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storagefile: Push extension_end calc to qcow2GetBackingStoreFormat

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This is a step towards making this qcow2GetBackingStoreFormat into
a generic qcow2 extensions parser

Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Cole Robinson <crobinso@redhat.com>
This commit is contained in:
Cole Robinson 2019-10-04 19:57:55 -04:00
parent bd6b4646c7
commit 16fffd8257
1 changed files with 35 additions and 31 deletions
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66
src/util/virstoragefile.c
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@ -429,11 +429,11 @@ cowGetBackingStore(char **res,
static int
qcow2GetBackingStoreFormat(int *format,
const char *buf,
size_t buf_size,
size_t extension_end)
size_t buf_size)
{
size_t offset;
size_t extension_start;
size_t extension_end;
int version = virReadBufInt32BE(buf + QCOWX_HDR_VERSION);
if (version < 2) {
@ -447,6 +447,37 @@ qcow2GetBackingStoreFormat(int *format,
else
extension_start = virReadBufInt32BE(buf + QCOW2v3_HDR_SIZE);
/*
* Traditionally QCow2 files had a layout of
*
* [header]
* [backingStoreName]
*
* Although the backingStoreName typically followed
* the header immediately, this was not required by
* the format. By specifying a higher byte offset for
* the backing file offset in the header, it was
* possible to leave space between the header and
* start of backingStore.
*
* This hack is now used to store extensions to the
* qcow2 format:
*
* [header]
* [extensions]
* [backingStoreName]
*
* Thus the file region to search for extensions is
* between the end of the header (QCOW2_HDR_TOTAL_SIZE)
* and the start of the backingStoreName (offset)
*
* for qcow2 v3 images, the length of the header
* is stored at QCOW2v3_HDR_SIZE
*/
extension_end = virReadBufInt64BE(buf + QCOWX_HDR_BACKING_FILE_OFFSET);
if (extension_end > buf_size)
return -1;
/*
* The extensions take format of
*
@ -506,6 +537,7 @@ qcowXGetBackingStore(char **res,
if (buf_size < QCOWX_HDR_BACKING_FILE_OFFSET+8+4)
return BACKING_STORE_INVALID;
offset = virReadBufInt64BE(buf + QCOWX_HDR_BACKING_FILE_OFFSET);
if (offset > buf_size)
return BACKING_STORE_INVALID;
@ -529,35 +561,7 @@ qcowXGetBackingStore(char **res,
memcpy(*res, buf + offset, size);
(*res)[size] = '\0';
/*
* Traditionally QCow2 files had a layout of
*
* [header]
* [backingStoreName]
*
* Although the backingStoreName typically followed
* the header immediately, this was not required by
* the format. By specifying a higher byte offset for
* the backing file offset in the header, it was
* possible to leave space between the header and
* start of backingStore.
*
* This hack is now used to store extensions to the
* qcow2 format:
*
* [header]
* [extensions]
* [backingStoreName]
*
* Thus the file region to search for extensions is
* between the end of the header (QCOW2_HDR_TOTAL_SIZE)
* and the start of the backingStoreName (offset)
*
* for qcow2 v3 images, the length of the header
* is stored at QCOW2v3_HDR_SIZE
*/
if (qcow2GetBackingStoreFormat(format, buf, buf_size, offset) < 0)
if (qcow2GetBackingStoreFormat(format, buf, buf_size) < 0)
return BACKING_STORE_INVALID;
return BACKING_STORE_OK;