Re: [Qemu-devel] [PATCH] qcow2: fix preallocation with metadata on bare block device

[Ivan Ren]

ping for review

On Tue, May 8, 2018 at 8:27 PM Ivan Ren <address@hidden> wrote:

> Create a qcow2 directly on bare block device with
> "-o preallocation=metadata" option. When read this qcow2, it will
> return dirty data of block device. This patch add QCOW_OFLAG_ZERO
> for all preallocated l2 entry if the underlying device is a bare
> block device.
>
> Signed-off-by: Ivan Ren <address@hidden>
> ---
>  block/qcow2-cluster.c |  5 +++--
>  block/qcow2.c         | 19 ++++++++++++++++---
>  block/qcow2.h         |  3 ++-
>  3 files changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 1aee726..b9e0ceb 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -919,7 +919,8 @@ fail:
>      return ret;
>  }
>
> -int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m)
> +int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m,
> +                                uint64_t flags)
>  {
>      BDRVQcow2State *s = bs->opaque;
>      int i, j = 0, l2_index, ret;
> @@ -969,7 +970,7 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs,
> QCowL2Meta *m)
>          }
>
>          l2_slice[l2_index + i] = cpu_to_be64((cluster_offset +
> -                    (i << s->cluster_bits)) | QCOW_OFLAG_COPIED);
> +                    (i << s->cluster_bits)) | QCOW_OFLAG_COPIED | flags);
>       }
>
>
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 2f36e63..093735c 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2044,7 +2044,7 @@ static coroutine_fn int
> qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
>          while (l2meta != NULL) {
>              QCowL2Meta *next;
>
> -            ret = qcow2_alloc_cluster_link_l2(bs, l2meta);
> +            ret = qcow2_alloc_cluster_link_l2(bs, l2meta, 0);
>              if (ret < 0) {
>                  goto fail;
>              }
> @@ -2534,6 +2534,7 @@ static void coroutine_fn preallocate_co(void *opaque)
>      uint64_t host_offset = 0;
>      unsigned int cur_bytes;
>      int ret;
> +    struct stat st;
>      QCowL2Meta *meta;
>
>      qemu_co_mutex_lock(&s->lock);
> @@ -2552,7 +2553,19 @@ static void coroutine_fn preallocate_co(void
> *opaque)
>          while (meta) {
>              QCowL2Meta *next = meta->next;
>
> -            ret = qcow2_alloc_cluster_link_l2(bs, meta);
> +            /* Check the underlying device type.
> +             * If the underlying device is a block device, we add
> +             * QCOW_OFLAG_ZERO for all preallocated l2 entry to ignore
> dirty
> +             * data on block device.
> +             * If the underlying device can't be used with stat(return <
> 0),
> +             * treat it as a regular file.
> +             */
> +            if (stat(bs->filename, &st) < 0 || !S_ISBLK(st.st_mode)) {
> +                ret = qcow2_alloc_cluster_link_l2(bs, meta, 0);
> +            } else {
> +                ret = qcow2_alloc_cluster_link_l2(bs, meta,
> QCOW_OFLAG_ZERO);
> +            }
> +
>              if (ret < 0) {
>                  qcow2_free_any_clusters(bs, meta->alloc_offset,
>                                          meta->nb_clusters,
> QCOW2_DISCARD_NEVER);
> @@ -3458,7 +3471,7 @@ static int qcow2_truncate(BlockDriverState *bs,
> int64_t offset,
>              };
>              qemu_co_queue_init(&allocation.dependent_requests);
>
> -            ret = qcow2_alloc_cluster_link_l2(bs, &allocation);
> +            ret = qcow2_alloc_cluster_link_l2(bs, &allocation, 0);
>              if (ret < 0) {
>                  error_setg_errno(errp, -ret, "Failed to update L2
> tables");
>                  qcow2_free_clusters(bs, host_offset,
> diff --git a/block/qcow2.h b/block/qcow2.h
> index adf5c39..9a59602 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -617,7 +617,8 @@ uint64_t
> qcow2_alloc_compressed_cluster_offset(BlockDriverState *bs,
>                                           uint64_t offset,
>                                           int compressed_size);
>
> -int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m);
> +int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m,
> +                                uint64_t flags);
>  int qcow2_cluster_discard(BlockDriverState *bs, uint64_t offset,
>                            uint64_t bytes, enum qcow2_discard_type type,
>                            bool full_discard);
> --
> 1.8.3.1
>
>