Re: [Qemu-devel] [RFC PATCH v2 13/23] qcow2: handle_copied(): Implement non-zero host_offset

[Blue Swirl]

On Thu, Feb 14, 2013 at 9:40 AM, Kevin Wolf <address@hidden> wrote:
> Am 13.02.2013 22:17, schrieb Blue Swirl:
>> On Wed, Feb 13, 2013 at 1:22 PM, Kevin Wolf <address@hidden> wrote:
>>> Look only for clusters that start at a given physical offset.
>>>
>>> Signed-off-by: Kevin Wolf <address@hidden>
>>> ---
>>>  block/qcow2-cluster.c |   26 ++++++++++++++++++--------
>>>  1 files changed, 18 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
>>> index 5ce2c88..90fe36c 100644
>>> --- a/block/qcow2-cluster.c
>>> +++ b/block/qcow2-cluster.c
>>> @@ -827,8 +827,6 @@ static int handle_dependencies(BlockDriverState *bs, 
>>> uint64_t guest_offset,
>>>   *          the length of the area that can be written to.
>>>   *
>>>   *  -errno: in error cases
>>> - *
>>> - * TODO Make non-zero host_offset behave like describe above
>>>   */
>>>  static int handle_copied(BlockDriverState *bs, uint64_t guest_offset,
>>>      uint64_t *host_offset, uint64_t *bytes, QCowL2Meta **m)
>>> @@ -843,7 +841,6 @@ static int handle_copied(BlockDriverState *bs, uint64_t 
>>> guest_offset,
>>>
>>>      trace_qcow2_handle_copied(qemu_coroutine_self(), guest_offset, 
>>> *host_offset,
>>>                                *bytes);
>>> -    assert(*host_offset == 0);
>>>
>>>      /*
>>>       * Calculate the number of clusters to look for. We stop at L2 table
>>> @@ -867,6 +864,15 @@ static int handle_copied(BlockDriverState *bs, 
>>> uint64_t guest_offset,
>>>      if (qcow2_get_cluster_type(cluster_offset) == QCOW2_CLUSTER_NORMAL
>>>          && (cluster_offset & QCOW_OFLAG_COPIED))
>>>      {
>>> +        /* If a specific host_offset is required, check it */
>>> +        if (*host_offset != 0
>>> +            && (cluster_offset & L2E_OFFSET_MASK) != *host_offset)
>>> +        {
>>
>> Braces should cuddle with the previous line.
>
> Can we get rid of this rule for multiline ifs? Having the
> second/third/... line of the condition and the first line of the then
> branch with no clear separation severely hurts readability in my opinion.

Perhaps the problem is that the condition is long, it could be
rewritten in this style:
bool has_host_offset = *host_offset != 0;
bool offset_matches = (cluster_offset & L2E_OFFSET_MASK) != *host_offset;
if (has_host_offset && offset_matches) {

>
>>
>>> +            *bytes = 0;
>>> +            ret = 0;
>>> +            goto out;
>>> +        }
>>> +
>>>          /* We keep all QCOW_OFLAG_COPIED clusters */
>>>          keep_clusters =
>>>              count_contiguous_clusters(nb_clusters, s->cluster_size,
>
> Kevin