Bug 1763105

These two options are introduce since qemu 4.0:
https://github.com/qemu/qemu/commit/9b890bdcb6ec11868da92c1daeb51c69d9483da8

Patches: https://lists.nongnu.org/archive/html/qemu-block/2019-10/msg01254.html

QEMU has been recently split into sub-components and as a one-time operation to avoid breakage of tools, we are setting the QEMU sub-component of this BZ to "General". Please review and change the sub-component if necessary the next time you review this BZ. Thanks

I've resubmitted this change upstream: https://lists.gnu.org/archive/html/qemu-devel/2021-03/msg00280.html

I think the test case in the opening comment could be updated to something like this:

$ man qemu-img | grep data_file

Since it appears the options are documented with underscores.

This is now included in upstream as commit: d65173f924 "Document qemu-img options data_file and data_file_raw"

Move to RHEL since RHEL-AV will only be a rebuild of RHEL starting w/ 8.6.0

Added the RHEL rebase bz to depends on list

Verified this bug as below.


Tested with:
qemu-kvm-6.1.0-2.el9
kernel-5.14.0-0.rc7.54.el9.x86_64


Steps:
# man qemu-img
......
......
          data_file
                 Filename  where  all  guest  data  will be stored. If this option is used, the
                 qcow2 file will only contain the image's metadata.

                 Note: Data loss will occur if the given filename  already  exists  when  using
                 this  option  with  qemu-img  create  since qemu-img will create the data file
                 anew, overwriting the file's original contents. To simply update the reference
                 to point to the given pre-existing file, use qemu-img amend.

          data_file_raw
                 If this option is set to on, QEMU will always keep the external data file con‐
                 sistent as a standalone read-only raw image.

                 It does this by forwarding all write accesses to the qcow2 file through to the
                 raw data file, including their offsets. Therefore, data that is visible on the
                 qcow2 node (i.e., to the guest) at some offset is visible at the  same  offset
                 in  the  raw data file. This results in a read-only raw image. Writes that by‐
                 pass the qcow2 metadata may corrupt the qcow2 metadata because the out-of-band
                 writes may result in the metadata falling out of sync with the raw image.

                 If  this  option is off, QEMU will use the data file to store data in an arbi‐
                 trary manner. The file’s content will not make sense without the  accompanying
                 qcow2  metadata.  Where data is written will have no relation to its offset as
                 seen by the guest, and some writes (specifically zero writes) may not be  for‐
                 warded  to  the  data file at all, but will only be handled by modifying qcow2
                 metadata.

                 This option can only be enabled if data_file is set.
.......

(In reply to Tingting Mao from comment #12)
> Verified this bug as below.
> 
> 
> Tested with:
> qemu-kvm-6.1.0-2.el9
> kernel-5.14.0-0.rc7.54.el9.x86_64
> 
Sorry. The env should be:
qemu-kvm-6.1.0-1.module+el8.6.0+12648+6ede71a5
kernel-4.18.0-342.el8.x86_64

> 
> Steps:
> # man qemu-img
> ......
> ......
>           data_file
>                  Filename  where  all  guest  data  will be stored. If this
> option is used, the
>                  qcow2 file will only contain the image's metadata.
> 
>                  Note: Data loss will occur if the given filename  already 
> exists  when  using
>                  this  option  with  qemu-img  create  since qemu-img will
> create the data file
>                  anew, overwriting the file's original contents. To simply
> update the reference
>                  to point to the given pre-existing file, use qemu-img amend.
> 
>           data_file_raw
>                  If this option is set to on, QEMU will always keep the
> external data file con‐
>                  sistent as a standalone read-only raw image.
> 
>                  It does this by forwarding all write accesses to the qcow2
> file through to the
>                  raw data file, including their offsets. Therefore, data
> that is visible on the
>                  qcow2 node (i.e., to the guest) at some offset is visible
> at the  same  offset
>                  in  the  raw data file. This results in a read-only raw
> image. Writes that by‐
>                  pass the qcow2 metadata may corrupt the qcow2 metadata
> because the out-of-band
>                  writes may result in the metadata falling out of sync with
> the raw image.
> 
>                  If  this  option is off, QEMU will use the data file to
> store data in an arbi‐
>                  trary manner. The file’s content will not make sense
> without the  accompanying
>                  qcow2  metadata.  Where data is written will have no
> relation to its offset as
>                  seen by the guest, and some writes (specifically zero
> writes) may not be  for‐
>                  warded  to  the  data file at all, but will only be handled
> by modifying qcow2
>                  metadata.
> 
>                  This option can only be enabled if data_file is set.
> .......