[libvirt PATCH v3 3/4] qemu_migration: get migration blockers before hardcoded checks

[Jiri Denemark]

On Wed, Jul 20, 2022 at 14:15:57 +0200, Eugenio Pérez wrote:
> since qemu 6.0, if migration is blocked for some reason, 'query-migrate'
> will return an array of error strings describing the migration blockers.
> This can be used to check whether there are any devices blocking
> migration, etc.
> 
> Enable qemuMigrationSrcIsAllowed to query it.
> 
> Signed-off-by: Eugenio Pérez <eperezma at redhat.com>
> ---
> v3:
> * Report message with a colon.
> * Report all blockers instead of only the first.
> ---
>  src/qemu/qemu_migration.c | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> index b12cb518ee..6ac4ef150b 100644
> --- a/src/qemu/qemu_migration.c
> +++ b/src/qemu/qemu_migration.c
> @@ -1414,6 +1414,20 @@ qemuMigrationSrcIsAllowedHostdev(const virDomainDef *def)
>      return true;
>  }
>  
> +static int
> +qemuDomainGetMigrationBlockers(virQEMUDriver *driver,
> +                               virDomainObj *vm,
> +                               char ***blockers)
> +{
> +    qemuDomainObjPrivate *priv = vm->privateData;
> +    int rc;
> +
> +    qemuDomainObjEnterMonitor(driver, vm);
> +    rc = qemuMonitorGetMigrationBlockers(priv->mon, blockers);
> +    qemuDomainObjExitMonitor(vm);
> +
> +    return rc;
> +}
>  
>  /**
>   * qemuMigrationSrcIsAllowed:
> @@ -1439,6 +1453,26 @@ qemuMigrationSrcIsAllowed(virQEMUDriver *driver,
>      int nsnapshots;
>      int pauseReason;
>      size_t i;
> +    int r;
> +
> +    /* Ask qemu if it have a migration blocker */
> +    if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_MIGRATION_BLOCKED_REASONS)) {
> +        g_auto(GStrv) blockers = NULL;
> +        r = qemuDomainGetMigrationBlockers(driver, vm, &blockers);
> +        if (r != 0) {
> +            virReportError(VIR_ERR_OPERATION_INVALID,
> +                           _("cannot migrate domain: %s"),
> +                           _("error getting blockers"));
> +            return false;
> +        }

As mentioned in v2 review the virReportError call should be dropped as
it overwrites the error reported by qemuDomainGetMigrationBlockers. That
is, you can just

    if (qemuDomainGetMigrationBlockers(driver, vm, &blockers) < 0)
        return false;

> +
> +        if (blockers && blockers[0]) {
> +            g_autofree char *reasons = g_strjoinv(", ", blockers);

In the following patch you change ", " to "; ". I don't mind that much
either way, but it should be done in this patch :-)

> +            virReportError(VIR_ERR_OPERATION_INVALID,
> +                           _("cannot migrate domain: %s"), reasons);
> +            return false;
> +        }
> +    }
>  
>      /* perform these checks only when migrating to remote hosts */
>      if (remote) {

Hmm, easy but not trivial changes so I guess v4 would be better.

Jirka