[PATCH 01/27] libcamera: MappedFrameBuffer: Add tracking of mmap file descriptors to MappedFrameBuffer

[Laurent Pinchart]

On Wed, Apr 23, 2025 at 10:35:12AM +0100, Kieran Bingham wrote:
> Quoting Bryan O'Donoghue (2025-04-22 22:58:54)
> > In order to import via eglCreateImageKHR via an file descriptor we need to
> > have access to the file descriptor associated with the plane.
> > 
> > Extend MappedFrameBuffer to track the file descriptor giving an accessor
> > method in-line with the existing planes_ accessor.
> 
> I expect the answers are later in the series, but I would expect if you
> need the file descriptors - you should get them from the FrameBuffer
> directly, not the 'MappedFrameBuffer' otherwise you're just making a
> copy of something you already have to be able to access it ? (It could
> be fine - but depends on what the use case is)

Storing them here as plain integers opens the door to use-after-free. I
also expect answers later in the series, let's see if we can make the
code harder to use incorrectly.

> > Signed-off-by: Bryan O'Donoghue <bryan.odonoghue at linaro.org>
> > ---
> >  include/libcamera/internal/mapped_framebuffer.h | 2 ++
> >  src/libcamera/mapped_framebuffer.cpp            | 1 +
> >  2 files changed, 3 insertions(+)
> > 
> > diff --git a/include/libcamera/internal/mapped_framebuffer.h b/include/libcamera/internal/mapped_framebuffer.h
> > index 6aaabf50..cb81243e 100644
> > --- a/include/libcamera/internal/mapped_framebuffer.h
> > +++ b/include/libcamera/internal/mapped_framebuffer.h
> > @@ -31,6 +31,7 @@ public:
> >         bool isValid() const { return error_ == 0; }
> >         int error() const { return error_; }
> >         const std::vector<Plane> &planes() const { return planes_; }
> > +       const std::vector<int> &fds() const { return fds_; }
> >  
> >  protected:
> >         MappedBuffer();
> > @@ -38,6 +39,7 @@ protected:
> >         int error_;
> >         std::vector<Plane> planes_;
> >         std::vector<Plane> maps_;
> > +       std::vector<int> fds_;
> >  
> >  private:
> >         LIBCAMERA_DISABLE_COPY(MappedBuffer)
> > diff --git a/src/libcamera/mapped_framebuffer.cpp b/src/libcamera/mapped_framebuffer.cpp
> > index f54bbf21..82ab132c 100644
> > --- a/src/libcamera/mapped_framebuffer.cpp
> > +++ b/src/libcamera/mapped_framebuffer.cpp
> > @@ -237,6 +237,7 @@ MappedFrameBuffer::MappedFrameBuffer(const FrameBuffer *buffer, MapFlags flags)
> >                 }
> >  
> >                 planes_.emplace_back(info.address + plane.offset, plane.length);
> > +               fds_.emplace_back(fd);
> >         }
> >  }
> >  

-- 
Regards,

Laurent Pinchart