[Qemu-devel] qemu-iotests 042: zero size image on VMDK

[Qemu-devel] qemu-iotests 042: zero size image on VMDK

[Fam Zheng]

Hi,

Currently VMDK block driver fails qemu-iotest case 042 because it
refuses to create block with zero size (silently). Is support for zero
size image desired or should this case be skipped?

    $ qemu-img create -f vmdk t.vmdk 0
    Formatting 't.vmdk', fmt=vmdk size=0 compat6=off 
    qemu-img: t.vmdk: error while creating vmdk: No such file or directory


-- 
Best regards,
Fam Zheng

Re: [Qemu-devel] qemu-iotests 042: zero size image on VMDK

[Stefan Hajnoczi]

On Thu, Apr 18, 2013 at 03:08:55PM +0800, Fam Zheng wrote:
> Currently VMDK block driver fails qemu-iotest case 042 because it
> refuses to create block with zero size (silently). Is support for zero
> size image desired or should this case be skipped?
> 
>     $ qemu-img create -f vmdk t.vmdk 0
>     Formatting 't.vmdk', fmt=vmdk size=0 compat6=off 
>     qemu-img: t.vmdk: error while creating vmdk: No such file or directory

Is there a reason to refuse 0-sized images?  The VMware tools can resize
images so it would be possible to grow them later (i.e. the use case is
weird but might still be valid).

It's also worth checking if VMware tools allow you to create 0-sized
image and whether they can operate on them.  If they fail to open or
inspect 0-sized images, then QEMU should not create them.

Stefan

Re: [Qemu-devel] qemu-iotests 042: zero size image on VMDK

[Fam Zheng]

On Thu, 04/18 09:39, Stefan Hajnoczi wrote:
> On Thu, Apr 18, 2013 at 03:08:55PM +0800, Fam Zheng wrote:
> > Currently VMDK block driver fails qemu-iotest case 042 because it
> > refuses to create block with zero size (silently). Is support for zero
> > size image desired or should this case be skipped?
> > 
> >     $ qemu-img create -f vmdk t.vmdk 0
> >     Formatting 't.vmdk', fmt=vmdk size=0 compat6=off 
> >     qemu-img: t.vmdk: error while creating vmdk: No such file or directory
> 
> Is there a reason to refuse 0-sized images?  The VMware tools can resize
> images so it would be possible to grow them later (i.e. the use case is
> weird but might still be valid).
> 
> It's also worth checking if VMware tools allow you to create 0-sized
> image and whether they can operate on them.  If they fail to open or
> inspect 0-sized images, then QEMU should not create them.

Not possible for VMware tools, either. See the vmware-vdiskmanager behavior here:

    $ ../vmdk.py t.vmdk resize 0
    OK

    $ ../vmdk.py t.vmdk show
    *** Header ***
                        magic : 1447904331
                      version : 1
                        flags : 3
                     capacity : 0
                   grain_size : 128
            descriptor_offset : 1
              descriptor_size : 20
              num_gtes_per_gt : 512
                   rgd_offset : 21
                    gd_offset : 278
                     overhead : 640
             unclean_shutdown : False
          single_endline_char : 

             non_endline_char :  
          double_endline_char : 
         double_endline_char2 : 

           compress_algorithm : 0
    *** Embeddd Descriptor ***
    # Disk DescriptorFile
    version=1
    encoding="UTF-8"
    CID=fffffffe
    parentCID=ffffffff
    isNativeSnapshot="no"
    createType="monolithicSparse"

    # Extent description
    RW 0 SPARSE "t.vmdk"

    # The Disk Data Base 
    #DDB

    ddb.deletable = "true"
    ddb.virtualHWVersion = "6"
    ddb.longContentID = "ff7abf4bda4302142e8ba8593ad0bdb6"
    ddb.uuid = "60 00 C2 94 2e a6 38 d0-8b 2c 21 37 49 8b 15 70"
    ddb.geometry.cylinders = "2048"
    ddb.geometry.heads = "64"
    ddb.geometry.sectors = "32"
    ddb.adapterType = "lsilogic"

    $ vmware-vdiskmanager -x 2G t.vmdk 
=>  Failed to open the disk 't.vmdk' : The file specified is not a virtual disk (0xf00003ebf).
    Failed to open disk 't.vmdk' : The file specified is not a virtual disk (0xf00003ebf).

=>  $ ../vmdk.py t.vmdk resize 1
    OK

    $ vmware-vdiskmanager -x 2G t.vmdk 
=>    Grow: 0% done.Disk expansion completed successfully.

    WARNING: If the virtual disk is partitioned, you must use a third-party
             utility in the virtual machine to expand the size of the
             partitions. For more information, see:
             http://www.vmware.com/support/kb/enduser/std_adp.php?p_faqid=1647


-- 
Fam

Re: [Qemu-devel] qemu-iotests 042: zero size image on VMDK

[Stefan Hajnoczi]

On Thu, Apr 18, 2013 at 12:08 PM, Fam Zheng <famz@redhat.com> wrote:
> On Thu, 04/18 09:39, Stefan Hajnoczi wrote:
>> On Thu, Apr 18, 2013 at 03:08:55PM +0800, Fam Zheng wrote:
>> > Currently VMDK block driver fails qemu-iotest case 042 because it
>> > refuses to create block with zero size (silently). Is support for zero
>> > size image desired or should this case be skipped?
>> >
>> >     $ qemu-img create -f vmdk t.vmdk 0
>> >     Formatting 't.vmdk', fmt=vmdk size=0 compat6=off
>> >     qemu-img: t.vmdk: error while creating vmdk: No such file or directory
>>
>> Is there a reason to refuse 0-sized images?  The VMware tools can resize
>> images so it would be possible to grow them later (i.e. the use case is
>> weird but might still be valid).
>>
>> It's also worth checking if VMware tools allow you to create 0-sized
>> image and whether they can operate on them.  If they fail to open or
>> inspect 0-sized images, then QEMU should not create them.
>
> Not possible for VMware tools, either. See the vmware-vdiskmanager behavior here:

There is a possibility that the vmdk.py script is "buggy".  Can you
use only VMware tools to create a 0-byte disk?

If the answer is yes, then there's a bug in vmdk.py and the vmdk block
driver should support creating 0-byte disks.

If no, then we should not allow it either.  This prevents confusion
when users find the qemu-img 0-byte VMDK does not work with VMware or
other tools.

Stefan

Re: [Qemu-devel] qemu-iotests 042: zero size image on VMDK

[Fam Zheng]

On Thu, 04/18 13:02, Stefan Hajnoczi wrote:
> On Thu, Apr 18, 2013 at 12:08 PM, Fam Zheng <famz@redhat.com> wrote:
> > On Thu, 04/18 09:39, Stefan Hajnoczi wrote:
> >> On Thu, Apr 18, 2013 at 03:08:55PM +0800, Fam Zheng wrote:
> >> > Currently VMDK block driver fails qemu-iotest case 042 because it
> >> > refuses to create block with zero size (silently). Is support for zero
> >> > size image desired or should this case be skipped?
> >> >
> >> >     $ qemu-img create -f vmdk t.vmdk 0
> >> >     Formatting 't.vmdk', fmt=vmdk size=0 compat6=off
> >> >     qemu-img: t.vmdk: error while creating vmdk: No such file or directory
> >>
> >> Is there a reason to refuse 0-sized images?  The VMware tools can resize
> >> images so it would be possible to grow them later (i.e. the use case is
> >> weird but might still be valid).
> >>
> >> It's also worth checking if VMware tools allow you to create 0-sized
> >> image and whether they can operate on them.  If they fail to open or
> >> inspect 0-sized images, then QEMU should not create them.
> >
> > Not possible for VMware tools, either. See the vmware-vdiskmanager behavior here:
> 
> There is a possibility that the vmdk.py script is "buggy".  Can you
> use only VMware tools to create a 0-byte disk?
> 
> If the answer is yes, then there's a bug in vmdk.py and the vmdk block
> driver should support creating 0-byte disks.
> 
> If no, then we should not allow it either.  This prevents confusion
> when users find the qemu-img 0-byte VMDK does not work with VMware or
> other tools.

Yep I forgot to mention, 1MB minimun applies for creating too.

    fam@localhost:~$ vmware-vdiskmanager -c -s 0 -t 0 t.vmdk -a lsilogic
    Either the disktype or the disksize is missing or is invalid.
    fam@localhost:~$ vmware-vdiskmanager -c -s 2048 -t 0 t.vmdk -a lsilogic
    Creating disk 't.vmdk'
    Virtual disk creation successful.

Also tried in Workstation GUI, where 0-byte disk can't be created either.

-- 
Fam