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authorKevin Wolf <kwolf@redhat.com>2019-03-07 17:49:55 +0100
committerKevin Wolf <kwolf@redhat.com>2019-03-08 12:26:46 +0100
commite88153ea9a40009a8ae7648282c0eac1b7f5494f (patch)
tree656eb41a5551b9d6a4d9b345bf796fe166a15a8a /docs/interop/qcow2.txt
parent9c2b28e4584f51896e4889239464ec0e469b96fa (diff)
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qcow2 spec: Describe string header extensions
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>
Diffstat (limited to 'docs/interop/qcow2.txt')
-rw-r--r--docs/interop/qcow2.txt14
1 files changed, 12 insertions, 2 deletions
diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index bfb97cf..8c3098d 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -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