linux-ext4 - [PATCH] libext2fs: have UNIX IO manager use pread64/pwrite64

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Date:	Fri,  8 Aug 2014 17:01:03 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Theodore Ts'o <tytso@....edu>
Subject: [PATCH] libext2fs: have UNIX IO manager use pread64/pwrite64

Commit baa3544609da3c ("libext2fs: have UNIX IO manager use
pread/pwrite) causes a breakage on 32-bit systems where off_t is
32-bits for file systems larger than 4GB.  Fix this by using
pread64/pwrite64 if possible, and if pread64/pwrite64 is not present,
using pread/pwrite only if the size of off_t is at least as big as
ext2_loff_t.

Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 configure            |  2 +-
 configure.in         |  2 ++
 lib/config.h.in      |  6 ++++++
 lib/ext2fs/unix_io.c | 24 ++++++++++++++++++++++--
 4 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/configure b/configure
index f0af1d5..b9ce43d 100755
--- a/configure
+++ b/configure
@@ -12994,7 +12994,7 @@ if test "$ac_res" != no; then :
 fi
 
 fi
-for ac_func in  	__secure_getenv 	backtrace 	blkid_probe_get_topology 	blkid_probe_enable_partitions 	chflags 	fadvise64 	fallocate 	fallocate64 	fchown 	fdatasync 	fstat64 	ftruncate64 	futimes 	getcwd 	getdtablesize 	getmntinfo 	getpwuid_r 	getrlimit 	getrusage 	jrand48 	llseek 	lseek64 	mallinfo 	mbstowcs 	memalign 	mempcpy 	mmap 	msync 	nanosleep 	open64 	pathconf 	posix_fadvise 	posix_fadvise64 	posix_memalign 	prctl 	pread 	pwrite 	secure_getenv 	setmntent 	setresgid 	setresuid 	snprintf 	srandom 	stpcpy 	strcasecmp 	strdup 	strnlen 	strptime 	strtoull 	sync_file_range 	sysconf 	usleep 	utime 	valloc
+for ac_func in  	__secure_getenv 	backtrace 	blkid_probe_get_topology 	blkid_probe_enable_partitions 	chflags 	fadvise64 	fallocate 	fallocate64 	fchown 	fdatasync 	fstat64 	ftruncate64 	futimes 	getcwd 	getdtablesize 	getmntinfo 	getpwuid_r 	getrlimit 	getrusage 	jrand48 	llseek 	lseek64 	mallinfo 	mbstowcs 	memalign 	mempcpy 	mmap 	msync 	nanosleep 	open64 	pathconf 	posix_fadvise 	posix_fadvise64 	posix_memalign 	prctl 	pread 	pwrite 	pread64 	pwrite64 	secure_getenv 	setmntent 	setresgid 	setresuid 	snprintf 	srandom 	stpcpy 	strcasecmp 	strdup 	strnlen 	strptime 	strtoull 	sync_file_range 	sysconf 	usleep 	utime 	valloc
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
diff --git a/configure.in b/configure.in
index b825f3d..2e59fde 100644
--- a/configure.in
+++ b/configure.in
@@ -1061,6 +1061,8 @@ AC_CHECK_FUNCS(m4_flatten([
 	prctl
 	pread
 	pwrite
+	pread64
+	pwrite64
 	secure_getenv
 	setmntent
 	setresgid
diff --git a/lib/config.h.in b/lib/config.h.in
index 34fb0cc..50cf312 100644
--- a/lib/config.h.in
+++ b/lib/config.h.in
@@ -328,6 +328,9 @@
 /* Define to 1 if you have the `pread' function. */
 #undef HAVE_PREAD
 
+/* Define to 1 if you have the `pread64' function. */
+#undef HAVE_PREAD64
+
 /* Define if the <pthread.h> defines PTHREAD_MUTEX_RECURSIVE. */
 #undef HAVE_PTHREAD_MUTEX_RECURSIVE
 
@@ -340,6 +343,9 @@
 /* Define to 1 if you have the `pwrite' function. */
 #undef HAVE_PWRITE
 
+/* Define to 1 if you have the `pwrite64' function. */
+#undef HAVE_PWRITE64
+
 /* Define to 1 if dirent has d_reclen */
 #undef HAVE_RECLEN_DIRENT
 
diff --git a/lib/ext2fs/unix_io.c b/lib/ext2fs/unix_io.c
index 0dd1490..eb39b28 100644
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -131,11 +131,21 @@ static errcode_t raw_read_blk(io_channel channel,
 	data->io_stats.bytes_read += size;
 	location = ((ext2_loff_t) block * channel->block_size) + data->offset;
 
-#ifdef HAVE_PREAD
+#ifdef HAVE_PREAD64
 	/* Try an aligned pread */
 	if ((channel->align == 0) ||
 	    (IS_ALIGNED(buf, channel->align) &&
 	     IS_ALIGNED(size, channel->align))) {
+		actual = pread64(data->dev, buf, size, location);
+		if (actual == size)
+			return 0;
+	}
+#elif HAVE_PREAD
+	/* Try an aligned pread */
+	if ((sizeof(off_t) >= sizeof(ext2_loff_t)) &&
+	    ((channel->align == 0) ||
+	     (IS_ALIGNED(buf, channel->align) &&
+	      IS_ALIGNED(size, channel->align)))) {
 		actual = pread(data->dev, buf, size, location);
 		if (actual == size)
 			return 0;
@@ -213,11 +223,21 @@ static errcode_t raw_write_blk(io_channel channel,
 
 	location = ((ext2_loff_t) block * channel->block_size) + data->offset;
 
-#ifdef HAVE_PWRITE
+#ifdef HAVE_PWRITE64
 	/* Try an aligned pwrite */
 	if ((channel->align == 0) ||
 	    (IS_ALIGNED(buf, channel->align) &&
 	     IS_ALIGNED(size, channel->align))) {
+		actual = pwrite64(data->dev, buf, size, location);
+		if (actual == size)
+			return 0;
+	}
+#elif HAVE_PWRITE
+	/* Try an aligned pwrite */
+	if ((sizeof(off_t) >= sizeof(ext2_loff_t)) &&
+	    ((channel->align == 0) ||
+	     (IS_ALIGNED(buf, channel->align) &&
+	      IS_ALIGNED(size, channel->align)))) {
 		actual = pwrite(data->dev, buf, size, location);
 		if (actual == size)
 			return 0;
-- 
2.0.0

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