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[Qemu-devel] [PATCH 1/2] raw-posix: Use pread/pwrite instead of lseek+re
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PATCH 1/2] raw-posix: Use pread/pwrite instead of lseek+read/write |
Date: |
Mon, 19 Apr 2010 13:34:11 +0100 |
This patch combines the lseek+read/write calls to use pread/pwrite
instead. This will result in fewer system calls and is already used by
AIO.
Thanks to Jan Kiszka <address@hidden> for identifying excessive
lseek and Christoph Hellwig <address@hidden> for confirming that this
approach should work.
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
block/raw-posix.c | 37 ++++---------------------------------
1 files changed, 4 insertions(+), 33 deletions(-)
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 598ea19..7541ed2 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -105,7 +105,6 @@
typedef struct BDRVRawState {
int fd;
int type;
- unsigned int lseek_err_cnt;
int open_flags;
#if defined(__linux__)
/* linux floppy specific */
@@ -134,8 +133,6 @@ static int raw_open_common(BlockDriverState *bs, const char
*filename,
BDRVRawState *s = bs->opaque;
int fd, ret;
- s->lseek_err_cnt = 0;
-
s->open_flags = open_flags | O_BINARY;
s->open_flags &= ~O_ACCMODE;
if (bdrv_flags & BDRV_O_RDWR) {
@@ -243,19 +240,7 @@ static int raw_pread_aligned(BlockDriverState *bs, int64_t
offset,
if (ret < 0)
return ret;
- if (offset >= 0 && lseek(s->fd, offset, SEEK_SET) == (off_t)-1) {
- ++(s->lseek_err_cnt);
- if(s->lseek_err_cnt <= 10) {
- DEBUG_BLOCK_PRINT("raw_pread(%d:%s, %" PRId64 ", %p, %d) [%" PRId64
- "] lseek failed : %d = %s\n",
- s->fd, bs->filename, offset, buf, count,
- bs->total_sectors, errno, strerror(errno));
- }
- return -1;
- }
- s->lseek_err_cnt=0;
-
- ret = read(s->fd, buf, count);
+ ret = pread(s->fd, buf, count, offset);
if (ret == count)
goto label__raw_read__success;
@@ -276,12 +261,10 @@ static int raw_pread_aligned(BlockDriverState *bs,
int64_t offset,
/* Try harder for CDrom. */
if (bs->type == BDRV_TYPE_CDROM) {
- lseek(s->fd, offset, SEEK_SET);
- ret = read(s->fd, buf, count);
+ ret = pread(s->fd, buf, count, offset);
if (ret == count)
goto label__raw_read__success;
- lseek(s->fd, offset, SEEK_SET);
- ret = read(s->fd, buf, count);
+ ret = pread(s->fd, buf, count, offset);
if (ret == count)
goto label__raw_read__success;
@@ -313,19 +296,7 @@ static int raw_pwrite_aligned(BlockDriverState *bs,
int64_t offset,
if (ret < 0)
return -errno;
- if (offset >= 0 && lseek(s->fd, offset, SEEK_SET) == (off_t)-1) {
- ++(s->lseek_err_cnt);
- if(s->lseek_err_cnt) {
- DEBUG_BLOCK_PRINT("raw_pwrite(%d:%s, %" PRId64 ", %p, %d) [%"
- PRId64 "] lseek failed : %d = %s\n",
- s->fd, bs->filename, offset, buf, count,
- bs->total_sectors, errno, strerror(errno));
- }
- return -EIO;
- }
- s->lseek_err_cnt = 0;
-
- ret = write(s->fd, buf, count);
+ ret = pwrite(s->fd, buf, count, offset);
if (ret == count)
goto label__raw_write__success;
--
1.7.0