Re: ulimit -p incorrect on linux (and besides being low, probably unenforceable(?))

[Chet Ramey]

Linda Walsh wrote:
> Chet Ramey wrote:
>> Linda Walsh wrote:
>>> When under linux (2.6.30.x), I type
>>> ulimit -p and get a return value of "8".
>>>
>>> from the man page this is in 512-byte blocks and may not be set.
>>
>> It's set at build time.  Look at builtins/ulimit.def:pipesize() and
>> builtins/psize.sh (which uses builtins/psize.c).
>> Chet
> ----
>     What is supposed to be controlling?
> 
>     When I create a pipe with the pipe system call, and try writing
> blocks of data from a master(parent) to a child, I get very large values
> for
> bytes sent in one write or read in one read from the pipe.
> 
>     More like it's a limitation on some physical memory constraint.

No, it's the atomic pipe size.  That's the number of bytes guaranteed to
be written to a pipe atomically (as a single unit, without interspersing
data from other processes).  This is 4096 on Linux no matter how you get
it:

PIPE_BUF/pathconf/fpathconf/sysconf/getconf/write-and-run-your-own-program.

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer

Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/