[libvirt] [PATCH v2] qemu: disable external snapshot of readonly disk

[Nikolay Shirokovskiy]

Disable external snapshot of readonly disk for inactive domains
as this operation is not very useful. As to active domains
such snapshot was not possible before already but error message was
not helpful so now it will be better.

Signed-off-by: Nikolay Shirokovskiy <***@virtuozzo.com>
---

Diff from v1 [1]
================

- move check to qemuDomainSnapshotPrepareDiskExternal
- disable such snapshot for inactive domain as well


[1] [PATCH] qemu: snapshot: better error for active external readonly disk
https://www.redhat.com/archives/libvir-list/2018-October/msg01322.html
continues in
https://www.redhat.com/archives/libvir-list/2018-November/msg00265.html


src/qemu/qemu_driver.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index a52e249..e747a5b 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -14514,6 +14514,13 @@ qemuDomainSnapshotPrepareDiskExternal(virDomainDiskDefPtr disk,
int ret = -1;
struct stat st;

+ if (disk->src->readonly) {
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+ _("external snapshot for readonly disk %s "
+ "is not supported"), disk->dst);
+ return -1;
+ }
+
if (qemuTranslateSnapshotDiskSourcePool(snapdisk) < 0)
return -1;

[John Ferlan]

Post by Nikolay Shirokovskiy
Disable external snapshot of readonly disk for inactive domains
as this operation is not very useful. As to active domains
such snapshot was not possible before already but error message was
not helpful so now it will be better.
---
Diff from v1 [1]
================
- move check to qemuDomainSnapshotPrepareDiskExternal
- disable such snapshot for inactive domain as well
[1] [PATCH] qemu: snapshot: better error for active external readonly disk
https://www.redhat.com/archives/libvir-list/2018-October/msg01322.html
continues in
https://www.redhat.com/archives/libvir-list/2018-November/msg00265.html
src/qemu/qemu_driver.c | 7 +++++++
1 file changed, 7 insertions(+)

Do you mind if I "merge" some details from the first patch on this to
generate the following commit message?:

Disable external snapshot of a readonly disk for domains as
this operation is not very useful. Such a snapshot is not
possible for active domains but the error message from QEMU
is more cryptic:

error: internal error: unable to execute QEMU command 'transaction':
Could not create file: Permission denied

This error at least makes the error more understandable for
active domains and disallows for inactive domains as well.


Reviewed-by: John Ferlan <***@redhat.com>

John