Am 22.01.2014 um 07:57 hat Hu Tao geschrieben:
> n_start can be actually calculated from offset. The number of
> sectors to be allocated(n_end - n_start) can be passed in in
> num. By removing n_start and n_end, we can save two parameters.
>
> The side effect is there is a bug in qcow2.c:preallocate() that
> passes incorrect n_start to qcow2_alloc_cluster_offset() is
> fixed. The bug can be triggerred by a larger cluster size than
> the default value(65536), for example:
>
> ./qemu-img create -f qcow2 \
> -o 'cluster_size=131072,preallocation=metadata' file.img 4G
>
> Reviewed-by: Max Reitz <mre...@redhat.com>
> Signed-off-by: Hu Tao <hu...@cn.fujitsu.com>
> ---
> block/qcow2-cluster.c | 14 ++++++--------
> block/qcow2.c | 6 +++---
> block/qcow2.h | 2 +-
> trace-events | 2 +-
> 4 files changed, 11 insertions(+), 13 deletions(-)
>
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 8534084..c57f39d 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1182,7 +1182,7 @@ fail:
> * Return 0 on success and -errno in error cases
> */
> int qcow2_alloc_cluster_offset(BlockDriverState *bs, uint64_t offset,
> - int n_start, int n_end, int *num, uint64_t *host_offset, QCowL2Meta **m)
> + int *num, uint64_t *host_offset, QCowL2Meta **m)
> {
> BDRVQcowState *s = bs->opaque;
> uint64_t start, remaining;
> @@ -1190,15 +1190,13 @@ int qcow2_alloc_cluster_offset(BlockDriverState *bs,
> uint64_t offset,
> uint64_t cur_bytes;
> int ret;
>
> - trace_qcow2_alloc_clusters_offset(qemu_coroutine_self(), offset,
> - n_start, n_end);
> + trace_qcow2_alloc_clusters_offset(qemu_coroutine_self(), offset, *num);
>
> - assert(n_start * BDRV_SECTOR_SIZE == offset_into_cluster(s, offset));
> - offset = start_of_cluster(s, offset);
> + assert((offset & ~BDRV_SECTOR_MASK) == 0);
>
> again:
> - start = offset + (n_start << BDRV_SECTOR_BITS);
> - remaining = (n_end - n_start) << BDRV_SECTOR_BITS;
> + start = offset;
> + remaining = *num << BDRV_SECTOR_BITS;
> cluster_offset = 0;
> *host_offset = 0;
> cur_bytes = 0;
> @@ -1284,7 +1282,7 @@ again:
> }
> }
>
> - *num = (n_end - n_start) - (remaining >> BDRV_SECTOR_BITS);
> + *num -= remaining >> BDRV_SECTOR_BITS;
> assert(*num > 0);
> assert(*host_offset != 0);
>
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 8ec9db1..a0596ec 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1016,14 +1016,14 @@ static coroutine_fn int
> qcow2_co_writev(BlockDriverState *bs,
>
> trace_qcow2_writev_start_part(qemu_coroutine_self());
> index_in_cluster = sector_num & (s->cluster_sectors - 1);
> - n_end = index_in_cluster + remaining_sectors;
> + cur_nr_sectors = remaining_sectors;
> if (s->crypt_method &&
> n_end > QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors) {
> n_end = QCOW_MAX_CRYPT_CLUSTERS * s->cluster_sectors;
> }
You don't want to change n_end here any more, this should affect
cur_nr_sectors now. n_end becomes completely unused then and can be
removed.
I wonder why the compiler doesn't complain here, this is uninitialised
use and a write-only variable at the same time.
Kevin
