[Qemu-devel] [PULL 27/42] qemu-img: always probe the input image for allocated sectors

[Stefan Hajnoczi <stefanha@redhat.com>]

From: Paolo Bonzini <pbonzini@redhat.com>

qemu-img convert can assume "that sectors which are unallocated in the
input image are present in both the output's and input's base images".

However it is only doing this if the output image returns true for
bdrv_has_zero_init().  Testing bdrv_has_zero_init() does not make much
sense if the output image is copy-on-write, because a copy-on-write
image is never initialized to zero (it is initialized to the content
of the backing file).

There is nothing here that makes has_zero_init images special.  The
input and output must be equal for the operation to make sense, and
that's it.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 qemu-img.c | 40 +++++++++++++++++++---------------------
 1 file changed, 19 insertions(+), 21 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index 27cc006..5cc579d 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1502,28 +1502,26 @@ static int img_convert(int argc, char **argv)
                 n = bs_offset + bs_sectors - sector_num;
             }
 
-            if (has_zero_init) {
-                /* If the output image is being created as a copy on write image,
-                   assume that sectors which are unallocated in the input image
-                   are present in both the output's and input's base images (no
-                   need to copy them). */
-                if (out_baseimg) {
-                    ret = bdrv_is_allocated(bs[bs_i], sector_num - bs_offset,
-                                            n, &n1);
-                    if (ret < 0) {
-                        error_report("error while reading metadata for sector "
-                                     "%" PRId64 ": %s",
-                                     sector_num - bs_offset, strerror(-ret));
-                        goto out;
-                    }
-                    if (!ret) {
-                        sector_num += n1;
-                        continue;
-                    }
-                    /* The next 'n1' sectors are allocated in the input image. Copy
-                       only those as they may be followed by unallocated sectors. */
-                    n = n1;
+            /* If the output image is being created as a copy on write image,
+               assume that sectors which are unallocated in the input image
+               are present in both the output's and input's base images (no
+               need to copy them). */
+            if (out_baseimg) {
+                ret = bdrv_is_allocated(bs[bs_i], sector_num - bs_offset,
+                                        n, &n1);
+                if (ret < 0) {
+                    error_report("error while reading metadata for sector "
+                                 "%" PRId64 ": %s",
+                                 sector_num - bs_offset, strerror(-ret));
+                    goto out;
+                }
+                if (!ret) {
+                    sector_num += n1;
+                    continue;
                 }
+                /* The next 'n1' sectors are allocated in the input image. Copy
+                   only those as they may be followed by unallocated sectors. */
+                n = n1;
             } else {
                 n1 = n;
             }
-- 
1.8.3.1