On Mon, Mar 21 2016 at 3:11pm -0400, Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > On Mon, Mar 21, 2016 at 02:52:00PM -0400, Mike Snitzer wrote: > > On Tue, Mar 15, 2016 at 3:42 PM, Darrick J. Wong > > <darrick.wong@xxxxxxxxxx> wrote: > > > After much discussion, it seems that the fallocate feature flag > > > FALLOC_FL_ZERO_RANGE maps nicely to SCSI WRITE SAME; and the feature > > > FALLOC_FL_PUNCH_HOLE maps nicely to the devices that have been > > > whitelisted for zeroing SCSI UNMAP. Punch still requires that > > > FALLOC_FL_KEEP_SIZE is set. A length that goes past the end of the > > > device will be clamped to the device size if KEEP_SIZE is set; or will > > > return -EINVAL if not. Both start and length must be aligned to the > > > device's logical block size. > > > > > > Since the semantics of fallocate are fairly well established already, > > > wire up the two pieces. The other fallocate variants (collapse range, > > > insert range, and allocate blocks) are not supported. > > > > I'd like to see fallocate (block allocation) extend down to DM thinp. > > This more traditional use of fallocate would be useful for ensuring > > ENOSPC won't occur -- especially important if the FS has committed > > space in response to fallocate. As of now fallocate doesn't inform DM > > thinp at all. Curious why you decided not to wire it up? > > I don't know what to wire it up to. :) Fair enough. Yes something needs to be invented. > I didn't find any blkdev_* function that looked encouraging, though I > haven't dug too deeply into bfoster's "prototype a block reservation > allocation model" patchset yet. At a high level I'd guess that would > be a reasonable piece to connect to? It looks like the piece I want > is blk_provision_space(). Yes, something like that. > > But I'm not sure what "it" (the "allocate blocks" variant) even is > > given falloc.h doesn't show anything like "_ALLOCATE_BLOCKS"... > > The default behavior of fallocate is to allocate blocks, which means > that one invokes it by not passing any mode flags (except possibly > KEEP_SIZE). OK. > > It would require a new block interface to pass the fallocate extent > > down. But it seems bizarre to implement "some of" fallocate but not > > the most widely used case for fallocate. > > Agreed. I'd like to get the existing functionality wired up sooner than > later, and plumbing "allocate blocks" down to thinp can be done as a > followup. > > (Or stall long enough that it becomes one patchset.) Sure, sounds good. Glad we're in agreement. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
