On Tue, 2010-04-06 at 08:37 +0200, Hans Verkuil wrote: > On Tuesday 06 April 2010 00:12:48 Hans Verkuil wrote: > > On Monday 05 April 2010 23:47:10 Hans Verkuil wrote:
> > One thing that might be useful is to prefix the name with the control class > > name. E.g. hue becomes user_hue and audio_crc becomes mpeg_audio_crc. It > > would > > groups them better. Or one could make a controls/user and controls/mpeg > > directory. That might not be such a bad idea actually. > > Replying to your own mails is probably a bad sign, but I can't help myself :-) I had an old InfoCom text adventure game that would respond to querying oneself with: "Talking to oneself is a sign of impending mental collapse." :D > I've changed the code to add a control class prefix for all but the user > controls. > It looks much better now: > > $ ls /sys/class/video4linux/video1/controls > balance mpeg_insert_navigation_packets > mpeg_video_aspect > brightness mpeg_median_chroma_filter_maximum > mpeg_video_b_frames > chroma_agc mpeg_median_chroma_filter_minimum > mpeg_video_bitrate > chroma_gain mpeg_median_filter_type > mpeg_video_bitrate_mode > contrast mpeg_median_luma_filter_maximum > mpeg_video_encoding > hue mpeg_median_luma_filter_minimum > mpeg_video_gop_closure > mpeg_audio_crc mpeg_spatial_chroma_filter_type > mpeg_video_gop_size > mpeg_audio_emphasis mpeg_spatial_filter > mpeg_video_mute > mpeg_audio_encoding mpeg_spatial_filter_mode > mpeg_video_mute_yuv > mpeg_audio_layer_ii_bitrate mpeg_spatial_luma_filter_type > mpeg_video_peak_bitrate > mpeg_audio_mute mpeg_stream_type > mpeg_video_temporal_decimation > mpeg_audio_sampling_frequency mpeg_stream_vbi_format mute > mpeg_audio_stereo_mode mpeg_temporal_filter > saturation > mpeg_audio_stereo_mode_extension mpeg_temporal_filter_mode volume So this is beginning to look OK. You'll have longer names when a class name is longer than 4 characters (e.g. "technician_" ). However, I suppose it is better than another directory which creates a deeper hierarchy while still not avoiding the longer pathname. > > > One of the few drivers that exposes controls in sysfs is pvrusb2. As far > > > as > > > I can tell from the source it will create subdirectories under the device > > > node for each control. Those subdirs have the name ctl_<control-name> > > > (e.g. > > > ctl_volume), and below that are files exposing all the attributes of that > > > control: name, type, min_val, max_val, def_val, cur_val, custom_val, > > > enum_val > > > and bit_val. Most are clear, but some are a bit more obscure. enum_val is > > > basically a QUERYMENU and returns all menu options. bit_val seems to be > > > used > > > for some non-control values like the TV standard that pvrusb2 also exposes > > > and where bit_val is a bit mask of all the valid bits that can be used. > > > > > > Mike, if you have any additional information, just let us know. My pvrusb2 > > > is in another country at the moment so I can't do any testing. > > > > > > Personally I think that it is overkill to basically expose the whole > > > QUERYCTRL information to sysfs. I see it as an easy and quick way to read > > > and > > > modify controls via a command line. > > An in between solution would be to add _type files. So you would have 'hue' > > and > > 'hue_type'. 'cat hue_type' would give something like: > > If we go for something like this, then I think it would be better to make a > new subdirectory. So 'controls' just has the controls, and 'ctrl_info' or > something similar would have read-only files containing this information. sysfs' major usability problem for humans is the insane directory depths it can reach and the cross-links to everywhere. Humans attempt to keep a mental model of "where" they are in a logical "space", and sysfs is like "maze of twisty little passages, all alike". In the true sysfs spirit you should create a 'ctrl_info' directory full of nodes with metadata *and* also create "foo_type" symlinks to all of those metadata nodes. Bonus points for having the 'ctrl_info' directory and 'foo_type' symlinks in a different part of the sysfs tree but with a similar directory name. > Again, I still don't know whether we should do this. It is dangerously > seductive because it would be so trivial to implement. It's like watching ships run aground on a shallow sandbar that all the locals know about. The waters off of 'Point /sys' are full of usability shipwrecks. I don't know if it's some siren's song, the lack of a light house, or just strange currents that deceive even seasoned navigators.... Let the user run 'v4l2-ctl -d /dev/videoN -L' to learn about the control metatdata. It's not as easy as typing 'cat', but the user base using sysfs in an interactive shell or shell script should also know how to use v4l2-ctl. In embedded systems, the final system deployment should not need the control metadata available from sysfs in a command shell anyway. Regards, Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
