On Wednesday, January 10, 2018 3:42:52 AM CET Mark H Weaver wrote: > From da922703282b0d3b8837a99a9c7fdd32f1d20d49 Mon Sep 17 00:00:00 2001 > From: Mark H Weaver <m...@netris.org> > Date: Tue, 9 Jan 2018 20:16:14 -0500 > Subject: [PATCH] Remove nonportable check for files containing only zeroes. > > This check benefitted only one unlikely case (large files containing > only zeroes, on systems that do not support SEEK_HOLE)
It drops the optimization even for situations when SEEK_HOLE is not available, which is not 100% necessary. I'm not proposing doing otherwise (I actually proposed this in [1]), but I'm rather CCing Andreas once more, as that's the original requester, the use-cases with lustre were definitely not unlikely and the question is whether SEEK_HOLE covers them nowadays. [1] https://lists.gnu.org/archive/html/bug-tar/2016-07/msg00017.html Pavel > and was based on an assumption about file system behavior that is not > mandated by POSIX and no longer holds in practice, namely that for > sufficiently large files, (st_blocks == 0) implies that the file > contains only zeroes. Examples of file systems that violate this > assumption include Linux's /proc file system and Btrfs. > > * src/sparse.c (sparse_scan_file_wholesparse): Remove this function. > (sparse_scan_file_seek): Remove the initial check for files containing > only zeroes. > --- > src/sparse.c | 24 ------------------------ > 1 file changed, 24 deletions(-) > > diff --git a/src/sparse.c b/src/sparse.c > index d41c0ea..3de6560 100644 > --- a/src/sparse.c > +++ b/src/sparse.c > @@ -261,26 +261,6 @@ sparse_scan_file_raw (struct tar_sparse_file *file) > return tar_sparse_scan (file, scan_end, NULL); > } > > -static bool > -sparse_scan_file_wholesparse (struct tar_sparse_file *file) > -{ > - struct tar_stat_info *st = file->stat_info; > - struct sp_array sp = {0, 0}; > - > - /* Note that this function is called only for truly sparse files of size > >= 1 > - block size (checked via ST_IS_SPARSE before). See the thread > - http://www.mail-archive.com/bug-tar@gnu.org/msg04209.html for more info > */ > - if (ST_NBLOCKS (st->stat) == 0) > - { > - st->archive_file_size = 0; > - sp.offset = st->stat.st_size; > - sparse_add_map (st, &sp); > - return true; > - } > - > - return false; > -} > - > #ifdef SEEK_HOLE > /* Try to engage SEEK_HOLE/SEEK_DATA feature. */ > static bool > @@ -343,10 +323,6 @@ sparse_scan_file_seek (struct tar_sparse_file *file) > static bool > sparse_scan_file (struct tar_sparse_file *file) > { > - /* always check for completely sparse files */ > - if (sparse_scan_file_wholesparse (file)) > - return true; > - > switch (hole_detection) > { > case HOLE_DETECTION_DEFAULT: >