Re: [libvirt] [PATCH 09/30] storagefile: Push extension_end calc to qcow2GetBackingStoreFormat

This is a step towards making this qcow2GetBackingStoreFormat into a generic qcow2 extensions parser Signed-off-by: Cole Robinson <crobinso(a)redhat.com&gt; ---

src/util/virstoragefile.c | 66 +++++++++++++++++++++------------------ 1 file changed, 35 insertions(+), 31 deletions(-) diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c index 4a3c9df7a2..b8f7faf580 100644 --- a/src/util/virstoragefile.c +++ b/src/util/virstoragefile.c @@ -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;