Commit 4899d10d authored by Stefan Hajnoczi's avatar Stefan Hajnoczi Committed by Kevin Wolf
Browse files

raw-posix: Use pread/pwrite instead of lseek+read/write 



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 <jan.kiszka@siemens.com> for identifying excessive
lseek and Christoph Hellwig <hch@lst.de> for confirming that this
approach should work.

Signed-off-by: default avatarStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent 508e0893

block/raw-posix.c

+4 −33
Original line number Diff line number Diff line
@@ -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;