[Qemu-devel] [PATCH 08/12] qemu-img: conditionally zero out target on convert

[Peter Lieven <pl@kamp.de>]

if the target has_zero_init = 0, but supports efficiently
writing zeroes by unmapping we call bdrv_zeroize to
avoid fully allocating the target. this currently
is designed especially for iscsi.

Signed-off-by: Peter Lieven <pl@kamp.de>
---
 qemu-img.c |   22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index 3e5e388..6eaddc6 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1354,7 +1354,8 @@ static int img_convert(int argc, char **argv)
         }
     }
 
-    flags = BDRV_O_RDWR;
+    flags = BDRV_O_RDWR | BDRV_O_UNMAP;
+
     ret = bdrv_parse_cache_flags(cache, &flags);
     if (ret < 0) {
         error_report("Invalid cache option: %s", cache);
@@ -1386,12 +1387,13 @@ static int img_convert(int argc, char **argv)
         }
     }
 
+    ret = bdrv_get_info(out_bs, &bdi);
+    if (ret < 0) {
+        error_report("could not get block driver info");
+        goto out;
+    }
+
     if (compress) {
-        ret = bdrv_get_info(out_bs, &bdi);
-        if (ret < 0) {
-            error_report("could not get block driver info");
-            goto out;
-        }
         cluster_size = bdi.cluster_size;
         if (cluster_size <= 0 || cluster_size > IO_BUF_SIZE) {
             error_report("invalid cluster size");
@@ -1470,6 +1472,14 @@ static int img_convert(int argc, char **argv)
     } else {
         int has_zero_init = bdrv_has_zero_init(out_bs);
 
+        if (!has_zero_init && !out_baseimg && bdi.discard_write_zeroes) {
+            ret = bdrv_zeroize(out_bs, BDRV_REQ_MAY_UNMAP);
+            if (ret < 0) {
+                goto out;
+            }
+            has_zero_init = 1;
+        }
+
         sector_num = 0; // total number of sectors converted so far
         nb_sectors = total_sectors - sector_num;
         if (nb_sectors != 0) {
-- 
1.7.9.5