[3/6] qcow2: simplify logic in qcow2_co_write_zeroes
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Message ID 1463227273-27523-4-git-send-email-den@openvz.org
State New
Headers show

Commit Message

Denis V. Lunev May 14, 2016, 12:01 p.m. UTC
Unaligned request could occupy only one cluster. This is true since the
previous commit. Simplify the code taking this considiration into
account.

There are no other changes so far.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2.c | 23 +++++------------------
 1 file changed, 5 insertions(+), 18 deletions(-)

Comments

Eric Blake May 16, 2016, 4:28 p.m. UTC | #1
On 05/14/2016 06:01 AM, Denis V. Lunev wrote:
> Unaligned request could occupy only one cluster. This is true since the

s/request could/requests will/

> previous commit. Simplify the code taking this considiration into

s/considiration/consideration/

> account.
> 
> There are no other changes so far.
> 
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qcow2.c | 23 +++++------------------
>  1 file changed, 5 insertions(+), 18 deletions(-)
> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 62febfc..9a54bbd 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2436,33 +2436,20 @@ static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
>      int tail = (sector_num + nb_sectors) % s->cluster_sectors;
>  
>      if (head != 0 || tail != 0) {
> -        int64_t cl_end = -1;
> +        int64_t cl_start = sector_num - head;
>  
> -        sector_num -= head;
> -        nb_sectors += head;
> +        assert(cl_start + s->cluster_sectors >= sector_num + nb_sectors);

In other words, the caller is now buggy if it ever passes us an
unaligned request that crosses cluster boundaries (the only requests
that can cross boundaries will be aligned).

With the grammar fix in the commit message,
Reviewed-by: Eric Blake <eblake@redhat.com>

Patch
diff mbox

diff --git a/block/qcow2.c b/block/qcow2.c
index 62febfc..9a54bbd 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2436,33 +2436,20 @@  static coroutine_fn int qcow2_co_write_zeroes(BlockDriverState *bs,
     int tail = (sector_num + nb_sectors) % s->cluster_sectors;
 
     if (head != 0 || tail != 0) {
-        int64_t cl_end = -1;
+        int64_t cl_start = sector_num - head;
 
-        sector_num -= head;
-        nb_sectors += head;
+        assert(cl_start + s->cluster_sectors >= sector_num + nb_sectors);
 
-        if (tail != 0) {
-            nb_sectors += s->cluster_sectors - tail;
-        }
+        sector_num = cl_start;
+        nb_sectors = s->cluster_sectors;
 
         if (!is_zero_cluster(bs, sector_num)) {
             return -ENOTSUP;
         }
 
-        if (nb_sectors > s->cluster_sectors) {
-            /* Technically the request can cover 2 clusters, f.e. 4k write
-               at s->cluster_sectors - 2k offset. One of these cluster can
-               be zeroed, one unallocated */
-            cl_end = sector_num + nb_sectors - s->cluster_sectors;
-            if (!is_zero_cluster(bs, cl_end)) {
-                return -ENOTSUP;
-            }
-        }
-
         qemu_co_mutex_lock(&s->lock);
         /* We can have new write after previous check */
-        if (!is_zero_cluster_top_locked(bs, sector_num) ||
-                (cl_end > 0 && !is_zero_cluster_top_locked(bs, cl_end))) {
+        if (!is_zero_cluster_top_locked(bs, sector_num)) {
             qemu_co_mutex_unlock(&s->lock);
             return -ENOTSUP;
         }