[libvirt] [PATCH 2/2] Storage : Fix cloning of raw, sparse volumes

[Ján Tomko]

On Mon, Jun 22, 2015 at 05:09:18PM +0530, Prerna Saxena wrote:
> From: Prerna Saxena <prerna at linux.vnet.ibm.com>
> Date: Mon, 22 Jun 2015 02:54:32 -0500
> 
> When virsh vol-clone is attempted on a raw file where capacity > allocation,
> the resulting cloned volume has a size that matches the virtual-size of
> the parent; in place of matching its actual, disk size.
> This patch fixes the cloned disk to have same _allocated_size_ as
> the parent file from which it was cloned.
> 
> Ref: http://www.redhat.com/archives/libvir-list/2015-May/msg00050.html
> 
> Also fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1130739
> 
> Signed-off-by: Prerna Saxena <prerna at linux.vnet.ibm.com>
> ---
>  src/storage/storage_backend.c | 10 +++++-----
>  src/storage/storage_driver.c  |  5 -----
>  2 files changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c
> index ce59f63..c99b718 100644
> --- a/src/storage/storage_backend.c
> +++ b/src/storage/storage_backend.c
> @@ -342,7 +342,7 @@ virStorageBackendCreateBlockFrom(virConnectPtr conn ATTRIBUTE_UNUSED,
>          goto cleanup;
>      }
>  
> -    remain = vol->target.allocation;
> +    remain = vol->target.capacity;
>  
>      if (inputvol) {
>          int res = virStorageBackendCopyToFD(vol, inputvol,
> @@ -397,7 +397,7 @@ createRawFile(int fd, virStorageVolDefPtr vol,
>                virStorageVolDefPtr inputvol,
>                bool reflink_copy)
>  {
> -    bool need_alloc = true;
> +    bool need_alloc = !(inputvol && (inputvol->target.capacity > inputvol->target.allocation));

Comparing 'inputvol->target.capacity > vol->target.allocation' would
allow creating a sparse volume from a non-sparse one and vice-versa
by specifying the correct allocation.

>      int ret = 0;
>      unsigned long long remain;
>  
> @@ -420,7 +420,7 @@ createRawFile(int fd, virStorageVolDefPtr vol,
>       * to writing zeroes block by block in case fallocate isn't
>       * available, and since we're going to copy data from another
>       * file it doesn't make sense to write the file twice. */
> -    if (vol->target.allocation) {
> +    if (vol->target.allocation && need_alloc) {
>          if (fallocate(fd, 0, 0, vol->target.allocation) == 0) {
>              need_alloc = false;
>          } else if (errno != ENOSYS && errno != EOPNOTSUPP) {
> @@ -433,14 +433,14 @@ createRawFile(int fd, virStorageVolDefPtr vol,
>      }
>  #endif
>  
> -    remain = vol->target.allocation;
> +    remain = vol->target.capacity;
>  
>      if (inputvol) {
>          /* allow zero blocks to be skipped if we've requested sparse
>           * allocation (allocation < capacity) or we have already
>           * been able to allocate the required space. */
>          bool want_sparse = !need_alloc ||
> -            (vol->target.allocation < inputvol->target.capacity);
> +            (inputvol->target.allocation < inputvol->target.capacity);

If allocation < capacity, then need_alloc is already false.

Jan
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