On Sun, Dec 11, 2016 at 01:54:28PM +0100, wm4 wrote:
> On Sat, 10 Dec 2016 23:01:04 +0100
> Michael Niedermayer <mich...@niedermayer.cc> wrote:
>
> > When we will backport this, it will be inevitably in a different location
> > in AVCodecContext in each release and master. 3.0, 3.1, 3.2 and master
> > use the same soname though and must have a binary compatible interface.
> > It thus can only saftely be accessed through AVOptions
> >
> > It may be enough to require this only in the releases but that could be
> > rather confusing.
> >
> > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc>
> > ---
> > libavcodec/avcodec.h | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> > index 02234aee67..8123092ac0 100644
> > --- a/libavcodec/avcodec.h
> > +++ b/libavcodec/avcodec.h
> > @@ -3573,8 +3573,8 @@ typedef struct AVCodecContext {
> > /**
> > * The number of pixels per image to maximally accept.
> > *
> > - * - decoding: set by user
> > - * - encoding: set by user
> > + * - decoding: set by user through AVOptions (NO direct access)
> > + * - encoding: set by user through AVOptions (NO direct access)
> > */
> > int64_t max_pixels;
> >
>
> Why? We gave up the Libav ABI compat. abomination.Its explained in the patch comment above max_pixels should to be backported as it allows users to control memory use from large images better, avoid some OOMs and fixes issues which some people consider security bugs if its backported it will not be in the same location relative to the start of AVCodecContext in master, 3.2, 3.1, 3.0 master, 3.2, 3.1, 3.0 all have the same soname libs using the same soname need to be binary compatible direct access to one location will not work and thus be binary incompatible if the field is at a different location Thus releases cannot use direct access to the max_pixels field. One could say it differently in that if 3.0.X would access max_pixels directly at byte offset 123 then an application built against that and linked to 3.2 will access another field before max_pixels in 3.2 AVOptions solves that corner case of backporting added fields. This restriction can simply be droped on the next ABI major bump [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Its not that you shouldnt use gotos but rather that you should write readable code and code with gotos often but not always is less readable
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