Re: [libvirt] [PATCH] snapshot: improve qemu handling of reused snapshot targets
On 03/20/2012 03:29 PM, Eric Blake wrote:
The oVirt developers have stated that the real reasons they want
to have qemu reuse existing volumes when creating a snapshot are:
1. the management framework is set up so that creation has to be
done from a central node for proper resource tracking, and having
libvirt and/or qemu create things violates the framework, and
2. qemu defaults to creating snapshots with an absolute path to
the backing file, but oVirt wants to manage a backing chain that
uses just relative names, to allow for easier migration of a chain
across storage locations.
/* create the stub file and set selinux labels; manipulate disk in
* place, in a way that can be reverted on failure. */
- fd = qemuOpenFile(driver, source, O_WRONLY | O_TRUNC | O_CREAT,
+ fd = qemuOpenFile(driver, source,
+ O_WRONLY | (reuse ? 0 : O_TRUNC | O_CREAT),
&need_unlink, NULL);
if (fd < 0)
goto cleanup;
I just realized this is a pointless open in the reuse case, since the
very next statement closes the fd (in other words, we are using open for
the side-effect of creation, but reuse says no creation is necessary).
I plan on squashing this:
diff --git i/src/qemu/qemu_driver.c w/src/qemu/qemu_driver.c
index ca81e75..4286b2a 100644
--- i/src/qemu/qemu_driver.c
+++ w/src/qemu/qemu_driver.c
@@ -9884,12 +9884,13 @@ qemuDomainSnapshotCreateSingleDiskActive(struct
qemud_driver *driver,
/* create the stub file and set selinux labels; manipulate disk in
* place, in a way that can be reverted on failure. */
- fd = qemuOpenFile(driver, source,
- O_WRONLY | (reuse ? 0 : O_TRUNC | O_CREAT),
- &need_unlink, NULL);
- if (fd < 0)
- goto cleanup;
- VIR_FORCE_CLOSE(fd);
+ if (!reuse) {
+ fd = qemuOpenFile(driver, source, O_WRONLY | O_TRUNC | O_CREAT,
+ &need_unlink, NULL);
+ if (fd < 0)
+ goto cleanup;
+ VIR_FORCE_CLOSE(fd);
+ }
origsrc = disk->src;
disk->src = source;
--
Eric Blake eblake(a)redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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