Instead of calling perform_cow() twice with a different COW region
each time, call it just once and make perform_cow() handle both
regions.

This patch simply moves code around. The next one will do the actual
reordering of the COW operations.

Signed-off-by: Alberto Garcia <berto@igalia.com>
---
 block/qcow2-cluster.c | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 6757875ec9..59a0ffba1a 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -414,6 +414,10 @@ static int coroutine_fn do_perform_cow(BlockDriverState *bs,
     struct iovec iov;
     int ret;
 
+    if (bytes == 0) {
+        return 0;
+    }
+
     iov.iov_len = bytes;
     iov.iov_base = qemu_try_blockalign(bs, iov.iov_len);
     if (iov.iov_base == NULL) {
@@ -751,31 +755,40 @@ uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
     return cluster_offset;
 }
 
-static int perform_cow(BlockDriverState *bs, QCowL2Meta *m, Qcow2COWRegion *r)
+static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
 {
     BDRVQcow2State *s = bs->opaque;
+    Qcow2COWRegion *start = &m->cow_start;
+    Qcow2COWRegion *end = &m->cow_end;
     int ret;
 
-    if (r->nb_bytes == 0) {
+    if (start->nb_bytes == 0 && end->nb_bytes == 0) {
         return 0;
     }
 
     qemu_co_mutex_unlock(&s->lock);
-    ret = do_perform_cow(bs, m->offset, m->alloc_offset, r->offset, r->nb_bytes);
+    ret = do_perform_cow(bs, m->offset, m->alloc_offset,
+                         start->offset, start->nb_bytes);
+    if (ret < 0) {
+        goto fail;
+    }
+
+    ret = do_perform_cow(bs, m->offset, m->alloc_offset,
+                         end->offset, end->nb_bytes);
+
+fail:
     qemu_co_mutex_lock(&s->lock);
 
-    if (ret < 0) {
-        return ret;
-    }
-
     /*
      * Before we update the L2 table to actually point to the new cluster, we
      * need to be sure that the refcounts have been increased and COW was
      * handled.
      */
-    qcow2_cache_depends_on_flush(s->l2_table_cache);
+    if (ret == 0) {
+        qcow2_cache_depends_on_flush(s->l2_table_cache);
+    }
 
-    return 0;
+    return ret;
 }
 
 int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
@@ -795,12 +808,7 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
     }
 
     /* copy content of unmodified sectors */
-    ret = perform_cow(bs, m, &m->cow_start);
-    if (ret < 0) {
-        goto err;
-    }
-
-    ret = perform_cow(bs, m, &m->cow_end);
+    ret = perform_cow(bs, m);
     if (ret < 0) {
         goto err;
     }
-- 
2.11.0

Am 23.05.2017 um 13:22 hat Alberto Garcia geschrieben:
> Instead of calling perform_cow() twice with a different COW region
> each time, call it just once and make perform_cow() handle both
> regions.
> 
> This patch simply moves code around. The next one will do the actual
> reordering of the COW operations.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/qcow2-cluster.c | 38 +++++++++++++++++++++++---------------
>  1 file changed, 23 insertions(+), 15 deletions(-)
> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 6757875ec9..59a0ffba1a 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -414,6 +414,10 @@ static int coroutine_fn do_perform_cow(BlockDriverState *bs,
>      struct iovec iov;
>      int ret;
>  
> +    if (bytes == 0) {
> +        return 0;
> +    }
> +
>      iov.iov_len = bytes;
>      iov.iov_base = qemu_try_blockalign(bs, iov.iov_len);
>      if (iov.iov_base == NULL) {
> @@ -751,31 +755,40 @@ uint64_t qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
>      return cluster_offset;
>  }
>  
> -static int perform_cow(BlockDriverState *bs, QCowL2Meta *m, Qcow2COWRegion *r)
> +static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
>  {
>      BDRVQcow2State *s = bs->opaque;
> +    Qcow2COWRegion *start = &m->cow_start;
> +    Qcow2COWRegion *end = &m->cow_end;
>      int ret;
>  
> -    if (r->nb_bytes == 0) {
> +    if (start->nb_bytes == 0 && end->nb_bytes == 0) {
>          return 0;
>      }

With this change, it can now happen that we call do_perform_cow() with
bytes == 0. Maybe it would be better for do_perform_cow() to check bytes
first so that it doesn't bdrv_co_preadv/pwritev() for 0 bytes?

Kevin

On Fri 26 May 2017 10:11:29 AM CEST, Kevin Wolf <kwolf@redhat.com> wrote:
>> --- a/block/qcow2-cluster.c
>> +++ b/block/qcow2-cluster.c
>> @@ -414,6 +414,10 @@ static int coroutine_fn do_perform_cow(BlockDriverState *bs,
>>      struct iovec iov;
>>      int ret;
>>  
>> +    if (bytes == 0) {
>> +        return 0;
>> +    }
>> +

   [...]

>> +static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
>>  {
>>      BDRVQcow2State *s = bs->opaque;
>> +    Qcow2COWRegion *start = &m->cow_start;
>> +    Qcow2COWRegion *end = &m->cow_end;
>>      int ret;
>>  
>> -    if (r->nb_bytes == 0) {
>> +    if (start->nb_bytes == 0 && end->nb_bytes == 0) {
>>          return 0;
>>      }
>
> With this change, it can now happen that we call do_perform_cow() with
> bytes == 0.

Yes, but see the change I made to do_perform_cow() in the same patch
(quoted above).

Berto

Am 26.05.2017 um 11:10 hat Alberto Garcia geschrieben:
> On Fri 26 May 2017 10:11:29 AM CEST, Kevin Wolf <kwolf@redhat.com> wrote:
> >> --- a/block/qcow2-cluster.c
> >> +++ b/block/qcow2-cluster.c
> >> @@ -414,6 +414,10 @@ static int coroutine_fn do_perform_cow(BlockDriverState *bs,
> >>      struct iovec iov;
> >>      int ret;
> >>  
> >> +    if (bytes == 0) {
> >> +        return 0;
> >> +    }
> >> +
> 
>    [...]
> 
> >> +static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
> >>  {
> >>      BDRVQcow2State *s = bs->opaque;
> >> +    Qcow2COWRegion *start = &m->cow_start;
> >> +    Qcow2COWRegion *end = &m->cow_end;
> >>      int ret;
> >>  
> >> -    if (r->nb_bytes == 0) {
> >> +    if (start->nb_bytes == 0 && end->nb_bytes == 0) {
> >>          return 0;
> >>      }
> >
> > With this change, it can now happen that we call do_perform_cow() with
> > bytes == 0.
> 
> Yes, but see the change I made to do_perform_cow() in the same patch
> (quoted above).

Wait... How did you manage to hack my email account and insert this
retroactively? :-)

Sorry for the noise then, I must have been looking at the source code of
the wrong commit.

Kevin