[PATCH v2] vpc: Read images exported from Azure correctly

[Vitaly Kuznetsov]

It was found that 'qemu-nbd' is not able to work with some disk images
exported from Azure. Looking at the 512b footer (which contains VPC
metadata):

00000000  63 6f 6e 65 63 74 69 78  00 00 00 02 00 01 00 00  |conectix........|
00000010  ff ff ff ff ff ff ff ff  2e c7 9b 96 77 61 00 00  |............wa..|
00000020  00 07 00 00 57 69 32 6b  00 00 00 01 40 00 00 00  |....Wi2k....@...|
00000030  00 00 00 01 40 00 00 00  28 a2 10 3f 00 00 00 02  |....@...(..?....|
00000040  ff ff e7 47 8c 54 df 94  bd 35 71 4c 94 5f e5 44  |...G.T...5qL._.D|
00000050  44 53 92 1a 00 00 00 00  00 00 00 00 00 00 00 00  |DS..............|
00000060  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|

we can see that Azure uses a different 'Creator application' --
'wa\0\0' (offset 0x1c, likely reads as 'Windows Azure') and QEMU uses this
field to determine how it can get image size. Apparently, Azure uses 'new'
method, just like Hyper-V.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Alternatively, we can probably make 'current_size' the default and only use
CHS for 'vpc '/'qemu'.
---
 block/vpc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/vpc.c b/block/vpc.c
index d95a204612b7..b67798697c15 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -321,6 +321,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, 
int flags,
      *      'qemu'  :  CHS              QEMU (uses disk geometry)
      *      'qem2'  :  current_size     QEMU (uses current_size)
      *      'win '  :  current_size     Hyper-V
+     *      'wa\0\0':  current_size     Azure
      *      'd2v '  :  current_size     Disk2vhd
      *      'tap\0' :  current_size     XenServer
      *      'CTXS'  :  current_size     XenConverter
@@ -330,6 +331,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, 
int flags,
      *  that have CHS geometry of the maximum size.
      */
     use_chs = (!!strncmp(footer->creator_app, "win ", 4) &&
+               !!memcmp(footer->creator_app, "wa\0", 4) &&
                !!strncmp(footer->creator_app, "qem2", 4) &&
                !!strncmp(footer->creator_app, "d2v ", 4) &&
                !!strncmp(footer->creator_app, "CTXS", 4) &&
-- 
2.47.0