On Mon, 12 Apr 2021 13:44:45 +0200, Jaroslav Kysela wrote:
Dne 12. 04. 21 v 13:17 Takashi Iwai napsal(a):
In this case, we have 31 free bits and this information can be stored there. I would prefer to keep the reserved bytes for some large fields.
Again, C language doesn't define the position of the bit fields. That's the primary problem.
Yes and no. It seems that it's not a big C compiler implementation problem, because other drivers are using the bitfields in the uapi structures, too. Yes, it may need some extra care.
Right, and the need for care is mostly for little merit -- that's the point. I'm not against about the bit flags at all, but pointing that the C bit fields are too error-prone for ioctl structs.
If we really have to save the space, it's a nice workaround. But for other purposes, there is really little merit and more flip side by that.
I see your reluctance to talk about extension of the bit field word, but perhaps, we may be clever and define the flag word for the newly added parameters now. The space may be used more precisely in the future with this change.
Sure, that pattern is common and recommended for bit-wise flags.
thanks,
Takashi