[Qemu-devel] [PATCH 3/8] block: Do not truncate file node when formatting

[Max Reitz <mreitz@redhat.com>]

There is no reason why the format drivers need to truncate the protocol
node when formatting it.  When using the old .bdrv_co_create_ops()
interface, the file will be created with no size option anyway, which
generally gives it a size of 0.  (Exceptions are block devices, which
cannot be truncated anyway.)

When using blockdev-create, the user must have given the file node some
size anyway, so there is no reason why we should override that.

qed is an exception, it needs the file to start completely empty (as
explained by c743849bee7333c7ef256b7e12e34ed6f907064f).

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/parallels.c | 5 -----
 block/qcow.c      | 5 -----
 block/qcow2.c     | 6 ------
 3 files changed, 16 deletions(-)

diff --git a/block/parallels.c b/block/parallels.c
index 7cd2714b69..905cac35c6 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -563,11 +563,6 @@ static int coroutine_fn parallels_co_create(BlockdevCreateOptions* opts,
     blk_set_allow_write_beyond_eof(blk, true);
 
     /* Create image format */
-    ret = blk_truncate(blk, 0, PREALLOC_MODE_OFF, errp);
-    if (ret < 0) {
-        goto out;
-    }
-
     bat_entries = DIV_ROUND_UP(total_size, cl_size);
     bat_sectors = DIV_ROUND_UP(bat_entry_off(bat_entries), cl_size);
     bat_sectors = (bat_sectors *  cl_size) >> BDRV_SECTOR_BITS;
diff --git a/block/qcow.c b/block/qcow.c
index 5bdf72ba33..17705015ca 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -858,11 +858,6 @@ static int coroutine_fn qcow_co_create(BlockdevCreateOptions *opts,
     blk_set_allow_write_beyond_eof(qcow_blk, true);
 
     /* Create image format */
-    ret = blk_truncate(qcow_blk, 0, PREALLOC_MODE_OFF, errp);
-    if (ret < 0) {
-        goto exit;
-    }
-
     memset(&header, 0, sizeof(header));
     header.magic = cpu_to_be32(QCOW_MAGIC);
     header.version = cpu_to_be32(QCOW_VERSION);
diff --git a/block/qcow2.c b/block/qcow2.c
index 4d16393e61..4978ccc7be 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -3186,12 +3186,6 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
     }
     blk_set_allow_write_beyond_eof(blk, true);
 
-    /* Clear the protocol layer and preallocate it if necessary */
-    ret = blk_truncate(blk, 0, PREALLOC_MODE_OFF, errp);
-    if (ret < 0) {
-        goto out;
-    }
-
     /* Write the header */
     QEMU_BUILD_BUG_ON((1 << MIN_CLUSTER_BITS) < sizeof(*header));
     header = g_malloc0(cluster_size);
-- 
2.21.0