Re: [PATCH 1/2] vb2: Add VB2_FILEIO_ALLOW_ZERO_BYTESUSED flag to vb2_fileio_flags

[Hans Verkuil <hverkuil@xs4all.nl>]

On 02/18/15 10:42, Kamil Debski wrote:
> Hi Hans,
> 
>> From: Hans Verkuil [mailto:hverkuil@xs4all.nl]
>> Sent: Tuesday, February 17, 2015 10:11 AM
>>
>> Hi Kamil,
>>
>> On 12/16/14 12:36, Kamil Debski wrote:
>>> The vb2: fix bytesused == 0 handling (8a75ffb) patch changed the
>>> behavior of __fill_vb2_buffer function, so that if bytesused is 0 it
>>> is set to the size of the buffer. However, bytesused set to 0 is used
>>> by older codec drivers as as indication used to mark the end of
>> stream.
>>>
>>> To keep backward compatibility, this patch adds a flag passed to the
>>> vb2_queue_init function - VB2_FILEIO_ALLOW_ZERO_BYTESUSED. If the
>> flag
>>> is set upon initialization of the queue, the videobuf2 keeps the
>> value
>>> of bytesused intact and passes it to the driver.
>>
>> What is the status of this patch series?
> 
> I have to admit that I had forgotten a bit about this patch, because of
> other
> important work. Thanks for reminding me :)
>  
>> Note that io_flags is really the wrong place for this flag, it should
>> be io_modes. This flag has nothing to do with file I/O.
> 
> What do you think about adding a separate flags field into the vb2_queue
> structure? This could be combined with changing io_flags to u8 or a bit
> field
> to save space.

I think changing io_flags to a bitfield is a good idea.

	unsigned fileio_read_once:1;
	unsigned fileio_write_immediately:1;
	unsigned allow_zero_bytesused:1;

However, going back to allow_zero_bytesused: this has been broken for
quite some time without anyone complaining (other than you :-) ). Might
it not be better to just fix this properly by calling V4L2_DEC_CMD_STOP,
as done here: https://www.mail-archive.com/linux-media@vger.kernel.org/msg84916.html,
and drop the support for zero bytesused to mark EOS entirely?

I might be too optimistic here. Or perhaps at least add a pr_warn telling
users to switch to V4L2_DEC_CMD_STOP since this will be removed in 2017 or
whatever.

Regards,

	Hans