[libvirt] [PATCH 2/2] storage: try to perform btrfs COW copy if possible

[Ján Tomko]

On 01/13/2015 09:18 AM, Chen Hanxiao wrote:
> We don't take advantage of clone of btrfs.
> 
> So
> a)try to do a btrfs lightweight copy
> 
> b)fall back to a standard copy
>   if COW copy not supported.
> 
> Signed-off-by: Chen Hanxiao <chenhanxiao at cn.fujitsu.com>
> ---
>  include/libvirt/libvirt-storage.h |  1 +
>  src/storage/storage_backend.c     | 39 ++++++++++++++++++++++++++++++++-------
>  src/storage/storage_backend_fs.c  |  8 ++++++--
>  src/storage/storage_driver.c      |  4 +++-
>  4 files changed, 42 insertions(+), 10 deletions(-)
> 
> diff --git a/include/libvirt/libvirt-storage.h b/include/libvirt/libvirt-storage.h
> index 1f3087b..4ae42e1 100644
> --- a/include/libvirt/libvirt-storage.h
> +++ b/include/libvirt/libvirt-storage.h
> @@ -306,6 +306,7 @@ const char*             virStorageVolGetKey             (virStorageVolPtr vol);
>  
>  typedef enum {
>      VIR_STORAGE_VOL_CREATE_PREALLOC_METADATA = 1 << 0,
> +    VIR_STORAGE_VOL_CREATE_REFLINK = 1 << 1,

There should be some human-readable commentary after the flag, that will be
shown on our API reference page:
http://libvirt.org/html/libvirt-libvirt-storage.html#virStorageVolCreateFlags

>  } virStorageVolCreateFlags;
>  
>  virStorageVolPtr        virStorageVolCreateXML          (virStoragePoolPtr pool,
> diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c
> index 5ce3566..838398e 100644
> --- a/src/storage/storage_backend.c
> +++ b/src/storage/storage_backend.c
> @@ -187,7 +187,8 @@ virStorageBackendCopyToFD(virStorageVolDefPtr vol,
>                            virStorageVolDefPtr inputvol,
>                            int fd,
>                            unsigned long long *total,
> -                          bool want_sparse)
> +                          bool want_sparse,
> +                          bool reflink_copy)
>  {
>      int inputfd = -1;
>      int amtread = -1;
> @@ -226,6 +227,15 @@ virStorageBackendCopyToFD(virStorageVolDefPtr vol,
>          goto cleanup;
>      }
>  
> +    if (reflink_copy) {
> +        if (btrfsCloneFile(fd, inputfd) == -1) {
> +            VIR_DEBUG("btrfs clone not supported, try another way.");

If reflink copy is unsupported, I think we should just error out, as a full
copy won't be as fast / occupy as little space.

Also, this would fall back even on other errors.

The rest looks good to me.

Jan

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