The code is similar to the implementation of discard and write_zeroes
with UNMAP. There is no fallocate flag for this operation (yet?)
so we must write XFS-specific code like xfs_discard.
With an image stored on XFS, doing this in the guest:
# sg_write_same --in /dev/zero --num=256 --lba=0 /dev/sda
will give "qemu-img map" output similar to the following:
{ "start": 0, "length": 131072, "depth": 0, "zero": true, "data": true,
"offset": 0}
where the unwritten extents are exposed as a preallocated zero area.
The stale page cache problem can be reproduced as follows:
# modprobe scsi-debug lbpws=1 lbprz=1
# ./qemu-io /dev/sdXX
qemu-io> write -P 0xcc 0 2M
qemu-io> write -z 0 1M
qemu-io> read -P 0x00 0 512
Pattern verification failed at offset 0, 512 bytes
qemu-io> read -v 0 512
00000000: cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc ................
...
# ./qemu-io --cache=none /dev/sdXX
qemu-io> write -P 0xcc 0 2M
qemu-io> write -z 0 1M
qemu-io> read -P 0x00 0 512
qemu-io> read -v 0 512
00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
...
And similarly with discard instead of "write -z".
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
block/raw-aio.h | 3 +-
block/raw-posix.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++---------
2 files changed, 75 insertions(+), 15 deletions(-)
diff --git a/block/raw-aio.h b/block/raw-aio.h
index c61f159..7ad0a8a 100644
--- a/block/raw-aio.h
+++ b/block/raw-aio.h
@@ -21,9 +21,10 @@
#define QEMU_AIO_IOCTL 0x0004
#define QEMU_AIO_FLUSH 0x0008
#define QEMU_AIO_DISCARD 0x0010
+#define QEMU_AIO_WRITE_ZEROES 0x0020
#define QEMU_AIO_TYPE_MASK \
(QEMU_AIO_READ|QEMU_AIO_WRITE|QEMU_AIO_IOCTL|QEMU_AIO_FLUSH| \
- QEMU_AIO_DISCARD)
+ QEMU_AIO_DISCARD|QEMU_AIO_WRITE_ZEROES)
/* AIO flags */
#define QEMU_AIO_MISALIGNED 0x1000
diff --git a/block/raw-posix.c b/block/raw-posix.c
index 5cb46f1..6515def 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -142,6 +142,7 @@ typedef struct BDRVRawState {
bool is_xfs : 1;
#endif
bool has_discard : 1;
+ bool has_write_zeroes : 1;
bool discard_zeroes : 1;
} BDRVRawState;
@@ -327,6 +328,7 @@ static int raw_open_common(BlockDriverState *bs, QDict
*options,
#endif
s->has_discard = true;
+ s->has_write_zeroes = true;
if (fstat(s->fd, &st) < 0) {
error_setg_errno(errp, errno, "Could not stat file");
@@ -335,20 +337,21 @@ static int raw_open_common(BlockDriverState *bs, QDict
*options,
if (S_ISREG(st.st_mode)) {
s->discard_zeroes = true;
}
-#ifdef BLKDISCARDZEROES
if (S_ISBLK(st.st_mode)) {
+#ifdef BLKDISCARDZEROES
unsigned int arg;
if (ioctl(s->fd, BLKDISCARDZEROES, &arg) == 0 && arg) {
s->discard_zeroes = true;
}
- }
#endif
#ifdef CONFIG_LINUX
/* On Linux 3.10, BLKDISCARD leaves stale data in the page cache. Do
* not rely on the contents of discarded blocks unless using O_DIRECT.
+ * Same for BLKZEROOUT.
*/
if (!(bs->open_flags & BDRV_O_NOCACHE)) {
s->discard_zeroes = false;
+ s->has_write_zeroes = false;
}
#endif
}
@@ -704,6 +707,23 @@ static ssize_t handle_aiocb_rw(RawPosixAIOData *aiocb)
}
#ifdef CONFIG_XFS
+static int xfs_write_zeroes(BDRVRawState *s, int64_t offset, uint64_t bytes)
+{
+ struct xfs_flock64 fl;
+
+ memset(&fl, 0, sizeof(fl));
+ fl.l_whence = SEEK_SET;
+ fl.l_start = offset;
+ fl.l_len = bytes;
+
+ if (xfsctl(NULL, s->fd, XFS_IOC_ZERO_RANGE, &fl) < 0) {
+ DEBUG_BLOCK_PRINT("cannot write zero range (%s)\n", strerror(errno));
+ return -errno;
+ }
+
+ return 0;
+}
+
static int xfs_discard(BDRVRawState *s, int64_t offset, uint64_t bytes)
{
struct xfs_flock64 fl;
@@ -722,6 +742,42 @@ static int xfs_discard(BDRVRawState *s, int64_t offset,
uint64_t bytes)
}
#endif
+static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb)
+{
+ int ret = -EOPNOTSUPP;
+ BDRVRawState *s = aiocb->bs->opaque;
+
+ if (s->has_write_zeroes == 0) {
+ return -ENOTSUP;
+ }
+
+ if (aiocb->aio_type & QEMU_AIO_BLKDEV) {
+#ifdef BLKZEROOUT
+ do {
+ uint64_t range[2] = { aiocb->aio_offset, aiocb->aio_nbytes };
+ if (ioctl(aiocb->aio_fildes, BLKZEROOUT, range) == 0) {
+ return 0;
+ }
+ } while (errno == EINTR);
+
+ ret = -errno;
+#endif
+ } else {
+#ifdef CONFIG_XFS
+ if (s->is_xfs) {
+ return xfs_write_zeroes(s, aiocb->aio_offset, aiocb->aio_nbytes);
+ }
+#endif
+ }
+
+ if (ret == -ENODEV || ret == -ENOSYS || ret == -EOPNOTSUPP ||
+ ret == -ENOTTY) {
+ s->has_write_zeroes = false;
+ ret = -ENOTSUP;
+ }
+ return ret;
+}
+
static ssize_t handle_aiocb_discard(RawPosixAIOData *aiocb)
{
int ret = -EOPNOTSUPP;
@@ -806,6 +862,9 @@ static int aio_worker(void *arg)
case QEMU_AIO_DISCARD:
ret = handle_aiocb_discard(aiocb);
break;
+ case QEMU_AIO_WRITE_ZEROES:
+ ret = handle_aiocb_write_zeroes(aiocb);
+ break;
default:
fprintf(stderr, "invalid aio request (0x%x)\n", aiocb->aio_type);
ret = -EINVAL;
@@ -1258,13 +1317,13 @@ static int coroutine_fn raw_co_write_zeroes(
BDRVRawState *s = bs->opaque;
if (!(flags & BDRV_REQ_MAY_UNMAP)) {
- return -ENOTSUP;
- }
- if (!s->discard_zeroes) {
- return -ENOTSUP;
+ return paio_submit_co(bs, s->fd, sector_num, NULL, nb_sectors,
+ QEMU_AIO_WRITE_ZEROES);
+ } else if (s->discard_zeroes) {
+ return paio_submit_co(bs, s->fd, sector_num, NULL, nb_sectors,
+ QEMU_AIO_DISCARD);
}
- return paio_submit_co(bs, s->fd, sector_num, NULL, nb_sectors,
- QEMU_AIO_DISCARD);
+ return -ENOTSUP;
}
static int raw_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
@@ -1615,13 +1674,13 @@ static coroutine_fn int
hdev_co_write_zeroes(BlockDriverState *bs,
return rc;
}
if (!(flags & BDRV_REQ_MAY_UNMAP)) {
- return -ENOTSUP;
- }
- if (!s->discard_zeroes) {
- return -ENOTSUP;
+ return paio_submit_co(bs, s->fd, sector_num, NULL, nb_sectors,
+ QEMU_AIO_WRITE_ZEROES|QEMU_AIO_BLKDEV);
+ } else if (s->discard_zeroes) {
+ return paio_submit_co(bs, s->fd, sector_num, NULL, nb_sectors,
+ QEMU_AIO_DISCARD|QEMU_AIO_BLKDEV);
}
- return paio_submit_co(bs, s->fd, sector_num, NULL, nb_sectors,
- QEMU_AIO_DISCARD|QEMU_AIO_BLKDEV);
+ return -ENOTSUP;
}
static int hdev_create(const char *filename, QEMUOptionParameter *options,
--
1.8.4.2
