Re: [f2fs-dev] [PATCH 1/2] f2fs-tools: use pread and pwrite when they are available.

[Sheng Yong via Linux-f2fs-devel]

On 2024/12/10 16:28, LongPing Wei wrote:

This patch want to reduce the number of system calls to improve performance.
pread and pwrite will only be used when the target platform support them.

Signed-off-by: LongPing Wei <weilongp...@oppo.com>
---
  configure.ac     |  4 +++-
  lib/libf2fs_io.c | 29 +++++++++++++++++++++++++++++
  2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 2053a65..439b97f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -182,6 +182,7 @@ AC_TYPE_SIZE_T
  AC_FUNC_GETMNTENT
  AC_CHECK_FUNCS_ONCE([
        add_key
+       clock_gettime
        fallocate
        fsetxattr
        fstat
@@ -193,7 +194,8 @@ AC_CHECK_FUNCS_ONCE([
        keyctl
        memset
        setmntent
-       clock_gettime
+       pread
+       pwrite
  ])

AS_IF([test "$ac_cv_header_byteswap_h" = "yes"],

diff --git a/lib/libf2fs_io.c b/lib/libf2fs_io.c
index 520ae03..a8430c9 100644
--- a/lib/libf2fs_io.c
+++ b/lib/libf2fs_io.c
@@ -279,6 +279,12 @@ static int dcache_io_read(long entry, __u64 offset, off_t 
blk)
        if (fd < 0)
                return fd;

+#ifdef HAVE_PREAD

+       if (pread(fd, dcache_buf + entry * F2FS_BLKSIZE, F2FS_BLKSIZE, offset) 
< 0) {
+               MSG(0, "\n pread() fail.\n");
+               return -1;
+       }
+#else
        if (lseek(fd, offset, SEEK_SET) < 0) {
                MSG(0, "\n lseek fail.\n");
                return -1;
@@ -287,6 +293,7 @@ static int dcache_io_read(long entry, __u64 offset, off_t 
blk)
                MSG(0, "\n read() fail.\n");
                return -1;
        }
+#endif
        dcache_lastused[entry] = ++dcache_usetick;
        dcache_valid[entry] = true;
        dcache_blk[entry] = blk;
@@ -393,10 +400,15 @@ int dev_read_version(void *buf, __u64 offset, size_t len)
  {
        if (c.sparse_mode)
                return 0;
+#ifdef HAVE_RPEAD
+       if (pread(c.kd, buf, len, (off_t)offset) < 0)
+               return -1;
+#else
        if (lseek(c.kd, (off_t)offset, SEEK_SET) < 0)
                return -1;
        if (read(c.kd, buf, len) < 0)
                return -1;
+#endif
        return 0;
  }

@@ -535,10 +547,15 @@ int dev_read(void *buf, __u64 offset, size_t len)

        fd = __get_device_fd(&offset);
        if (fd < 0)
                return fd;
+#ifdef HAVE_PREAD
+       if (pread(fd, buf, len, (off_t)offset) < 0)
+               return -1;
+#else
        if (lseek(fd, (off_t)offset, SEEK_SET) < 0)
                return -1;
        if (read(fd, buf, len) < 0)
                return -1;
+#endif
        return 0;
  }

@@ -615,8 +632,10 @@ static int __dev_write(void *buf, __u64 offset, size_t len, enum rw_hint whint)

        if (fd < 0)
                return fd;

+#ifndef HAVE_PWRITE

        if (lseek(fd, (off_t)offset, SEEK_SET) < 0)
                return -1;
+#endif

Hi, LongPing,

Can we move lseek and the following write together after writehint
operation? I think there is no need to place writehint between lseek
and write, because writehint affects the inode and does not affects
the pos in struct file.

However, I am wondering if writehint here works as expected when fd
is not opened with O_SYNC or O_DSYN, especially if multiple writes
occur in a short period of time. Please correct me if I miss something.

thanks,
shengyong

#if ! defined(__MINGW32__)

        if (c.need_whint && (c.whint != whint)) {
@@ -629,8 +648,13 @@ static int __dev_write(void *buf, __u64 offset, size_t 
len, enum rw_hint whint)
        }
  #endif

+#ifdef HAVE_PWRITE

+       if (pwrite(fd, buf, len, (off_t)offset) < 0)
+               return -1;
+#else
        if (write(fd, buf, len) < 0)
                return -1;
+#endif

c.need_fsync = true; @@ -663,10 +687,15 @@ int dev_write_block(void *buf, __u64 blk_addr, enum rw_hint whint) int dev_write_dump(void *buf, __u64 offset, size_t len)

  {
+#ifdef HAVE_PWRITE
+       if (pwrite(c.dump_fd, buf, len, (off_t)offset) < 0)
+               return -1;
+#else
        if (lseek(c.dump_fd, (off_t)offset, SEEK_SET) < 0)
                return -1;
        if (write(c.dump_fd, buf, len) < 0)
                return -1;
+#endif
        return 0;
  }

_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel