Re: [Qemu-devel] [PATCH 0/2] introduce bdrv_swap, implement bdrv_append on top

[Paolo Bonzini <pbonzini@redhat.com>]

Il 15/06/2012 11:38, Kevin Wolf ha scritto:
>> > Yet another tiny bit extracted from block mirroring, looks like it
>> > should be useful for block commit too.
>> > 
>> > Paolo Bonzini (2):
>> >   block: copy over job and dirty bitmap fields in bdrv_append
>> >   block: introduce bdrv_swap, implement bdrv_append on top of it
>> > 
>> >  block.c |  175 +++++++++++++++++++++++++++++++++++++--------------------------
>> >  block.h |    1 +
>> >  2 files changed, 103 insertions(+), 73 deletions(-)
>> > 
> I was really hoping we could get rid of bdrv_append() rather than extend
> it and spread its use...
> 
> What exactly do we need this for? I'm sure you have good reasons, but
> with such hackish approaches the justification should be explicit.

It's part of the replacement for drive_reopen.  It is used by a new
command called block-job-complete when switching the device from the
mirroring source to the target.  Unlike drive_reopen, it is safe (it
just reuses the target BDS without closing it) and asynchronous, so
overall an improvement.

Paolo