From: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>
Date: Fri, 9 Nov 2018 07:50:47 +0000 (+0300)
Subject: qemu: disable external snapshot of readonly disk
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=067aad26befafb446e8a0d5c83d1a4d3b7f704d9;p=libvirt.git

qemu: disable external snapshot of readonly disk

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.

Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>
---

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index acba485309..d0cf2c115a 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -14755,6 +14755,13 @@ 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;