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

[Kevin Wolf]

On Thu, Feb 14, 2013 at 09:40:22PM +0000, Blue Swirl wrote:
> 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) {

I consider the usefulness of this about the same as adding code in order to
silence gcc warnings. Just that a complaining gcc breaks the build whereas a
complaining Blue Swirl doesn't. But I'll do it here.

Kevin