
>      if (!(qemuCaps = virQEMUCapsNew()))
>          goto error;
> @@ -4323,15 +4328,8 @@ virQEMUCapsNewForBinaryInternal(virArch hostArch,
>          goto error;
>      }
>  
> -    if (virQEMUCapsInitQMP(qemuCaps, libDir, runUid, runGid, &qmperr) < 0) {
> -        virQEMUCapsLogProbeFailure(binary);
> -        goto error;
> -    }
> -
> -    if (!qemuCaps->usedQMP) {
> -        virReportError(VIR_ERR_INTERNAL_ERROR,
> -                       _("Failed to probe QEMU binary with QMP: %s"),
> -                       qmperr ? qmperr : _("unknown error"));
> +    if (virQEMUCapsInitQMP(qemuCaps, libDir, runUid, runGid) < 0 ||
> +        !qemuCaps->usedQMP) {

There should be no need to keep the !qemuCaps->usedQMP check after this
refactoring. See my notes to the next patch for more details.

>          virQEMUCapsLogProbeFailure(binary);
>          goto error;
>      }
> @@ -4350,7 +4348,6 @@ virQEMUCapsNewForBinaryInternal(virArch hostArch,
>      }
>  
>   cleanup:
> -    VIR_FREE(qmperr);
>      return qemuCaps;
>  
>   error:
...
> diff --git a/src/qemu/qemu_process.h b/src/qemu/qemu_process.h
> index ab2640ce7c..abd80baf5c 100644
> --- a/src/qemu/qemu_process.h
> +++ b/src/qemu/qemu_process.h
> @@ -220,7 +220,7 @@ struct _qemuProcess {
>      char *binary;
>      uid_t runUid;
>      gid_t runGid;
> -    char **qmperr;
> +    char *qmperr;  /* qemu process stderr */

You could even make the vairable name self-explanatory:
       char *stderr;

>      char *monarg;
>      char *monpath;
>      char *pidfile;
> @@ -232,11 +232,13 @@ struct _qemuProcess {
>      bool forceTCG;
>  };
>  
> +#define QEMU_PROCESS_ERROR(proc) \
> +   ((char *) (proc ? proc->qmperr: NULL))
> +

Just drop this.

>  qemuProcessPtr qemuProcessNew(const char *binary,
>                                const char *libDir,
>                                uid_t runUid,
>                                gid_t runGid,
> -                              char **qmperr,
>                                bool forceTCG);
>  
>  void qemuProcessFree(qemuProcessPtr proc);

Jirka