On Tue, 05/05 13:48, Kevin Wolf wrote: > Am 05.05.2015 um 12:27 hat Fam Zheng geschrieben: > > On Tue, 05/05 12:13, Paolo Bonzini wrote: > > > > > > > > > On 05/05/2015 09:36, Fam Zheng wrote: > > > I don't think this commit is relevant. The bug is caused by > > > bdrv_co_discard clearing the bitmap (which is not supported during > > > iteration, and is caught by the assertion). That bdrv_reset_dirty is > > > not removed by the commit you pointed out. > > > > You are right, I think the bug is the bdrv_reset_dirty in bdrv_co_discard. > > The > > discard may zero out the src area (depending on the backend), we should > > probably replicate this to dest (actual data or the discard operation), > > rather > > than forgetting the change. > > It depends. In its basic form, bdrv_discard() just means "I don't care > about the data any more". Then clearing the dirty bitmap is correct. > > The content is only important if the caller used discard to write zeros > because can_write_zeroes_with_unmap = true. Do we have any such callers > apart from qemu-img convert?
The guest could be taking advantage of this "can_write_zeroes_with_unmap".. Fam