[PATCH v4 2/2] 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.

Overall, it seems that only VPC and old QEMUs need to be ignored as all new
creator apps seem to have reliable current_size. Invert the logic and make
'current_size' method the default to avoid adding every new creator app to
the list.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 block/vpc.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/block/vpc.c b/block/vpc.c
index fb0ded1c4344..a5f626baf04a 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -237,6 +237,7 @@ static void vpc_parse_options(BlockDriverState *bs, 
QemuOpts *opts,
  *      'd2v '  :  current_size     Disk2vhd
  *      'tap\0' :  current_size     XenServer
  *      'CTXS'  :  current_size     XenConverter
+ *      'wa\0\0':  current_size     Azure
  *
  *  The user can override the table values via drive options, however
  *  even with an override we will still use current_size for images
@@ -244,11 +245,8 @@ static void vpc_parse_options(BlockDriverState *bs, 
QemuOpts *opts,
  */
 static bool vpc_ignore_current_size(VHDFooter *footer)
 {
-    return !!strncmp(footer->creator_app, "win ", 4) &&
-           !!strncmp(footer->creator_app, "qem2", 4) &&
-           !!strncmp(footer->creator_app, "d2v ", 4) &&
-           !!strncmp(footer->creator_app, "CTXS", 4) &&
-           !!memcmp(footer->creator_app, "tap", 4));
+    return !strncmp(footer->creator_app, "vpc ", 4) ||
+           !strncmp(footer->creator_app, "qemu", 4);
 }
 
 static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
-- 
2.47.0