Em 26-06-2011 15:20, Arnd Bergmann escreveu: > On Sunday 26 June 2011 19:30:46 Mauro Carvalho Chehab wrote: >>> There was a lot of debate whether undefined ioctls on non-ttys should >>> return -EINVAL or -ENOTTY, including mass-conversions from -ENOTTY to >>> -EINVAL at some point in the pre-git era, IIRC. >>> >>> Inside of v4l2, I believe this is handled by video_usercopy(), which >>> turns the driver's -ENOIOCTLCMD into -ENOTTY. What cases do you observe >>> where this is not done correctly and we do return ENOIOCTLCMD to >>> vfs_ioctl? >> >> Well, currently, it is returning -EINVAL maybe due to the mass-conversions >> you've mentioned. > > I mean what do you return *to* vfs_ioctl from v4l? The conversions must > have been long before we introduced compat_ioctl and ENOIOCTLCMD. > > As far as I can tell, video_ioctl2 has always converted ENOIOCTLCMD into > EINVAL, so changing the vfs functions would not have any effect. Yes. This discussion was originated by a RFC patch proposing to change video_ioctl2 to return -ENOIOCTLCMD instead of -EINVAL. >> The point is that -EINVAL has too many meanings at V4L. It currently can be >> either that an ioctl is not supported, or that one of the parameters had >> an invalid parameter. If the userspace can't distinguish between an unimplemented >> ioctl and an invalid parameter, it can't decide if it needs to fall back to >> some different methods of handling a V4L device. >> >> Maybe the answer would be to return -ENOTTY when an ioctl is not implemented. > > That is what a lot of subsystems do these days. But wouldn't that change > your ABI? Yes. The patch in question is also changing the DocBook spec for the ABI. We'll likely need to drop some notes about that at the features-to-be-removed.txt. I don't think that applications are relying at -EINVAL in order to detect if an ioctl is not supported, but before merging such patch, we need to double-check. Mauro. -- 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
