[libvirt] [PATCH] snapshot: detect when qemu lacks disk-snapshot support
Noticed when testing new libvirt against old qemu that lacked the snapshot_blkdev HMP command. Libvirt was mistakenly treating the command as successful, and re-writing the domain XML to use the just-created 0-byte file, rendering the domain broken on restart. * src/qemu/qemu_monitor_text.c (qemuMonitorTextDiskSnapshot): Notice another possible error message. --- src/qemu/qemu_monitor_text.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/src/qemu/qemu_monitor_text.c b/src/qemu/qemu_monitor_text.c index 2f31d99..4774df9 100644 --- a/src/qemu/qemu_monitor_text.c +++ b/src/qemu/qemu_monitor_text.c @@ -3064,7 +3064,8 @@ qemuMonitorTextDiskSnapshot(qemuMonitorPtr mon, const char *device, goto cleanup; } - if (strstr(reply, "error while creating qcow2") != NULL) { + if (strstr(reply, "error while creating qcow2") != NULL || + strstr(reply, "unknown command:") != NULL) { qemuReportError(VIR_ERR_OPERATION_FAILED, _("Failed to take snapshot: %s"), reply); goto cleanup; -- 1.7.4.4
On 10/18/2011 03:51 PM, Eric Blake wrote:
Noticed when testing new libvirt against old qemu that lacked the snapshot_blkdev HMP command. Libvirt was mistakenly treating the command as successful, and re-writing the domain XML to use the just-created 0-byte file, rendering the domain broken on restart.
* src/qemu/qemu_monitor_text.c (qemuMonitorTextDiskSnapshot): Notice another possible error message. --- src/qemu/qemu_monitor_text.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-)
Phooey - testing reveals that this fixes the main problem (the command now fails with a nice error without corrupting the domain xml: # virsh snapshot-create --disk-only dom error: operation failed: Failed to take snapshot: unknown command: 'snapshot_blkdev' ), but isn't quite perfect (the 0-byte file is still left behind). v2 coming up soon. -- Eric Blake eblake@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org
Noticed when testing new libvirt against old qemu that lacked the snapshot_blkdev HMP command. Libvirt was mistakenly treating the command as successful, and re-writing the domain XML to use the just-created 0-byte file, rendering the domain broken on restart. * src/qemu/qemu_monitor_text.c (qemuMonitorTextDiskSnapshot): Notice another possible error message. * src/qemu/qemu_driver.c (qemuDomainSnapshotCreateSingleDiskActive): Don't keep 0-byte file on failure. --- v2: clean up on failure src/qemu/qemu_driver.c | 2 +- src/qemu/qemu_monitor_text.c | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index f833655..84ef4dd 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -9027,7 +9027,6 @@ qemuDomainSnapshotCreateSingleDiskActive(struct qemud_driver *driver, VIR_WARN("Unable to release lock on %s", source); goto cleanup; } - need_unlink = false; disk->src = origsrc; origsrc = NULL; @@ -9041,6 +9040,7 @@ qemuDomainSnapshotCreateSingleDiskActive(struct qemud_driver *driver, goto cleanup; /* Update vm in place to match changes. */ + need_unlink = false; VIR_FREE(disk->src); disk->src = source; source = NULL; diff --git a/src/qemu/qemu_monitor_text.c b/src/qemu/qemu_monitor_text.c index 2f31d99..4774df9 100644 --- a/src/qemu/qemu_monitor_text.c +++ b/src/qemu/qemu_monitor_text.c @@ -3064,7 +3064,8 @@ qemuMonitorTextDiskSnapshot(qemuMonitorPtr mon, const char *device, goto cleanup; } - if (strstr(reply, "error while creating qcow2") != NULL) { + if (strstr(reply, "error while creating qcow2") != NULL || + strstr(reply, "unknown command:") != NULL) { qemuReportError(VIR_ERR_OPERATION_FAILED, _("Failed to take snapshot: %s"), reply); goto cleanup; -- 1.7.4.4
On Tue, Oct 18, 2011 at 04:04:57PM -0600, Eric Blake wrote:
Noticed when testing new libvirt against old qemu that lacked the snapshot_blkdev HMP command. Libvirt was mistakenly treating the command as successful, and re-writing the domain XML to use the just-created 0-byte file, rendering the domain broken on restart.
* src/qemu/qemu_monitor_text.c (qemuMonitorTextDiskSnapshot): Notice another possible error message. * src/qemu/qemu_driver.c (qemuDomainSnapshotCreateSingleDiskActive): Don't keep 0-byte file on failure. ---
v2: clean up on failure
src/qemu/qemu_driver.c | 2 +- src/qemu/qemu_monitor_text.c | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index f833655..84ef4dd 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -9027,7 +9027,6 @@ qemuDomainSnapshotCreateSingleDiskActive(struct qemud_driver *driver, VIR_WARN("Unable to release lock on %s", source); goto cleanup; } - need_unlink = false;
disk->src = origsrc; origsrc = NULL; @@ -9041,6 +9040,7 @@ qemuDomainSnapshotCreateSingleDiskActive(struct qemud_driver *driver, goto cleanup;
/* Update vm in place to match changes. */ + need_unlink = false; VIR_FREE(disk->src); disk->src = source; source = NULL; diff --git a/src/qemu/qemu_monitor_text.c b/src/qemu/qemu_monitor_text.c index 2f31d99..4774df9 100644 --- a/src/qemu/qemu_monitor_text.c +++ b/src/qemu/qemu_monitor_text.c @@ -3064,7 +3064,8 @@ qemuMonitorTextDiskSnapshot(qemuMonitorPtr mon, const char *device, goto cleanup; }
- if (strstr(reply, "error while creating qcow2") != NULL) { + if (strstr(reply, "error while creating qcow2") != NULL || + strstr(reply, "unknown command:") != NULL) { qemuReportError(VIR_ERR_OPERATION_FAILED, _("Failed to take snapshot: %s"), reply); goto cleanup; -- 1.7.4.4
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ACK, snapshot still works correctly when qemu does support it, and after review with Eric, I think the code looks good. Dave
On 10/18/2011 05:31 PM, Dave Allan wrote:
On Tue, Oct 18, 2011 at 04:04:57PM -0600, Eric Blake wrote:
Noticed when testing new libvirt against old qemu that lacked the snapshot_blkdev HMP command. Libvirt was mistakenly treating the command as successful, and re-writing the domain XML to use the just-created 0-byte file, rendering the domain broken on restart.
* src/qemu/qemu_monitor_text.c (qemuMonitorTextDiskSnapshot): Notice another possible error message. * src/qemu/qemu_driver.c (qemuDomainSnapshotCreateSingleDiskActive): Don't keep 0-byte file on failure.
ACK, snapshot still works correctly when qemu does support it, and after review with Eric, I think the code looks good.
Thanks; pushed. -- Eric Blake eblake@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org
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Eric Blake