On Wed, Jul 18, 2018 at 01:27:40PM -0700, Eric Sandeen wrote: > > > On 7/18/18 12:59 PM, Darrick J. Wong wrote: > > On Wed, Jul 18, 2018 at 12:41:27PM -0600, Chris Murphy wrote: > >> xfsprogs 4.17.0 mkfs with reflink=1 > >> kernel 4.17.6 > >> > >> $ fallocate -l 1g tmp2 > >> $ cp --reflink tmp2 tmp3 > >> $ filefrag -v * > >> Filesystem type is: 58465342 > >> File size of tmp2 is 1073741824 (262144 blocks of 4096 bytes) > >> ext: logical_offset: physical_offset: length: expected: flags: > >> 0: 0.. 130136: 24.. 130160: 130137: unwritten > >> 1: 130137.. 260280: 131082.. 261225: 130144: 130161: unwritten > >> 2: 260281.. 262143: 264714.. 266576: 1863: 261226: > >> last,unwritten,eof > >> tmp2: 3 extents found > >> File size of tmp3 is 1073741824 (262144 blocks of 4096 bytes) > >> tmp3: 0 extents found > >> [chris@f28s xfs]$ > >> > >> > >> Is this expected? When I do it on Btrfs, I see identical information > >> for the two files after reflink copy, with flags "unwritten,shared". > > > > Yes. xfs doesn't share unwritten extents; what would be the point? > > > > --D > > <materializes somewhere on a US western interstate> > > Seems a little weird that bare cp will create a written file full of > zeros, while a cp --reflink will create a sparse file, though? cp actually can have different behaviors when --reflink is specified, from the manpage (formatting slightly modified): " By default, sparse SOURCE files are detected by a crude heuristic and the corresponding DEST file is made sparse as well. That is the behavior selected by --sparse=auto. Specify --sparse=always to create a sparse DEST file whenever the SOURCE file contains a long enough sequence of zero bytes. Use --sparse=never to inhibit creation of sparse files. When --reflink[=always] is specified, perform a lightweight copy, where the data blocks are copied only when modified. If this is not possible the copy fails, or if --reflink=auto is specified, fall back to a standard copy. " > > -Eric > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Carlos -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
