[PATCH 4/5] Update linux/ioctlent.h.in file

[Dmitry V. Levin]

On Fri, Jan 16, 2015 at 09:49:19AM +0100, Gabriel Laskar wrote:
> On Fri, Jan 16, 2015 at 12:39 AM, Dmitry V. Levin wrote:
[...]
> > strace uses only 16 bits (8-bit number and 8-bit type) of the 32-bit ioctl
> > command, so the only real solution to this issue is to take into account
> > remaining 16 bits (size and direction).
> >
> > For example,
> > SNDCTL_TMR_TIMEBASE is _IOC(_IOC_READ|_IOC_WRITE, 'T', 1, sizeof(int)),
> > SNDRV_TIMER_IOCTL_NEXT_DEVICE is _IOC(_IOC_READ|_IOC_WRITE, 'T', 1, sizeof(struct snd_timer_id)),
> > TCGETS is architecture-specific, its generic value 0x5401 is _IOC(0, 'T', 1, 0).
> >
> > As you can see all these 32-bit values are different.
> > The only question is how to evaluate these remaining bits reliably, especially
> > 14 bits (or 13 on alpha, mips, powerpc, and sparc) of ioctl command size.
> 
> Or we could do that, yes. I don't know why I have occulted this
> solution. I have missed the 14/13 bit snafu though.
> 
> Maybe we can create 2 ioctlent.h.in files, 1 for the 14 bits size, and
> another one for the 13 bits one and compile the right one for each
> arch.

If we succeeded to fetch the "size" bits, we could avoid these
architecture-specific complications by storing {dir,type,nr,size}
in ioctlent.h.in files apart, and assembling them into 32-bit words
at build time.
This way we won't need two different generic ioctlent.h.in files.

We still have to support small architecture-specific ioctlent.h.in
files because some historic ioctl commands like TCGETS differ.


-- 
ldv
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