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fcntl.2: Document F_SETPIPE_SZ and F_GETPIPE_SZ 

These commands, new in kernel 2.6.35, set and get the capacity
of pipes.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2010-06-17 00:11:47 +02:00
parent 23a05d28b6
commit 14f7d1a4bd
1 changed files with 38 additions and 1 deletions
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@ -4,7 +4,7 @@
.\" This manpage is Copyright (C) 1992 Drew Eckhardt;
.\" and Copyright (C) 1993 Michael Haardt, Ian Jackson;
.\" and Copyright (C) 1998 Jamie Lokier;
.\" and Copyright (C) 2002 Michael Kerrisk.
.\" and Copyright (C) 2002-2010 Michael Kerrisk.
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
@ -55,6 +55,8 @@
.\" 2009-09-30, Michael Kerrisk
.\" Note obsolete F_SETOWN behavior with threads.
.\" Document F_SETOWN_EX and F_GETOWN_EX
.\" 2010-06-17, Michael Kerrisk
.\" Document F_SETPIPE_SZ and F_GETPIPE_SZ.
.\"
.TH FCNTL 2 2010-06-17 "Linux" "Linux Programmer's Manual"
.SH NAME
@ -998,6 +1000,36 @@ which provides a much superior interface for obtaining notifications of
file system events.
See
.BR inotify (7).
.SS "Changing the capacity of a pipe"
.TP
.BR F_SETPIPE_SZ " (\fIlong\fP; since Linux 2.6.35)"
Change the capacity of the pipe referred to by
.I fd
to be at least
.I arg
bytes.
An unprivileged process can adjust the pipe capacity to any value
between the system page size and the limit defined in
.IR /proc/sys/fs/pipe-size-max
(see
.BR proc (5));
a privileged process
.RB ( CAP_SYS_RESOURCE )
can override the limit.
When allocating the buffer for the pipe,
the kernel may use a capacity larger than
.IR arg ,
if that is convenient for the implementation.
The
.B 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 produces the error
.BR EBUSY .
.TP
.BR F_GETPIPE_SZ " (\fIvoid\fP; since Linux 2.6.35)"
Return (as the function result) the capacity of the pipe referred to by
.IR fd .
.SH "RETURN VALUE"
For a successful call, the return value depends on the operation:
.TP 0.9i
@ -1022,6 +1054,9 @@ for traditional
.B SIGIO
behavior.
.TP
.B F_GETPIPE_SZ
The pipe capacity.
.TP
All other commands
Zero.
.PP
@ -1111,6 +1146,8 @@ is specified in POSIX.1-2008.
.BR F_GETOWN_EX ,
.BR F_SETOWN_EX ,
.BR F_SETPIPE_SZ ,
.BR F_GETPIPE_SZ ,
.BR F_GETSIG ,
.BR F_SETSIG ,
.BR F_NOTIFY ,