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qcow2 spec: Describe string header extensions

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Be more specific about the string representation in header extensions.

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Kevin Wolf 2019-03-07 17:49:55 +01:00
parent 9c2b28e458
commit e88153ea9a
1 changed files with 12 additions and 2 deletions
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14
docs/interop/qcow2.txt
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@ -170,11 +170,11 @@ be stored. Each extension has a structure like the following:
Byte 0 - 3: Header extension type:
0x00000000 - End of the header extension area
0xE2792ACA - Backing file format name
0xE2792ACA - Backing file format name string
0x6803f857 - Feature name table
0x23852875 - Bitmaps extension
0x0537be77 - Full disk encryption header pointer
0x44415441 - External data file name
0x44415441 - External data file name string
other - Unknown header extension, can be safely
ignored
@ -196,6 +196,16 @@ data of compatible features that it doesn't support. Compatible features that
need space for additional data can use a header extension.
== String header extensions ==
Some header extensions (such as the backing file format name and the external
data file name) are just a single string. In this case, the header extension
length is the string length and the string is not '\0' terminated. (The header
extension padding can make it look like a string is '\0' terminated, but
neither is padding always necessary nor is there a guarantee that zero bytes
are used for padding.)
== Feature name table ==
The feature name table is an optional header extension that contains the name