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SubjectRe: [patch] pipe: add support for shrinking and growing pipes
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.

--
Jens Axboe



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