This patch is needed in order to build Guix on a Btrfs file system. From da922703282b0d3b8837a99a9c7fdd32f1d20d49 Mon Sep 17 00:00:00 2001 From: Mark H Weaver 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) 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: -- 2.15.1