From patchwork Mon Apr 19 12:34:11 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [1/2] raw-posix: Use pread/pwrite instead of lseek+read/write Date: Mon, 19 Apr 2010 02:34:11 -0000 From: Stefan Hajnoczi X-Patchwork-Id: 50463 Message-Id: <1271680452-24121-1-git-send-email-stefanha@linux.vnet.ibm.com> To: qemu-devel@nongnu.org Cc: Kevin Wolf , Jan Kiszka , Christoph Hellwig , Stefan Hajnoczi 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 for identifying excessive lseek and Christoph Hellwig for confirming that this approach should work. Signed-off-by: Stefan Hajnoczi --- 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;