Use SEEK_HOLE for hole detection

Based on patch by Pavel Raiskup.

Use SEEK_HOLE/SEEK_DATA feature of lseek on systems that support
it.  This can make archiving of sparse files much faster.

Implement the --hole-detection option to allow users to select
hole-detection method.

* src/common.h (hole_detection_method): New enum.
(hole_detection): New global.
* src/sparse.c  (sparse_scan_file_wholesparse): New function as a
method for detecting sparse files without any data.
(sparse_scan_file_raw): Rename from sparse_scan_file; with edits.
(sparse_scan_file_seek): New function.
(sparse_scan_file): Reimplement function.
* src/tar.c: New option --hole-detection

* tests/checkseekhole.c: New file.
* tests/.gitignore: Mention two test binaries.
* tests/Makefile.am: Add new tests.
* tests/testsuite.at (AT_SEEKHOLE_PREREQ): New macro.
Include sparse06.at.
* tests/sparse06.at: New test case.
* tests/sparse02.at: Force raw hole-detection method.
* tests/sparsemv.at: Likewise.
* tests/sparsemvp.at: Likewise.

* doc/tar.1: Document --hole-detection option.
* doc/tar.texi: Document hole-detection algorithms and
command-line options.
* NEWS: Document hole-detection.

tests/.gitignore

@@ -9,3 +9,5 @@ argcv.h
 genfile.c
 genfile
 download
+ttyemu
+checkseekhole

tests/Makefile.am

@@ -207,6 +207,7 @@ TESTSUITE_AT = \
  sparse03.at\
  sparse04.at\
  sparse05.at\
+ sparse06.at\
  sparsemv.at\
  sparsemvp.at\
  spmvp00.at\
@@ -275,13 +276,14 @@ installcheck-local: $(check_PROGRAMS)
 ## genfile      ##
 ## ------------ ##
 
-check_PROGRAMS = genfile
+check_PROGRAMS = genfile checkseekhole
 
 if TAR_COND_GRANTPT
 check_PROGRAMS += ttyemu
 endif
 
 genfile_SOURCES = genfile.c argcv.c argcv.h
+checkseekhole_SOURCES = checkseekhole.c
 
 ttyemu_SOURCES = ttyemu.c
 

tests/checkseekhole.c

@@ -0,0 +1,92 @@
+/* Test suite for GNU tar - SEEK_HOLE detector.
+
+   Copyright 2015 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by the
+   Free Software Foundation; either version 3, or (at your option) any later
+   version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General
+   Public License for more details.
+
+   You should have received a copy of the GNU General Public License along
+   with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+   Description:  detect whether it is possible to work with SEEK_HOLE on
+   particular operating system and file system. */
+
+#include "config.h"
+
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <fcntl.h>
+
+enum {
+    EX_OK = 0,    /* SEEK_HOLE support */
+    EX_FAIL,      /* test failed - no SEEK_HOLE support */
+    EX_BAD,       /* test is not relevant */
+};
+
+int
+check_seek_hole (int fd)
+{
+#ifdef SEEK_HOLE
+  struct stat stat;
+  off_t offset;
+
+  /* hole of 100MB */
+  if (lseek (fd, 100*1024*1024, SEEK_END) < 0)
+    return EX_BAD;
+
+  /* piece of data */
+  if (write (fd, "data\n", 5) != 5)
+    return EX_BAD;
+
+  /* another hole */
+  if (lseek (fd, 100*1024*1024, SEEK_END) < 0)
+    return EX_BAD;
+
+  /* piece of data */
+  if (write (fd, "data\n", 5) != 5)
+    return EX_BAD;
+
+  if (fstat (fd, &stat))
+    return EX_BAD;
+
+  offset = lseek (fd, 0, SEEK_DATA);
+  if (offset == (off_t)-1)
+    return EX_FAIL;
+
+  offset = lseek (fd, offset, SEEK_HOLE);
+  if (offset == (off_t)-1 || offset == stat.st_size)
+    return EX_FAIL;
+
+  return EX_OK;
+#else
+  return EX_BAD;
+#endif
+}
+
+int
+main ()
+{
+#ifdef SEEK_HOLE
+  int rc;
+  char template[] = "testseekhole-XXXXXX";
+  int fd = mkstemp (template);
+  if (fd == -1)
+    return EX_BAD;
+  rc = check_seek_hole (fd);
+  close (fd);
+  unlink (template);
+
+  return rc;
+#else
+  return EX_FAIL;
+#endif
+}

tests/sparse02.at

@@ -27,7 +27,7 @@ AT_KEYWORDS([sparse sparse02])
 
 AT_TAR_CHECK([
 genfile --sparse --file sparsefile --block-size 512 0 ABCD 1M EFGH 2000K IJKL || AT_SKIP_TEST
-tar -c -f archive --sparse sparsefile || exit 1
+tar --hole-detection=raw -c -f archive --sparse sparsefile || exit 1
 echo separator
 
 tar xfO archive | cat - > sparsecopy || exit 1

tests/sparse06.at

@@ -0,0 +1,56 @@
+# Process this file with autom4te to create testsuite. -*- Autotest -*-
+#
+# Test suite for GNU tar.
+# Copyright 2014 Free Software Foundation, Inc.
+
+# This file is part of GNU tar.
+
+# GNU tar is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+
+# GNU tar is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+AT_SETUP([storing sparse file using seek method])
+AT_KEYWORDS([sparse sparse06])
+
+m4_define([check_pattern],[
+rm -rf out archive.tar smallsparse && mkdir out
+genfile --sparse --file smallsparse $1
+tar -cSf archive.tar smallsparse
+tar -xf archive.tar -C out
+cmp smallsparse out/smallsparse
+])
+
+AT_TAR_CHECK([
+AT_SEEKHOLE_PREREQ
+AT_TIMEOUT_PREREQ
+
+TAR_OPTIONS="$TAR_OPTIONS --hole-detection=seek"
+genfile --sparse --file bigsparse 0 ABC 8G DEF
+timeout 2 tar -cSf a bigsparse
+test $? -eq 0 || exit 1
+
+check_pattern([0 ABC])
+check_pattern([0 ABC 10M])
+check_pattern([0 ABC 10M DEF])
+
+check_pattern([10M])
+check_pattern([10M ABC])
+check_pattern([10M ABC 20M])
+
+check_pattern([10M DEF 20M GHI 30M JKL 40M])
+
+],
+[0],,
+[genfile: created file is not sparse
+],,,[posix])
+
+AT_CLEANUP

tests/sparsemv.at

@@ -30,6 +30,7 @@ AT_KEYWORDS([sparse multiv sparsemv])
 
 AT_TAR_CHECK([
 exec <&-
+TAR_OPTIONS="$TAR_OPTIONS --hole-detection=raw"
 genfile --sparse --file sparsefile 0 ABCDEFGHIJK 1M ABCDEFGHI || AT_SKIP_TEST
 echo "Pass 1: Split between data blocks"
 echo "Create archive"

tests/sparsemvp.at

@@ -26,6 +26,7 @@ dnl TAR_MVP_TEST version map1 map2
 m4_define([TAR_MVP_TEST],[
 AT_TAR_CHECK([
 exec <&-
+TAR_OPTIONS="$TAR_OPTIONS --hole-detection=raw"
 genfile --sparse --file sparsefile $2 || AT_SKIP_TEST
 echo "Pass 1: Split between data blocks"
 echo "Create archive"

tests/testsuite.at

@@ -112,6 +112,19 @@ rm -f $[]$
 test $result -eq 0 || AT_SKIP_TEST
 ])
 
+dnl AT_SEEKHOLE_PREREQ
+m4_define([AT_SEEKHOLE_PREREQ],[
+checkseekhole || AT_SKIP_TEST
+])
+
+m4_define([AT_TIMEOUT_PREREQ],[
+timeout 100 true
+if test $? -ne 0; then
+    echo >&2 "the 'timeout' utility not found"
+    AT_SKIP_TEST
+fi
+])
+
 m4_define([AT_TAR_MKHIER],[
 install-sh -d $1 >/dev/null dnl
 m4_if([$2],,,&& genfile --file [$1]/[$2]) || AT_SKIP_TEST])
@@ -358,6 +371,7 @@ m4_include([sparse02.at])
 m4_include([sparse03.at])
 m4_include([sparse04.at])
 m4_include([sparse05.at])
+m4_include([sparse06.at])
 m4_include([sparsemv.at])
 m4_include([spmvp00.at])
 m4_include([spmvp01.at])