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Re: [libvirt] [PATCH] qemu-nbd: Deprecate qemu-nbd --partition



On Wed, Jan 23, 2019 at 15:19:53 -0600, Eric Blake wrote:
> The existing qemu-nbd --partition code claims to handle logical
> partitions up to 8, since its introduction in 2008 (commit 7a5ca86).
> However, the implementation is bogus (actual MBR logical partitions
> form a sort of linked list, with one partition per extended table
> entry, rather than four logical partitions in a single extended
> table), making the code unlikely to work for anything beyond -P5 on
> actual guest images. What's more, the code does not support GPT
> partitions, which are becoming more popular, and maintaining device
> subsetting in both NBD and the raw device is unnecessary maintenance
> burden.  And nbdkit has just added code to properly handle an
> arbitrary number of MBR partitions, along with its existing code
> for handling GPT partitions.
> 
> Note that obtaining the offsets of a partition can be learned by
> using 'qemu-nbd -c /dev/nbd0 file.qcow2 && sfdisk --dump /dev/nbd0',
> but by the time you've done that, you might as well just mount
> /dev/nbd0p1 that the kernel creates for you.
> 
> Start the clock on the deprecation cycle, with an example of how
> to write device subsetting without using -P.
> 
> Signed-off-by: Eric Blake <eblake redhat com>
> ---
>  qemu-deprecated.texi | 27 +++++++++++++++++++++++++++
>  qemu-nbd.texi        |  6 ++++--
>  qemu-nbd.c           |  2 ++
>  3 files changed, 33 insertions(+), 2 deletions(-)

Libvirt does not use qemu-nbd in any way so it's okay from our POV.

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