[PATCH 21/37] libext2fs: have UNIX IO manager use pread/pwrite

Darrick J. Wong
2014-05-01T23:14:44Z

If pread/pwrite are present, have the UNIX IO manager use them for
aligned IOs (instead of the current seek -> read/write), thereby
saving us a (minor) amount of system call overhead.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
configure | 2 +-
configure.in | 2 ++
lib/config.h.in | 6 ++++++
lib/ext2fs/unix_io.c | 24 ++++++++++++++++++++++++
4 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index 6449f59..7b0a0d1 100755
--- a/configure
+++ b/configure
@@ -11155,7 +11155,7 @@ if test "$ac_res" != no; then :
fi

fi
-for ac_func in __secure_getenv backtrace blkid_probe_get_topology 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 secure_getenv setmntent setresgid setresuid 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 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 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 8a033b0..f28bd46 100644
--- a/configure.in
+++ b/configure.in
@@ -1135,6 +1135,8 @@ AC_CHECK_FUNCS(m4_flatten([
posix_fadvise64
posix_memalign
prctl
+ pread
+ pwrite
secure_getenv
setmntent
setresgid
diff --git a/lib/config.h.in b/lib/config.h.in
index 12ac1e0..e0384ee 100644
--- a/lib/config.h.in
+++ b/lib/config.h.in
@@ -311,9 +311,15 @@
/* Define to 1 if you have the `prctl' function. */
#undef HAVE_PRCTL

+/* Define to 1 if you have the `pread' function. */
+#undef HAVE_PREAD
+
/* Define to 1 if you have the `putenv' function. */
#undef HAVE_PUTENV

+/* Define to 1 if you have the `pwrite' function. */
+#undef HAVE_PWRITE
+
/* 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 c3185b6..a818c13 100644
--- a/lib/ext2fs/unix_io.c
+++ b/lib/ext2fs/unix_io.c
@@ -130,6 +130,18 @@ static errcode_t raw_read_blk(io_channel channel,
size = (count < 0) ? -count : count * channel->block_size;
data->io_stats.bytes_read += size;
location = ((ext2_loff_t) block * channel->block_size) + data->offset;
+
+#ifdef HAVE_PREAD
+ /* Try an aligned pread */
+ if ((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;
+ }
+#endif /* HAVE_PREAD */
+
if (ext2fs_llseek(data->dev, location, SEEK_SET) != location) {
retval = errno ? errno : EXT2_ET_LLSEEK_FAILED;
goto error_out;
@@ -200,6 +212,18 @@ static errcode_t raw_write_blk(io_channel channel,
data->io_stats.bytes_written += size;

location = ((ext2_loff_t) block * channel->block_size) + data->offset;
+
+#ifdef HAVE_PWRITE
+ /* Try an aligned pwrite */
+ if ((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;
+ }
+#endif /* HAVE_PWRITE */
+
if (ext2fs_llseek(data->dev, location, SEEK_SET) != location) {
retval = errno ? errno : EXT2_ET_LLSEEK_FAILED;
goto error_out;