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Re: [libvirt] [PATCH v5 20/36] qemu_process: Enter QMP command mode when starting QEMU Process



On Sun, Dec 02, 2018 at 23:10:14 -0600, Chris Venteicher wrote:
> qemuProcessQmpStart starts a QEMU process and monitor connection that
> can be used by multiple functions possibly for multiple QMP commands.
> 
> The QMP exchange to exit capabilities negotiation mode and enter command mode
> can only be performed once after the monitor connection is established.
> 
> Move responsibility for entering QMP command mode into the qemuProcessQmp
> code so multiple functions can issue QMP commands in arbitrary orders.
> 
> This also simplifies the functions using the connection provided by
> qemuProcessQmpStart to issue QMP commands.
> 
> Test code now needs to call qemuMonitorSetCapabilities to send the
> message to switch to command mode because the test code does not use the
> qemuProcessQmp command that internally calls qemuMonitorSetCapabilities.
> 
> Signed-off-by: Chris Venteicher <cventeic redhat com>
> ---
>  src/qemu/qemu_capabilities.c | 12 ------------
>  src/qemu/qemu_process.c      |  8 ++++++++
>  tests/qemucapabilitiestest.c |  7 +++++++
>  3 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index ce60648897..038e3ecf7a 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -4035,12 +4035,6 @@ virQEMUCapsInitQMPMonitor(virQEMUCapsPtr qemuCaps,
>  
>      /* @mon is supposed to be locked by callee */
>  
> -    if (qemuMonitorSetCapabilities(mon) < 0) {
> -        VIR_DEBUG("Failed to set monitor capabilities %s",
> -                  virGetLastErrorMessage());
> -        goto cleanup;
> -    }
> -
>      if (qemuMonitorGetVersion(mon,
>                                &major, &minor, &micro,
>                                &package) < 0) {
> @@ -4213,12 +4207,6 @@ virQEMUCapsInitQMPMonitorTCG(virQEMUCapsPtr qemuCaps ATTRIBUTE_UNUSED,
>  {
>      int ret = -1;
>  
> -    if (qemuMonitorSetCapabilities(mon) < 0) {
> -        VIR_DEBUG("Failed to set monitor capabilities %s",
> -                  virGetLastErrorMessage());
> -        goto cleanup;
> -    }
> -
>      if (virQEMUCapsProbeQMPCPUDefinitions(qemuCaps, mon, true) < 0)
>          goto cleanup;
>  
> diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
> index 24945b1d17..80b938cc0b 100644
> --- a/src/qemu/qemu_process.c
> +++ b/src/qemu/qemu_process.c
> @@ -8332,6 +8332,14 @@ qemuProcessQmpConnectMonitor(qemuProcessQmpPtr proc)
>  
>      virObjectLock(proc->mon);
>  
> +    /* Exit capabilities negotiation mode and enter QEMU command mode
> +     * by issuing qmp_capabilities command to QEMU */
> +    if (qemuMonitorSetCapabilities(proc->mon) < 0) {
> +        VIR_DEBUG("Failed to set monitor capabilities %s",
> +                  virGetLastErrorMessage());
> +        goto cleanup;
> +    }
> +

It's quite unlikely, but we may eventually issue more commands to
initialize the monitor, which would require us to update the code in
qemucapabilitiestest.c again. Moreover, the test is supposed to test the
QEMU capabilities probing code rather than individual monitor commands.
Thus it should avoid direct qemuMonitor* calls.

For this reason, I think it would be better to separate this code into a
new function called qemuProcessQMPInitMonitor. And you can remove the
comment or transform it into a description of the new function. The new
function will be called from here and from qemucapabilitiestest.c. Thus
it cannot be static and its prototype should be placed in
src/qemu/qemu_processpriv.h since the function will be externally called
only from the test suite.

As a bonus, the code will be even more consistent with the VM startup
code, where qemuProcessInitMonitor is doing similar thing.

Jirka


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