Em 20-08-2012 05:30, Hans Verkuil escreveu: > Hi all! > > Recently I had to add two new ioctls for the subdev API (include/linux/v4l2-subdev.h) > and I noticed that the numbering of the ioctls was somewhat random. > > In most cases the ioctl number was the same as the V4L2 API counterpart, but for > subdev-specific ioctls no rule exists. > > There are a few problems with this: because of the lack of rules there is a chance > that in the future a subdev ioctl may end up to be identical to an existing V4L2 > ioctl. Also, because the numbering isn't nicely increasing it makes it hard to create > a lookup table as was done for the V4L2 ioctls. Well, you could do it, but it would > be a very sparse array, wasting a lot of memory. > > Lookup tables have proven to be very useful, so we might want to introduce them for > the subdev core code as well in the future. > > Since the subdev API is still marked experimental, I propose to renumber the ioctls > and use the letter 'v' instead of 'V'. 'v' was used for V4L1, and so it is now > available for reuse. 'v' is already used (mainly by fs): 'v' 00-1F linux/ext2_fs.h conflict! 'v' 00-1F linux/fs.h conflict! 'v' 00-0F linux/sonypi.h conflict! 'v' C0-FF linux/meye.h conflict! Reusing the ioctl numbering is a bad thing, as tracing code like strace will likely say that a different type of ioctl was called. (Yeah, unfortunately, this end by merging with duplicated stuff :< ) Also, I don't like the idea of deprecating it just because of that: interfaces are supposed to be stable. It should be noticed that there are very few ioctls there. So, using a lookup table is overkill. IMO, the better is to sort the ioctl's there at the header file, in order to avoid ioctl duplicaton. > We keep the old ioctls around for a few kernel cycles, and remove them some time > next year. > > Note that some V4L2 ioctls are also available for use in the subdev API (control > ioctls in particular). By using a different letter for the ioctls this will make > it easy as well to decide what lookup table to use should we decide to introduce > that in the subdev core code in the future. > > Comments? > > Regards, > > Hans > -- 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
