Re: [Qemu-devel] [PATCH v7 for 2.1 2/4] block: extend block-commit to accept a string for the backing file

[Kevin Wolf <kwolf@redhat.com>]

Am 25.06.2014 um 21:40 hat Jeff Cody geschrieben:
> On some image chains, QEMU may not always be able to resolve the
> filenames properly, when updating the backing file of an image
> after a block commit.
> 
> For instance, certain relative pathnames may fail, or drives may
> have been specified originally by file descriptor (e.g. /dev/fd/???),
> or a relative protocol pathname may have been used.
> 
> In these instances, QEMU may lack the information to be able to make
> the correct choice, but the user or management layer most likely does
> have that knowledge.
> 
> With this extension to the block-commit api, the user is able to change
> the backing file of the overlay image as part of the block-commit
> operation.
> 
> This allows the change to be 'safe', in the sense that if the attempt
> to write the overlay image metadata fails, then the block-commit
> operation returns failure, without disrupting the guest.
> 
> If the commit top is the active layer, then specifying the backing
> file string will be treated as an error (there is no overlay image
> to modify in that case).
> 
> If a backing file string is not specified in the command, the backing
> file string to use is determined in the same manner as it was
> previously.
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Jeff Cody <jcody@redhat.com>

Reviewed-by: Kevin Wolf <kwolf@redhat.com>