Re: [Qemu-devel] [PATCH] blockdev: Refuse to drive_del something added with blockdev-add

[Kevin Wolf]

Am 11.09.2014 um 16:45 hat Markus Armbruster geschrieben:
> For some device models, the guest can prevent unplug.  Some users need a
> way to forcibly revoke device model access to the block backend then, so
> the underlying images can be safely used for something else.
> 
> drive_del lets you do that.  Unfortunately, it conflates revoking access
> with destroying the backend.
> 
> Commit 9063f81 made drive_del immediately destroy the root BDS.  Nice:
> the device name becomes available for reuse immediately.  Not so nice:
> the device model's pointer to the root BDS dangles, and we're prone to
> crash when the memory gets reused.
> 
> Commit d22b2f4 fixed that by hiding the root BDS instead of destroying
> it.  Destruction only happens on unplug.  "Hiding" means removing it
> from bdrv_states and graph_bdrv_states; see bdrv_make_anon().
> 
> This "destroy on revoke" is a misfeature we don't want to carry
> forward to blockdev-add, just like "destroy on unplug" (commit
> 2d246f0).  So make drive_del fail on anything added with blockdev-add.
> 
> We'll add separate QMP commands to revoke device model access and to
> destroy backends.
> 
> Signed-off-by: Markus Armbruster <address@hidden>

Oops, was this still missing? I've been meaning to forbid this since we
introduced blockdev-add, but apparently never got around to doing it.

Thanks, applied to the block branch.

Kevin