Re: limits / PIPE_BUF?

[Arjan van de Ven <arjan@infradead.org>]

On Thu, 2006-05-04 at 10:50 -0700, Vadim Lobanov wrote:
> On Thu, 4 May 2006, Arjan van de Ven wrote:
> 
> > On Thu, 2006-05-04 at 09:39 -0700, Vadim Lobanov wrote:
> > > How does the kernel
> > > code ensure that this value is honored, considering that PIPE_BUF is
> > > not
> > > referenced in any of the pipe code?
> >
> >
> > the kernel implementation guarantees one page basically, and on all
> > architectures that I know of that's at least 4096 bytes
> >
> 
> Alright, so sounds like this constant should remain inside the
> include/linux/limits.h file. What about #defining it to be equal to
> PAGE_SIZE, like ARM (include/linux-arm/limits.h, for example) does?

there is a certain elegance in providing the same value on all
architectures; it means apps don't suddenly break if you port it to 
a "lesser" one. Also there is a problem with PAGE_SIZE itself, that's a
config option on several architectures, so it'd have to be a define for
get_page_size() or something, at which point you change semantics since
apps can't do

char foo[PIPE_BUF];

anymore