Re: [RFC][2.5] generic_usercopy() function (resend, forgot the patches)

[Christoph Hellwig]

On Fri, May 23, 2003 at 12:10:57PM +0200, Michael Hunold wrote:
> > Also file/inode should go away from the prototype (and the callback).
> > Only file is needed because inode == file->f_dentry->d_inode, and even
> > that one should be just some void *data instead.
> 
> I only copied the function from videodev.c and renamed it, so please 
> don't blame me for the way stuff is done there. 8-)
> 
> Perhaps Gerd Knorr or Alan Cox can comment on your changes -- I'll have 
> to investigate if all of these arguments are used anyway.

I don't blame you.  I just think it shouldn't be added to the kernel API
without fixing it first :)

> 
> >>+	case _IOC_READ: /* some v4l ioctls are marked wrong ... */
> > That's crap.  Please move this workaround to v4l not into generic code.
> 
> Is it possible to fix the definitons of the v4l ioctls instead without 
> breaking binary compatiblity?

I doubt it.  This just means v4l has to work around it's bug in the
v4l code, not in common code.

> >>+	case _IOC_WRITE:
> >>+	case (_IOC_WRITE | _IOC_READ):
> >>+		if (_IOC_SIZE(cmd) <= sizeof(sbuf)) {
> >>+			parg = sbuf;
> >>+		} else {
> >>+			/* too big to allocate from stack */
> >>+			mbuf = kmalloc(_IOC_SIZE(cmd),GFP_KERNEL);
> >>+			if (NULL == mbuf)
> >>+				return -ENOMEM;
> >>+			parg = mbuf;
> > 
> > 
> > I wonder whether you should just kmalloc always. 
> 
> Since this function is always used in user context and the memory is 
> always freed afterwards, it should be possible to use vmalloc() or a 
> static buffer (what's the maximum size?) instead.

Sorry, I meant it's probably not worth using the stack at all.
vmalloc() for ioctl buffers sounds like a very bad idea.