On Wed, Jan 07, 2015 at 03:19:13PM +0100, Peter Wu wrote:
> On Wednesday 07 January 2015 13:19:34 Stefan Hajnoczi wrote:
> > 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>
>
> Good to know, I got a compile error when ERROR_CLASS_GENERIC_ERROR was
> omitted, didn't think of using error_setg instead.
>
> When merging, please replace the above ERROR_CLASS_GENERIC_ERROR by:
>
> error_setg(errp, "dmg file must be at least 512 bytes long");
>
> (and likewise for the last error_set in the function)Done! Stefan
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