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

[Daniel Henrique Barboza]

On 10/7/19 6:49 PM, Cole Robinson wrote:
> This is a step towards making this qcow2GetBackingStoreFormat into
> a generic qcow2 extensions parser
>
> Signed-off-by: Cole Robinson <crobinso at redhat.com>
> ---

Reviewed-by: Daniel Henrique Barboza <danielhb413 at gmail.com>


>   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;