Re: [libvirt] [PATCH] qemu: blockCopy: Allow shallow block copy into a raw image

2015-04-28 Thread Eric Blake 
On 04/27/2015 10:08 PM, Shanzhi Yu wrote:
 Should libvirt post error when try a shallow blockcopy of file without
 backing file, just as shallow blockcommit?
 I cannot reproduce the error above, could you please post steps to do
 that? or perhaps debug log from libvirt?
 
 It is easy to reproduce. Suppose live guest xml looks like:
 
 # virsh dumpxml vm1|grep disk -A 8
 disk type='file' device='disk'
   driver name='qemu' type='qcow2'/
   source file='/var/lib/libvirt/images/raw.1430143276'/
   backingStore type='file' index='1'
 format type='raw'/
 source file='/var/lib/libvirt/images/raw.img'/
 backingStore/
   /backingStore
   target dev='vda' bus='virtio'/
   alias name='virtio-disk0'/
   address type='pci' domain='0x' bus='0x00' slot='0x03'
 function='0x0'/
 /disk
 
 Then try a shallow blockcommit of file has no backing file
 

 But a shallow block copy of file which has backing file into a raw  file
 does not make any sense, right?

A shallow block copy of:

A - B

into a pre-existing file C, where C starts life with contents identical
to A, makes sense.

A shallow block copy where _libvirt_ creates C does not make sense.  The
key is that the moment you use the REUSE_EXTERNAL flag, _you_ are now
responsible for providing a valid destination (and anything is
supported; libvirt should not get in your way).

-- 
Eric Blake   eblake redhat com+1-919-301-3266
Libvirt virtualization library http://libvirt.org



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Re: [libvirt] [PATCH] qemu: blockCopy: Allow shallow block copy into a raw image

2015-04-27 Thread Shanzhi Yu 


On 04/27/2015 08:01 PM, Peter Krempa wrote:
 The documentation states that for shallow block copy the image has to
 have the same guest visible content as backing file of the current
 image. This condition can be achieved also with a raw file (or a qcow
 without a backing file) so remove the condition that would disallow it.

 (This patch additionally fixes crash described in
  https://bugzilla.redhat.com/show_bug.cgi?id=1215569 since it removes
  the code)
 ---
  src/qemu/qemu_driver.c | 10 --
  1 file changed, 10 deletions(-)

 diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
 index 70bf7aa..f979d33 100644
 --- a/src/qemu/qemu_driver.c
 +++ b/src/qemu/qemu_driver.c
 @@ -16815,16 +16815,6 @@ qemuDomainBlockCopyCommon(virDomainObjPtr vm,
  if (qemuDomainDetermineDiskChain(driver, vm, disk, false, true)  0)
  goto endjob;

 -if ((flags  VIR_DOMAIN_BLOCK_COPY_SHALLOW) 
 -mirror-format == VIR_STORAGE_FILE_RAW 
 -disk-src-backingStore-path) {
 -virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
 -   _(disk '%s' has backing file, so raw shallow copy 
 - is not possible),
 -   disk-dst);
 -goto endjob;
 -}
 -

Although a shallow blockcopy of file without backing file is
semantically correct, but still feel a little weird.
And, a shallow blockcommit of file without backing file will failed with
error
error: invalid argument: top '/var/lib/libvirt/images/raw.img' in chain
for 'vda' has no backing file

Should libvirt post error when try a shallow blockcopy of file without
backing file, just as shallow blockcommit?

  /* Prepare the destination file.  */
  /* XXX Allow non-file mirror destinations */
  if (!virStorageSourceIsLocalStorage(mirror)) {

-- 
Regards
shyu

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Re: [libvirt] [PATCH] qemu: blockCopy: Allow shallow block copy into a raw image

2015-04-27 Thread Shanzhi Yu 


On 04/27/2015 11:38 PM, Peter Krempa wrote:
 On Mon, Apr 27, 2015 at 22:11:40 +0800, Shanzhi Yu wrote:

 On 04/27/2015 08:01 PM, Peter Krempa wrote:
 The documentation states that for shallow block copy the image has to
 have the same guest visible content as backing file of the current
 image. This condition can be achieved also with a raw file (or a qcow
 without a backing file) so remove the condition that would disallow it.

 (This patch additionally fixes crash described in
  https://bugzilla.redhat.com/show_bug.cgi?id=1215569 since it removes
  the code)
 ---
  src/qemu/qemu_driver.c | 10 --
  1 file changed, 10 deletions(-)

 diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
 index 70bf7aa..f979d33 100644
 --- a/src/qemu/qemu_driver.c
 +++ b/src/qemu/qemu_driver.c
 @@ -16815,16 +16815,6 @@ qemuDomainBlockCopyCommon(virDomainObjPtr vm,
  if (qemuDomainDetermineDiskChain(driver, vm, disk, false, true)  0)
  goto endjob;

 -if ((flags  VIR_DOMAIN_BLOCK_COPY_SHALLOW) 
 -mirror-format == VIR_STORAGE_FILE_RAW 
 -disk-src-backingStore-path) {
 -virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
 -   _(disk '%s' has backing file, so raw shallow copy 
 - is not possible),
 -   disk-dst);
 -goto endjob;
 -}
 -
 Although a shallow blockcopy of file without backing file is
 semantically correct, but still feel a little weird.
 And, a shallow blockcommit of file without backing file will failed with
 error
 error: invalid argument: top '/var/lib/libvirt/images/raw.img' in chain
 for 'vda' has no backing file

 Should libvirt post error when try a shallow blockcopy of file without
 backing file, just as shallow blockcommit?
 I cannot reproduce the error above, could you please post steps to do
 that? or perhaps debug log from libvirt?

It is easy to reproduce. Suppose live guest xml looks like:

# virsh dumpxml vm1|grep disk -A 8
disk type='file' device='disk'
  driver name='qemu' type='qcow2'/
  source file='/var/lib/libvirt/images/raw.1430143276'/
  backingStore type='file' index='1'
format type='raw'/
source file='/var/lib/libvirt/images/raw.img'/
backingStore/
  /backingStore
  target dev='vda' bus='virtio'/
  alias name='virtio-disk0'/
  address type='pci' domain='0x' bus='0x00' slot='0x03'
function='0x0'/
/disk

Then try a shallow blockcommit of file has no backing file

# virsh blockcommit vm1 vda --top vda[1] --shallow
error: invalid argument: top '/var/lib/libvirt/images/raw.img' in chain
for 'vda' has no backing file



 When copying from a single layer image with the --shallow flag I'm able
 to successfully copy both into a raw and a qcow2 file.

I also can do it.
But a shallow block copy of file which has backing file into a raw  file
does not make any sense, right?

  /* Prepare the destination file.  */
  /* XXX Allow non-file mirror destinations */
  if (!virStorageSourceIsLocalStorage(mirror)) {
 Peter

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shyu

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Re: [libvirt] [PATCH] qemu: blockCopy: Allow shallow block copy into a raw image

2015-04-27 Thread Peter Krempa 
On Mon, Apr 27, 2015 at 22:11:40 +0800, Shanzhi Yu wrote:
 
 
 On 04/27/2015 08:01 PM, Peter Krempa wrote:
  The documentation states that for shallow block copy the image has to
  have the same guest visible content as backing file of the current
  image. This condition can be achieved also with a raw file (or a qcow
  without a backing file) so remove the condition that would disallow it.
 
  (This patch additionally fixes crash described in
   https://bugzilla.redhat.com/show_bug.cgi?id=1215569 since it removes
   the code)
  ---
   src/qemu/qemu_driver.c | 10 --
   1 file changed, 10 deletions(-)
 
  diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
  index 70bf7aa..f979d33 100644
  --- a/src/qemu/qemu_driver.c
  +++ b/src/qemu/qemu_driver.c
  @@ -16815,16 +16815,6 @@ qemuDomainBlockCopyCommon(virDomainObjPtr vm,
   if (qemuDomainDetermineDiskChain(driver, vm, disk, false, true)  0)
   goto endjob;
 
  -if ((flags  VIR_DOMAIN_BLOCK_COPY_SHALLOW) 
  -mirror-format == VIR_STORAGE_FILE_RAW 
  -disk-src-backingStore-path) {
  -virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
  -   _(disk '%s' has backing file, so raw shallow copy 
  - is not possible),
  -   disk-dst);
  -goto endjob;
  -}
  -
 
 Although a shallow blockcopy of file without backing file is
 semantically correct, but still feel a little weird.
 And, a shallow blockcommit of file without backing file will failed with
 error
 error: invalid argument: top '/var/lib/libvirt/images/raw.img' in chain
 for 'vda' has no backing file
 
 Should libvirt post error when try a shallow blockcopy of file without
 backing file, just as shallow blockcommit?

I cannot reproduce the error above, could you please post steps to do
that? or perhaps debug log from libvirt?

When copying from a single layer image with the --shallow flag I'm able
to successfully copy both into a raw and a qcow2 file.

 
   /* Prepare the destination file.  */
   /* XXX Allow non-file mirror destinations */
   if (!virStorageSourceIsLocalStorage(mirror)) {

Peter


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Re: [libvirt] [PATCH] qemu: blockCopy: Allow shallow block copy into a raw image

2015-04-27 Thread Eric Blake 
On 04/27/2015 06:01 AM, Peter Krempa wrote:
 The documentation states that for shallow block copy the image has to
 have the same guest visible content as backing file of the current
 image. This condition can be achieved also with a raw file (or a qcow
 without a backing file) so remove the condition that would disallow it.
 
 (This patch additionally fixes crash described in
  https://bugzilla.redhat.com/show_bug.cgi?id=1215569 since it removes
  the code)
 ---
  src/qemu/qemu_driver.c | 10 --
  1 file changed, 10 deletions(-)

This removes a bit of a safety valve that tries to prevent users from
accidentally creating corrupt images when they use the API incorrectly,
but as the safety valve didn't always work and we could actually crash,
and as the documentation has already warned the user about using it
correctly, I can probably live with it.

 
 diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
 index 70bf7aa..f979d33 100644
 --- a/src/qemu/qemu_driver.c
 +++ b/src/qemu/qemu_driver.c
 @@ -16815,16 +16815,6 @@ qemuDomainBlockCopyCommon(virDomainObjPtr vm,
  if (qemuDomainDetermineDiskChain(driver, vm, disk, false, true)  0)
  goto endjob;
 
 -if ((flags  VIR_DOMAIN_BLOCK_COPY_SHALLOW) 
 -mirror-format == VIR_STORAGE_FILE_RAW 
 -disk-src-backingStore-path) {
 -virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
 -   _(disk '%s' has backing file, so raw shallow copy 
 - is not possible),
 -   disk-dst);
 -goto endjob;
 -}

However, one thing I'm not sure about: a shallow block copy with the
REUSE_EXTERNAL flag always makes sense (raw or not, because the user of
that flag knows what they are doing).  But a shallow block copy without
reusing an external file does not make sense - if libvirt is creating
the destination file, then we KNOW that the destination file does not
match the guest contents (except for the corner case where the guest is
not using the block and therefore it remains in the default state of all
0s because it is unwritten).  I'm not convinced yet that this is the
right patch.

-- 
Eric Blake   eblake redhat com+1-919-301-3266
Libvirt virtualization library http://libvirt.org



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