Re: [PATCH] kvm tools: Add read-only support for QCOW2 images

[Pekka Enberg <penberg@kernel.org>]

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On Tue, 19 Apr 2011, Prasad Joshi wrote:

> On Tue, Apr 19, 2011 at 10:07 PM, Pekka Enberg <penberg@kernel.org> wrote:
>       This patch extends the QCOW1 format to also support QCOW2 images as specified
>       by the following document:
>
>        http://people.gnome.org/~markmc/qcow-image-format.html
>
>       Cc: Asias He <asias.hejun@gmail.com>
>       Cc: Cyrill Gorcunov <gorcunov@gmail.com>
>       Cc: Prasad Joshi <prasadjoshi124@gmail.com>
>       Cc: Sasha Levin <levinsasha928@gmail.com>
>       Cc: Ingo Molnar <mingo@elte.hu>
>       Signed-off-by: Pekka Enberg <penberg@kernel.org>
>       ---
>        tools/kvm/include/kvm/qcow.h |   42 ++++++++++-
>        tools/kvm/qcow.c             |  177 +++++++++++++++++++++++++++++++++---------
>        2 files changed, 181 insertions(+), 38 deletions(-)
>
>       diff --git a/tools/kvm/include/kvm/qcow.h b/tools/kvm/include/kvm/qcow.h
>       index 4be2597..afd776d 100644
>       --- a/tools/kvm/include/kvm/qcow.h
>       +++ b/tools/kvm/include/kvm/qcow.h
>       @@ -4,9 +4,17 @@
>        #include <linux/types.h>
>
>        #define QCOW_MAGIC             (('Q' << 24) | ('F' << 16) | ('I' << 8) | 0xfb)
>       +
>        #define QCOW1_VERSION          1
>       +#define QCOW2_VERSION          2
>       +
>       +#define QCOW1_OFLAG_COMPRESSED (1LL << 63)
>       +
>       +#define QCOW1_OFLAG_MASK       QCOW1_OFLAG_COMPRESSED
>
>       -#define QCOW_OFLAG_COMPRESSED  (1LL << 63)
>       +#define QCOW2_OFLAG_COPIED     (1LL << 63)
>       +#define QCOW2_OFLAG_COMPRESSED (1LL << 62)
>       +#define QCOW2_OFLAG_MASK       (QCOW2_OFLAG_COPIED|QCOW2_OFLAG_COMPRESSED)
>
>        struct qcow_table {
>              u32                     table_size;
>       @@ -19,7 +27,16 @@ struct qcow {
>              int                     fd;
>        };
>
>       -struct qcow1_header {
>       +struct qcow_header {
>       +       u64                     size; /* in bytes */
>       +       u64                     l1_table_offset;
>       +       u32                     l1_size;
>       +       u8                      cluster_bits;
>       +       u8                      l2_bits;
>       +       uint64_t                oflag_mask;
>       +};
>       +
>       +struct qcow1_header_disk {
>              u32                     magic;
>              u32                     version;
>
>       @@ -36,6 +53,27 @@ struct qcow1_header {
>              u64                     l1_table_offset;
>        };
>
>       +struct qcow2_header_disk {
>       +       u32                     magic;
>       +       u32                     version;
>       +
>       +       u64                     backing_file_offset;
>       +       u32                     backing_file_size;
>       +
>       +       u32                     cluster_bits;
>       +       u64                     size; /* in bytes */
>       +       u32                     crypt_method;
>       +
>       +       u32                     l1_size;
>       +       u64                     l1_table_offset;
>       +
>       +       u64                     refcount_table_offset;
>       +       u32                     refcount_table_clusters;
>       +
>       +       u32                     nb_snapshots;
>       +       u64                     snapshots_offset;
>       +};
> 
> IMHO, as we start adding other features of QCOW, the two structures qcow2_header_disk and qcow_header might eventually become the same. 

No, the point of 'struct qcow2_header_disk' is to map to the on-disk 
representation. 'struct qcow_header' is the in-memory version of the data.

>       +       disk_image = disk_image__new(fd, h->size, &qcow1_disk_ops);
> 
> 
> qcow1_disk_ops can be changed to qcow_disk_ops.

Sure, there's more qcow1 prefixes that need fixing now as well.