Thanks Christoph.
Cached getlength with pread/pwrite:
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
96.97 1.760111 11893 148 4 futex
1.61 0.029209 1 46891 2217 select
0.28 0.005047 0 64609 timer_gettime
0.22 0.004059 0 42745 2578 rt_sigreturn
0.22 0.003911 0 46261 timer_settime
0.18 0.003280 1093 3 shmdt
0.17 0.003095 0 23859 pread <---
0.17 0.003061 0 42800 write
0.16 0.002916 0 47759 5151 read
0.02 0.000285 0 645 writev
[...]
0.00 0.000000 0 13 lseek
Note that this is a Tiny Core Linux boot from disk and shutdown; not
very I/O intensive since it only loads a kernel and ~10 MB initramfs
without touching the disk much after kernel load.
diff --git a/block.c b/block.c
index 0f6be17..5c1652c 100644
--- a/block.c
+++ b/block.c
@@ -363,6 +363,7 @@ static int bdrv_open_common(BlockDriverState *bs,
const char *filename,
assert(drv != NULL);
bs->file = NULL;
+ bs->total_sectors = 0;
bs->is_temporary = 0;
bs->encrypted = 0;
bs->valid_key = 0;
@@ -416,9 +417,7 @@ static int bdrv_open_common(BlockDriverState *bs,
const char *filename,
}
bs->keep_read_only = bs->read_only = !(open_flags & BDRV_O_RDWR);
- if (drv->bdrv_getlength) {
- bs->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
- }
+ bs->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
#ifndef _WIN32
if (bs->is_temporary) {
unlink(filename);
@@ -957,13 +956,26 @@ int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
int bdrv_truncate(BlockDriverState *bs, int64_t offset)
{
BlockDriver *drv = bs->drv;
+ int ret;
if (!drv)
return -ENOMEDIUM;
if (!drv->bdrv_truncate)
return -ENOTSUP;
if (bs->read_only)
return -EACCES;
- return drv->bdrv_truncate(bs, offset);
+ ret = drv->bdrv_truncate(bs, offset);
+ if (ret < 0) {
+ return ret;
+ }
+
+ /* refresh total sectors */
+ if (drv->bdrv_getlength) {
+ bs->total_sectors = 0; /* discard cached value */
+ bs->total_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS;
+ } else {
+ bs->total_sectors = offset >> BDRV_SECTOR_BITS;
+ }
+ return ret;
}
/**
@@ -974,8 +986,12 @@ int64_t bdrv_getlength(BlockDriverState *bs)
BlockDriver *drv = bs->drv;
if (!drv)
return -ENOMEDIUM;
- if (!drv->bdrv_getlength) {
- /* legacy mode */
+
+ /* Fixed size devices use the total_sectors value for speed instead of
+ issuing a length query (like lseek) on each call. Also, legacy block
+ drivers don't provide a bdrv_getlength function and must use
+ total_sectors. */
+ if ((bs->total_sectors && !bs->growable) || !drv->bdrv_getlength) {
return bs->total_sectors * BDRV_SECTOR_SIZE;
}
return drv->bdrv_getlength(bs);
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;
Stefan
