At Tue, 25 Jun 2013 13:39:11 +0200, Kevin Wolf wrote: > > Hi all, > > while discussing some iscsi patches with Peter, we came to have a look > at which block drivers implement has_zero_init() to return 0, and which > don't (returning 1 is the default). > > The meaning of this value is that if has_zero_init != 0, after > bdrv_create() one can assume that the whole image would read back as all > zero. For example, this is true for the traditional image files, but not > for host_device, where the block device isn't really created during > bdrv_create() but only checked for size. > > The full list of protocol level block drivers is: > > * blkdebug - doesn't have bdrv_create > * blkverify - doesn't have bdrv_create > * curl - doesn't have bdrv_create > * gluster - currently has_zero_init = 1 (is this correct?) > * iscsi - has_zero_init = 0 > * nbd - doesn't have bdrv_create > * file - has_zero_init = 1 > * host_* - has_zero_init = 0 > * rbd - currently has_zero_init = 1 (is this correct?) > * sheepdog - currently has_zero_init = 1 (is this correct?) > * ssh - currently has_zero_init = 1 (is this correct?) > * vvfat - doesn't have bdrv_create > > Can you please review for the gluster, rbd, sheepdog and ssh driver > whether it's safe to assume that the image reads back as zeros after > bdrv_create?
It's safe for Sheepdog. Sheepdog uses ftruncate or fallocate to create data blocks and it is guaranteed that the space will be initialized to zero. Thanks, Kazutaka
