[libvirt] [PATCH v1] qemu-migration: Disallow migration of read only disk

[Koniszewski, Pawel]

> -----Original Message-----
> From: libvir-list-bounces at redhat.com [mailto:libvir-list-
> bounces at redhat.com] On Behalf Of Corey S. McQuay
> Sent: Friday, August 5, 2016 8:34 PM
> To: jjherne at linux.vnet.ibm.com; libvir-list at redhat.com
> Cc: Corey S. McQuay <csmcquay at linux.vnet.ibm.com>
> Subject: [libvirt] [PATCH v1] qemu-migration: Disallow migration of read only
> disk
> 
> From: "Corey S. McQuay" <csmcquay at linux.vnet.ibm.com>
> 
> Currently Libvirt allows attempts to migrate read only disks. Qemu cannot
> handle this as read only disks cannot be written to on the destination system.
> The end result is a cryptic error message and a failed migration.
> 
> This patch causes migration to fail earlier and provides a meaningful error
> message stating that migrating read only disks is not supported.

What will happen if read-only disk is copied to destination prior to migration start? Currently such scenario works, will it still work with this code?

> Signed-off-by: Corey S. McQuay <csmcquay at linux.vnet.ibm.com>
> Reviewed-by: Jason J. Herne <jjherne at linux.vnet.ibm.com>
> Reviewed-by: Boris Fiuczynski <fiuczy at linux.vnet.ibm.com>
> ---
>  src/qemu/qemu_migration.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> index d018add..7d0a78f 100644
> --- a/src/qemu/qemu_migration.c
> +++ b/src/qemu/qemu_migration.c
> @@ -2387,6 +2387,28 @@ qemuMigrationIsSafe(virDomainDefPtr def,
>      return true;
>  }
> 
> +static bool
> +qemuMigrationAreAllDisksRW(virDomainDefPtr def,
> +                    size_t nmigrate_disks,
> +                    const char **migrate_disks) {
> +    size_t i;
> +
> +    for (i = 0; i < def->ndisks; i++) {
> +        virDomainDiskDefPtr disk = def->disks[i];
> +
> +        if (qemuMigrateDisk(disk, nmigrate_disks, migrate_disks) &&
> +            disk->src->readonly) {
> +            virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
> +                       _("Cannot migrate read-only disk %s"),
> +                       disk->dst);
> +            return false;
> +        }
> +    }
> +
> +    return true;
> +}
> +
>  /** qemuMigrationSetOffline
>   * Pause domain for non-live migration.
>   */
> @@ -3132,6 +3154,9 @@ qemuMigrationBeginPhase(virQEMUDriverPtr
> driver,
>          !qemuMigrationIsSafe(vm->def, nmigrate_disks, migrate_disks))
>          goto cleanup;
> 
> +    if (!qemuMigrationAreAllDisksRW(vm->def, nmigrate_disks,
> migrate_disks))
> +        goto cleanup;
> +
>      if (flags & VIR_MIGRATE_POSTCOPY &&
>          (!(flags & VIR_MIGRATE_LIVE) ||
>           flags & VIR_MIGRATE_PAUSED)) {
> --
> 1.8.3.1
> 
> --
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