On Fri, 2011-06-24 at 19:16 -0300, Mauro Carvalho Chehab wrote: > Em 24-06-2011 18:04, Andy Walls escreveu: > > On Fri, 2011-06-24 at 14:48 -0400, Devin Heitmueller wrote: > >> On Fri, Jun 24, 2011 at 2:34 PM, Stefan Richter > >> <stefanr@xxxxxxxxxxxxxxxxx> wrote: > >>> If the "driver version" is in fact an ABI version, then the driver author > >>> should really increase it only when ABI behavior is changed (and only if > >>> the behavior change can only be communicated by version number --- e.g. > >>> addition of an ioctl is not among such reasons). And the author should > >>> commit behavior changing implementation and version number change in a > >>> single changeset. > >>> > >>> And anybody who backmerges such an ABI behavior change into another kernel > >>> branch (stable, longterm, distro...) must backmerge the associated version > >>> number change too. > >>> > >>> Of course sometimes people realize this only after the fact. Or driver > >>> authors don't have a clear understanding of ABI versioning to begin with. > >>> I am saying so because I had to learn it too; I certainly wasn't born > >>> with an instinct knowledge how to do it properly. > >>> > >>> (Disclaimer: I have no stake in drivers/media/ ABIs. But I am involved > >>> in maintaining a userspace ABI elsewhere in drivers/firewire/, and one of > >>> the userspace libraries that use this ABI.) > >> > >> Hi Stefan, > >> > >> To be clear, I don't think anyone is actually proposing that the > >> driver version number really be used as any form of formal "ABI > >> versioning" scheme. In almost all cases, it's so the application can > >> know to *not* do something is the driver is older than X. > > > > MythTV, for example, used to use the driver version to work around old > > VBI bugs and MPEG encoder quirks that the older version of the driver > > may not have known how to handle: > > > > https://github.com/MythTV/mythtv/blob/b98d3a98e3187000ae652df5ffebe2beb5221ba7/mythtv/libs/libmythtv/mpegrecorder.cpp#L335 > > > > But for newer versions, MythTV could avoid using its own odd hacks. > > The bleeding edge MythTV now has most of these removed. > > Removing it is a good thing. > > >> Really, this is all about applications being able to jam a hack into > >> their code that translates to "don't call this ioctl() with some > >> particular argument if it's driver W less than version X, because the > >> driver had a bug that is likely to panic the guy's PC". > > > > Well, not even panics per se, but some thing like the VBI is broken, or > > the volume control doesn't work, IR blaster is works for this version, > > or something else stupid that is very visible to the end user. > > > > I also use the driver version for troubleshooting problem with users. I > > roughly know what wasn't working in what version of the cx18 and ivtv > > drivers. If the end user can tell me the driver version (using v4l2-ctl > > --log-status) along with his symptoms, it makes my life easier. Being > > able to efficiently help the end user is a win for both me and the end > > user. > > If you add it to MODULE_VERSION, you can get the version with: > > $ modinfo -F version vivi > 0.8.1 Well, since you mention it.... http://git.linuxtv.org/media_tree.git?a=blob;f=drivers/media/video/cx18/cx18-driver.c;h=9e2f870f4258665ae6093c762f752d45147a8c98;hb=staging/for_v3.1#l252 http://git.linuxtv.org/media_tree.git?a=blob;f=drivers/media/video/ivtv/ivtv-driver.c;h=0fb75524484d909af4925c3c33c9f12cf6d6519e;hb=staging/for_v3.1#l280 However, since I often must ask for the output of v4l2-ctl --log-status, which already has the version number, I never need to ask the user to run /sbin/modinfo for the version. Regards, Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
