Re: [Q] vb2 userptr: struct vb2_ops::buf_cleanup() is called without buf_init()

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Hi Guennadi,

(CC'ing Pawel and Marek)

On Monday 21 May 2012 10:30:19 Guennadi Liakhovetski wrote:
> Hi
> 
> A recent report
> 
> http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/47594
> 
> has revealed the following asymmetry in how videobuf2 functions:
> 
> as is also documented in videobuf2-core.h, the user's struct
> vb2_ops::buf_init() method in the MMAP case is called after allocating the
> respective buffer, which happens at REQBUFS time, in the USERPTR case it
> is called after acquiring a new buffer at QBUF time. If the allocation in
> MMAP case fails, the respective buffer simply doesn't get created.
> However, if acquiring a new USERPTR buffer at QBUF time fails, the buffer
> object remains on the queue, but the user-provided .buf_init() method is
> not called for it. When the queue is destroyed, the user's .buf_cleanup()
> method is called on an uninitialised buffer. This is exactly the reason
> for the BUG() in the above referenced report.
> 
> Therefore my question: is this videobuf2-core behaviour really correct and
> we should be prepared in .buf_cleanup() to process uninitialised buffers,
> or should the videobuf2-core be adjusted?

>From a driver's point of view, it would make sense not to call .buf_cleanup() 
if .buf_init() hasn't been called. Otherwise each driver would need to check 
whether the buffer has been initialized, which would lead to code duplication.

A new buffer state would help tracking this in the vb2 core. I haven't tried 
to implement it though, so I might be underestimating the effort.

-- 
Regards,

Laurent Pinchart

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