On Tue, Jan 06, 2015 at 06:48:04PM +0100, Peter Wu wrote:
> DMG files have a variable length with a UDIF trailer at the end of a
> file. This UDIF trailer is essential as it describes the contents of
> the image. At the moment however, the start of this trailer is almost
> always incorrect as bdrv_getlength() returns a multiple of the block
> size (rounded up). This results in a failure to recognize DMG files,
> resulting in Invalid argument (EINVAL) errors.
>
> As there is no API to retrieve the real file size, look for the magic
> header in the last two sectors to find the start of this 512-byte UDIF
> trailer (the "koly" block).
>
> The resource fork offset ("info_begin") has its offset adjusted as the
> initial value of offset does not mean "end of file" anymore, but "begin
> of UDIF trailer".
>
> Signed-off-by: Peter Wu <pe...@lekensteyn.nl>
> Reviewed-by: John Snow <js...@redhat.com>
> ---
> v2: added R-b, set errp as suggested by Stefan Hajnoczi
> ---
> block/dmg.c | 49 +++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 45 insertions(+), 4 deletions(-)
>
> diff --git a/block/dmg.c b/block/dmg.c
> index e455886..9183459 100644
> --- a/block/dmg.c
> +++ b/block/dmg.c
> @@ -131,6 +131,48 @@ static void update_max_chunk_size(BDRVDMGState *s,
> uint32_t chunk,
> }
> }
>
> +static int64_t dmg_find_koly_offset(BlockDriverState *file_bs, Error **errp)
> +{
> + int64_t length;
> + int64_t offset = 0;
> + uint8_t buffer[515];
> + int i, ret;
> +
> + /* bdrv_getlength returns a multiple of block size (512), rounded up.
> Since
> + * dmg images can have odd sizes, try to look for the "koly" magic which
> + * marks the begin of the UDIF trailer (512 bytes). This magic can be
> found
> + * in the last 511 bytes of the second-last sector or the first 4 bytes
> of
> + * the last sector (search space: 515 bytes) */
> + length = bdrv_getlength(file_bs);
> + if (length < 0) {
> + error_setg_errno(errp, -length,
> + "Failed to get file size while reading UDIF trailer");
> + return length;
> + } else if (length < 512) {
> + error_set(errp, ERROR_CLASS_GENERIC_ERROR,
> + "dmg file must be at least 512 bytes long");
> + return -EINVAL;Not worth respinning but error_setg() is a shortcut for error_set(errp, ERROR_CLASS_GENERIC_ERROR, fmt, ...). Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
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