diff --git a/block/io.c b/block/io.c
index 9bba730a7e..2de7c77983 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1711,15 +1711,16 @@ 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.
@@ -1740,7 +1741,7 @@ 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;
@@ -1751,6 +1752,9 @@ 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);
}
@@ -1799,10 +1803,13 @@ 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 */
@@ -1814,6 +1821,9 @@ 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;
}
@@ -1826,16 +1836,30 @@ 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/include/block/block.h b/include/block/block.h
index 85e4be7462..4c149adb17 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -129,6 +129,7 @@ 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
@@ -157,6 +158,7 @@ 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/tests/qemu-iotests/154 b/tests/qemu-iotests/154
index dd8a426dad..fde03b0dc8 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 d8485eeff2..fa3673317f 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)