* [Qemu-devel] [RFC PATCH 1/2] block: Add BDRV_BLOCK_EOF to bdrv_get_block_status()
2017-05-05 2:14 [Qemu-devel] [RFC PATCH 0/2] Enhance block status when crossing EOF Eric Blake
@ 2017-05-05 2:14 ` Eric Blake
2017-05-05 2:15 ` [Qemu-devel] [RFC PATCH 2/2] block: Exploit BDRV_BLOCK_EOF for larger zero blocks Eric Blake
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: Eric Blake @ 2017-05-05 2:14 UTC (permalink / raw)
To: qemu-devel; +Cc: qemu-block, kwolf, mreitz, Stefan Hajnoczi, Fam Zheng
Just as the block layer already sets BDRV_BLOCK_ALLOCATED as a
shortcut for subsequent operations, there are also some optimizations
that are made easier if we can quickly tell that *pnum will advance
us to the end of a file, via a new BDRV_BLOCK_EOF which gets set
by the block layer.
This just plumbs up the new bit; subsequent patches will make use
of it.
Signed-off-by: Eric Blake <eblake@redhat.com>
---
include/block/block.h | 2 ++
block/io.c | 15 +++++++++++----
2 files changed, 13 insertions(+), 4 deletions(-)
diff --git a/include/block/block.h b/include/block/block.h
index c8bec7d..6aff894 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -128,6 +128,7 @@ typedef struct HDGeometry {
* BDRV_BLOCK_OFFSET_VALID: an associated offset exists for accessing raw data
* BDRV_BLOCK_ALLOCATED: the content of the block is determined by this
* layer (short for DATA || ZERO), set by block layer
+ * BDRV_BLOCK_EOF: the returned pnum covers through end of file for this layer
*
* Internal flag:
* BDRV_BLOCK_RAW: used internally to indicate that the request was
@@ -156,6 +157,7 @@ typedef struct HDGeometry {
#define BDRV_BLOCK_OFFSET_VALID 0x04
#define BDRV_BLOCK_RAW 0x08
#define BDRV_BLOCK_ALLOCATED 0x10
+#define BDRV_BLOCK_EOF 0x20
#define BDRV_BLOCK_OFFSET_MASK BDRV_SECTOR_MASK
typedef QSIMPLEQ_HEAD(BlockReopenQueue, BlockReopenQueueEntry) BlockReopenQueue;
diff --git a/block/io.c b/block/io.c
index fdd7485..a7bc8bd 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1727,15 +1727,16 @@ typedef struct BdrvCoGetBlockStatusData {
* Drivers not implementing the functionality are assumed to not support
* backing files, hence all their sectors are reported as allocated.
*
- * If 'sector_num' is beyond the end of the disk image the return value is 0
- * and 'pnum' is set to 0.
+ * If 'sector_num' is beyond the end of the disk image the return value is
+ * BDRV_BLOCK_EOF and 'pnum' is set to 0.
*
* 'pnum' is set to the number of sectors (including and immediately following
* the specified sector) that are known to be in the same
* allocated/unallocated state.
*
* 'nb_sectors' is the max value 'pnum' should be set to. If nb_sectors goes
- * beyond the end of the disk image it will be clamped.
+ * beyond the end of the disk image it will be clamped; if 'pnum' is set to
+ * the end of the image, then the returned value will include BDRV_BLOCK_EOF.
*
* If returned value is positive and BDRV_BLOCK_OFFSET_VALID bit is set, 'file'
* points to the BDS which the sector range is allocated in.
@@ -1756,7 +1757,7 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
if (sector_num >= total_sectors) {
*pnum = 0;
- return 0;
+ return BDRV_BLOCK_EOF;
}
n = total_sectors - sector_num;
@@ -1767,6 +1768,9 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
if (!bs->drv->bdrv_co_get_block_status) {
*pnum = nb_sectors;
ret = BDRV_BLOCK_DATA | BDRV_BLOCK_ALLOCATED;
+ if (sector_num + nb_sectors == total_sectors) {
+ ret |= BDRV_BLOCK_EOF;
+ }
if (bs->drv->protocol_name) {
ret |= BDRV_BLOCK_OFFSET_VALID | (sector_num * BDRV_SECTOR_SIZE);
}
@@ -1830,6 +1834,9 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
out:
bdrv_dec_in_flight(bs);
+ if (ret >= 0 && sector_num + *pnum == total_sectors) {
+ ret |= BDRV_BLOCK_EOF;
+ }
return ret;
}
--
2.9.3
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [Qemu-devel] [RFC PATCH 2/2] block: Exploit BDRV_BLOCK_EOF for larger zero blocks
2017-05-05 2:14 [Qemu-devel] [RFC PATCH 0/2] Enhance block status when crossing EOF Eric Blake
2017-05-05 2:14 ` [Qemu-devel] [RFC PATCH 1/2] block: Add BDRV_BLOCK_EOF to bdrv_get_block_status() Eric Blake
@ 2017-05-05 2:15 ` Eric Blake
2017-05-15 12:54 ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
2017-05-15 12:54 ` [Qemu-devel] [Qemu-block] [RFC PATCH 0/2] Enhance block status when crossing EOF Stefan Hajnoczi
2017-06-27 8:24 ` [Qemu-devel] " Fam Zheng
3 siblings, 1 reply; 6+ messages in thread
From: Eric Blake @ 2017-05-05 2:15 UTC (permalink / raw)
To: qemu-devel; +Cc: qemu-block, kwolf, mreitz, Stefan Hajnoczi, Fam Zheng
When we have a BSD with unallocated clusters, but asking the status
of its underlying bs->file or backing layer encounters an end-of-file
condition, we know that the rest of the unallocated area will read as
zeroes. However, pre-patch, this required two separate calls to
bdrv_get_block_status(), as the first call stops at the point where
the underlying file ends. Thanks to BDRV_BLOCK_EOF, we can now widen
the results of the primary status if the secondary status already
includes BDRV_BLOCK_ZERO.
In turn, this fixes a TODO mentioned in iotest 154, where we can now
see that all sectors in a partial cluster at the end of a file read
as zero when coupling the shorter backing file's status along with our
knowledge that the remaining sectors came from an unallocated cluster.
Also, note that the loop in bdrv_co_get_block_status_above() had an
inefficent exit: in cases where the active layer sets BDRV_BLOCK_ZERO
but does NOT set BDRV_BLOCK_ALLOCATED (namely, where we know we read
zeroes merely because our unallocated clusters lie beyond the backing
file's shorter length), we still ended up probing the backing layer
even though we already had a good answer.
Signed-off-by: Eric Blake <eblake@redhat.com>
---
block/io.c | 27 ++++++++++++++++++++++-----
tests/qemu-iotests/154 | 4 ----
tests/qemu-iotests/154.out | 12 ++++++------
3 files changed, 28 insertions(+), 15 deletions(-)
diff --git a/block/io.c b/block/io.c
index a7bc8bd..0ec9c75 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1819,10 +1819,13 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs,
/* Ignore errors. This is just providing extra information, it
* is useful but not necessary.
*/
- if (!file_pnum) {
- /* !file_pnum indicates an offset at or beyond the EOF; it is
- * perfectly valid for the format block driver to point to such
- * offsets, so catch it and mark everything as zero */
+ if (ret2 & BDRV_BLOCK_EOF &&
+ (!file_pnum || ret2 & BDRV_BLOCK_ZERO)) {
+ /*
+ * It is valid for the format block driver to read
+ * beyond the end of the underlying file's current
+ * size; such areas read as zero.
+ */
ret |= BDRV_BLOCK_ZERO;
} else {
/* Limit request to the range reported by the protocol driver */
@@ -1849,16 +1852,30 @@ static int64_t coroutine_fn bdrv_co_get_block_status_above(BlockDriverState *bs,
{
BlockDriverState *p;
int64_t ret = 0;
+ bool first = true;
assert(bs != base);
for (p = bs; p != base; p = backing_bs(p)) {
ret = bdrv_co_get_block_status(p, sector_num, nb_sectors, pnum, file);
- if (ret < 0 || ret & BDRV_BLOCK_ALLOCATED) {
+ if (ret < 0) {
+ break;
+ }
+ if (ret & BDRV_BLOCK_ZERO && ret & BDRV_BLOCK_EOF && !first) {
+ /*
+ * Reading beyond the end of the file continues to read
+ * zeroes, but we can only widen the result to the
+ * unallocated length we learned from an earlier
+ * iteration.
+ */
+ *pnum = nb_sectors;
+ }
+ if (ret & (BDRV_BLOCK_ZERO | BDRV_BLOCK_DATA)) {
break;
}
/* [sector_num, pnum] unallocated on this layer, which could be only
* the first part of [sector_num, nb_sectors]. */
nb_sectors = MIN(nb_sectors, *pnum);
+ first = false;
}
return ret;
}
diff --git a/tests/qemu-iotests/154 b/tests/qemu-iotests/154
index 687b8f3..d4dae83 100755
--- a/tests/qemu-iotests/154
+++ b/tests/qemu-iotests/154
@@ -334,8 +334,6 @@ $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
$QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
# Repeat with backing file holding unallocated cluster.
-# TODO: Note that this forces an allocation, because we aren't yet able to
-# quickly detect that reads beyond EOF of the backing file are always zero
CLUSTER_SIZE=2048 TEST_IMG="$TEST_IMG.base" _make_test_img $((size + 1024))
# Write at the front: sector-wise, the request is:
@@ -371,8 +369,6 @@ $QEMU_IO -c "alloc $size 2048" "$TEST_IMG" | _filter_qemu_io
$QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
# Repeat with backing file holding zero'd cluster
-# TODO: Note that this forces an allocation, because we aren't yet able to
-# quickly detect that reads beyond EOF of the backing file are always zero
$QEMU_IO -c "write -z $size 512" "$TEST_IMG.base" | _filter_qemu_io
# Write at the front: sector-wise, the request is:
diff --git a/tests/qemu-iotests/154.out b/tests/qemu-iotests/154.out
index b86f074..9e7abf2 100644
--- a/tests/qemu-iotests/154.out
+++ b/tests/qemu-iotests/154.out
@@ -310,19 +310,19 @@ wrote 512/512 bytes at offset 134217728
512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
2048/2048 bytes allocated at offset 128 MiB
[{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
-{ "start": 134217728, "length": 2048, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
+{ "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
wrote 512/512 bytes at offset 134219264
512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
2048/2048 bytes allocated at offset 128 MiB
[{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
-{ "start": 134217728, "length": 2048, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
+{ "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
wrote 1024/1024 bytes at offset 134218240
1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
2048/2048 bytes allocated at offset 128 MiB
[{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
-{ "start": 134217728, "length": 2048, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
+{ "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
wrote 2048/2048 bytes at offset 134217728
2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
@@ -336,19 +336,19 @@ wrote 512/512 bytes at offset 134217728
512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
2048/2048 bytes allocated at offset 128 MiB
[{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
-{ "start": 134217728, "length": 2048, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
+{ "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
wrote 512/512 bytes at offset 134219264
512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
2048/2048 bytes allocated at offset 128 MiB
[{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
-{ "start": 134217728, "length": 2048, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
+{ "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
wrote 1024/1024 bytes at offset 134218240
1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
2048/2048 bytes allocated at offset 128 MiB
[{ "start": 0, "length": 134217728, "depth": 1, "zero": true, "data": false},
-{ "start": 134217728, "length": 2048, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
+{ "start": 134217728, "length": 2048, "depth": 0, "zero": true, "data": false}]
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134219776 backing_file=TEST_DIR/t.IMGFMT.base
wrote 2048/2048 bytes at offset 134217728
2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
--
2.9.3
^ permalink raw reply related [flat|nested] 6+ messages in thread