[Qemu-devel] [PATCH v2 1/4] qemu-img: Fix preallocation with -S 0 for convert

[Max Reitz <mreitz@redhat.com>]

When passing -S 0 to qemu-img convert, the target image is supposed to
be fully allocated. Right now, this is not the case if the source image
contains areas which bdrv_get_block_status() reports as being zero.

This patch changes a zeroed area's status from BLK_ZERO to BLK_DATA
before invoking convert_write() if -S 0 has been specified. In addition,
the check whether convert_read() actually needs to do anything
(basically only if the current area is a BLK_DATA area) is pulled out of
that function to the caller.

If -S 0 has been specified, zeroed areas need to be written as data to
the output, thus they then have to be accounted when calculating the
progress made.

This patch changes the reference output for iotest 122; contrary to what
it assumed, -S 0 really should allocate everything in the output, not
just areas that are filled with zeros (as opposed to being zeroed).

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 qemu-img.c                 | 26 +++++++++++++++-----------
 tests/qemu-iotests/122.out |  6 ++----
 2 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index 29eae2a..b2e07bb 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1507,10 +1507,6 @@ static int convert_read(ImgConvertState *s, int64_t sector_num, int nb_sectors,
     int n;
     int ret;
 
-    if (s->status == BLK_ZERO || s->status == BLK_BACKING_FILE) {
-        return 0;
-    }
-
     assert(nb_sectors <= s->buf_sectors);
     while (nb_sectors > 0) {
         BlockBackend *blk;
@@ -1648,7 +1644,8 @@ static int convert_do_copy(ImgConvertState *s)
             ret = n;
             goto fail;
         }
-        if (s->status == BLK_DATA) {
+        if (s->status == BLK_DATA || (!s->min_sparse && s->status == BLK_ZERO))
+        {
             s->allocated_sectors += n;
         }
         sector_num += n;
@@ -1668,17 +1665,24 @@ static int convert_do_copy(ImgConvertState *s)
             ret = n;
             goto fail;
         }
-        if (s->status == BLK_DATA) {
+        if (s->status == BLK_DATA || (!s->min_sparse && s->status == BLK_ZERO))
+        {
             allocated_done += n;
             qemu_progress_print(100.0 * allocated_done / s->allocated_sectors,
                                 0);
         }
 
-        ret = convert_read(s, sector_num, n, buf);
-        if (ret < 0) {
-            error_report("error while reading sector %" PRId64
-                         ": %s", sector_num, strerror(-ret));
-            goto fail;
+        if (s->status == BLK_DATA) {
+            ret = convert_read(s, sector_num, n, buf);
+            if (ret < 0) {
+                error_report("error while reading sector %" PRId64
+                             ": %s", sector_num, strerror(-ret));
+                goto fail;
+            }
+        } else if (!s->min_sparse && s->status == BLK_ZERO) {
+            n = MIN(n, s->buf_sectors);
+            memset(buf, 0, n * BDRV_SECTOR_SIZE);
+            s->status = BLK_DATA;
         }
 
         ret = convert_write(s, sector_num, n, buf);
diff --git a/tests/qemu-iotests/122.out b/tests/qemu-iotests/122.out
index 0068e96..98814de 100644
--- a/tests/qemu-iotests/122.out
+++ b/tests/qemu-iotests/122.out
@@ -112,16 +112,14 @@ read 3145728/3145728 bytes at offset 0
 3 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 read 63963136/63963136 bytes at offset 3145728
 61 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-[{ "start": 0, "length": 6291456, "depth": 0, "zero": false, "data": true, "offset": 327680},
-{ "start": 6291456, "length": 60817408, "depth": 0, "zero": true, "data": false}]
+[{ "start": 0, "length": 67108864, "depth": 0, "zero": false, "data": true, "offset": 327680}]
 
 convert -c -S 0:
 read 3145728/3145728 bytes at offset 0
 3 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 read 63963136/63963136 bytes at offset 3145728
 61 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-[{ "start": 0, "length": 6291456, "depth": 0, "zero": false, "data": true},
-{ "start": 6291456, "length": 60817408, "depth": 0, "zero": true, "data": false}]
+[{ "start": 0, "length": 67108864, "depth": 0, "zero": false, "data": true}]
 Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
 wrote 33554432/33554432 bytes at offset 0
 32 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-- 
2.7.4