From: Michael Kerrisk on
On Sat, Jun 19, 2010 at 8:13 PM, Jens Axboe <jaxboe(a)fusionio.com> wrote:
> On 19/06/10 07.45, Michael Kerrisk wrote:
>> Hello Jens,
>>
>> I've tested this F_SETPIPE_SZ code as it appears in 2.6.35-rc3, and
>> things seem to work as advertised, if the text below is the correct
>> advertisement. Could you please review the following man-pages text,
>> and let me know if it's okay.
>>
>> fcntl.2:
>> � � � �F_SETPIPE_SZ (long; since Linux 2.6.35)
>> � � � � � � � Change �the �capacity of the pipe referred to by
>> � � � � � � � fd to be at least arg �bytes. � An �unprivileged
>> � � � � � � � process �can �adjust �the �pipe �capacity to any
>> � � � � � � � value between the system page size and the limit
>> � � � � � � � defined � in � /proc/sys/fs/pipe-size-max � (see
>> � � � � � � � proc(5)). �Attempts to �set �the �pipe �capacity
>> � � � � � � � below �the �page size are silently rounded up to
>> � � � � � � � the page size. �Attempts by an unprivileged pro-
>> � � � � � � � cess to set the pipe capacity above the limit in
>> � � � � � � � /proc/sys/fs/pipe-size-max � yield � the � error
>> � � � � � � � EPERM; �a �privileged process (CAP_SYS_RESOURCE)
>> � � � � � � � can override the �limit. � When �allocating �the
>> � � � � � � � buffer for the pipe, the kernel may use a capac-
>> � � � � � � � ity larger than arg, if that is �convenient �for
>> � � � � � � � the �implementation. �The F_GETPIPE_SZ operation
>> � � � � � � � returns the actual size used. �Attempting to set
>> � � � � � � � the �pipe �capacity �smaller �than the amount of
>> � � � � � � � buffer space currently used to store �data �pro-
>> � � � � � � � duces the error EBUSY.
>>
>> � � � �F_GETPIPE_SZ (void; since Linux 2.6.35)
>> � � � � � � � Return �(as the function result) the capacity of
>> � � � � � � � the pipe referred to by fd.
>>
>> And in proc.5:
>> � � � �/proc/sys/fs/pipe-max-size (since Linux 2.6.35)
>> � � � � � � � The value in this file defines �an �upper �limit
>> � � � � � � � for �raising �the �capacity �of a pipe using the
>> � � � � � � � fcntl(2) �F_SETPIPE_SZ �operation. � This �limit
>> � � � � � � � applies �only �to �unprivileged �processes. �The
>> � � � � � � � default value for this file is �1,048,576. � The
>> � � � � � � � value �assigned �to �this �file �may �be rounded
>> � � � � � � � upward, to reflect the value �actually �employed
>> � � � � � � � for �a �convenient implementation. �To determine
>> � � � � � � � the rounded-up value, display �the �contents �of
>> � � � � � � � this �file �after �assigning a value to it. �The
>> � � � � � � � minimum value that can be assigned to this �file
>> � � � � � � � is the system page size.
>
> Looks good to me.

Thanks!

Cheers,

Michael


--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface" http://blog.man7.org/
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