Re: limits / PIPE_BUF?

[Vadim Lobanov <vlobanov@speakeasy.net>]

On Thu, 4 May 2006, Arjan van de Ven wrote:

> On Wed, 2006-05-03 at 22:55 -0700, Vadim Lobanov wrote:
> > A snippet from include/linux/limits.h:
> > #define PIPE_BUF        4096    /* # bytes in atomic write to a pipe */
> >
> > PIPE_BUF is a bit of an oddity. It is defined there, then redefined in
> > the arm header files, even though those header files are never included
> > anywhere. Also, PIPE_BUF is never referenced by name in any of the Linux
> > code. And yet, it is still being mentioned in some Big And Scary
> > Warnings (tm): fs/autofs4/waitq.c or include/linux/pipe_fs_i.h, for
> > example.
>
> it's for userland to tell it what the size of the atomic pipe operations
> we can do is.
>

How does userland get this value from the kernel? How does the kernel
code ensure that this value is honored, considering that PIPE_BUF is not
referenced in any of the pipe code?

- Vadim Lobanov