Re: about kiobuf

[Christoph Hellwig <hch@caldera.de>]

On Fri, May 11, 2001 at 10:44:43AM +0100, petur thors wrote:
> HI
> 
> I have a few questions about the kiobuf architecture, specialy about the
> map_user_kiobuf routine:
> int map_user_kiobuf(int rw, struct kiobuf  *iobuf, unsigned long va, size_t
> len)
> I know that the ´va´ must be page-aligned but how can I determine the size_t
> len?
> Suppose this code is in mydriver_write() and the application programm sends
> in a char *user_buffer and I want to map the pages of the buffer and lock
> them down how can I determine the length of the user_buffer? Should I just
> put it to the maximun length of one kiobuf structure (64K)?
> The va parameter would be:
> addr = (unsigned long)user_buffer & PAGE_MASK;
> But what about size_t len?

static ssize_t
foo_write(struct file *fp, const char *bufp, size_t size, loff_t *offp)
					      ^^^^^^^^^

Hope that helps - a very good example that also does some rounding,
etc is drivers/char/raw.c.

	Christoph

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