>>> On 7/29/2014 at 11:47 PM, in message <53D7C1F6.4030705@xxxxxxxxxx>, Eric Blake
<eblake@xxxxxxxxxx> wrote:
> On 07/29/2014 07:37 AM, Eric Blake wrote:
> > On 07/29/2014 03:59 AM, Chunyan Liu wrote:
> >> Check whether dst is the same device as source, if yes, report
> >> error and exit.
> >>
> >> Currently if dst is the same device as source, blockcopy is still
> >> going and qemu 'drive-mirror' is executed. Considering that:
> >> a). blockcopy to the same device is meaningless. b.) result is
> >> unexpected. (tested with block device whose source path is /dev/sdaX,
> >> after blockcopy, shutdown VM and then create VM from xml again, the
> >> VM cannot be started.) This case should not be allowed.
> >>
> >> Signed-off-by: Chunyan Liu <cyliu@xxxxxxxx>
> >> ---
> >> 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 704ba39..87a3790 100644
> >> --- a/src/qemu/qemu_driver.c
> >> +++ b/src/qemu/qemu_driver.c
> >> @@ -15309,6 +15309,13 @@ qemuDomainBlockCopy(virDomainObjPtr vm,
> >> }
> >>
> >> /* Prepare the destination file. */
> >> + if (STREQ(disk->src->path, dest)) {
> >
> > STREQ is too weak (consider symlinks, or even "a/b" vs. "a//b"). It
> > will catch some cases, but not all.
> >
> > I don't know that we can reliably detect all possible ways the user can
> > shoot themselves in the foot, so I'm not sure this patch is a good idea.
>
> A better idea would be to rely on the volume lease manager - obtaining a
> lease should be impossible for an image already in use (and should even
> cover the case of copying 'base <- active' onto 'base', which your
> equality test wouldn't catch). I'm not sure why the lease manager is not
> already flagging this issue - are we still using the nop lease manager
> by default, and would the fcntl or sanlock lease manager do a better job?
Besides the default lock is 'nop', currently lock manager is only used in:
VM start/stop and attach/detach disk, blockcopy not using it.
To use it in blockcopy, maybe can refer to attach/detach disk: before doing
blockcopy, try AcquireResource; after blockcopy finish, try releaseResource.
Anyway, using lock manager is a better idea in such cases.
>
> --
> Eric Blake eblake redhat com +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
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