-.\" Hey Emacs! This file is -*- nroff -*- source.
-.\"
.\" Copyright 2003 Abhijit Menon-Sen <ams@wiw.org>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
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.\" 2005-04-08 mtk, noted kernel version and added BUGS
.\" 2010-10-09, mtk, document arm_fadvise64_64()
.\"
-.TH POSIX_FADVISE 2 2010-10-09 "Linux" "Linux Programmer's Manual"
+.TH POSIX_FADVISE 2 2014-12-31 "Linux" "Linux Programmer's Manual"
.SH NAME
posix_fadvise \- predeclare an access pattern for file data
.SH SYNOPSIS
The \fIadvice\fP applies to a (not necessarily existent) region starting
at \fIoffset\fP and extending for \fIlen\fP bytes (or until the end of
the file if \fIlen\fP is 0) within the file referred to by \fIfd\fP.
-The advice is not binding; it merely constitutes an expectation on behalf of
+The \fIadvice\fP is not binding;
+it merely constitutes an expectation on behalf of
the application.
Permissible values for \fIadvice\fP include:
.TP
.B POSIX_FADV_DONTNEED
The specified data will not be accessed in the near future.
-.SH "RETURN VALUE"
+.SH RETURN VALUE
On success, zero is returned.
On error, an error number is returned.
.SH ERRORS
.TP
.B ESPIPE
The specified file descriptor refers to a pipe or FIFO.
-(Linux actually
-returns
+.RB ( ESPIPE
+is the error specified by POSIX,
+but before kernel version 2.16,
+.\" commit 87ba81dba431232548ce29d5d224115d0c2355ac
+Linux returned
.B EINVAL
in this case.)
.SH VERSIONS
Library support has been provided since glibc version 2.2,
via the wrapper function
.BR posix_fadvise ().
-.SH "CONFORMING TO"
+
+Since Linux 3.18,
+.\" commit d3ac21cacc24790eb45d735769f35753f5b56ceb
+support for the underlying system call is optional,
+depending on the setting of the
+.B CONFIG_ADVISE_SYSCALLS
+configuration option.
+.SH CONFORMING TO
POSIX.1-2001.
Note that the type of the
.I len
that has already been used, so that more useful cached pages are not
discarded instead.
+Requests to discard partial pages are ignored.
+It is preferable to preserve needed data than discard unneeded data.
+If the application requires that data be considered for discarding then
+.I offset
+and
+.I len
+must be page-aligned.
+
Pages that have not yet been written out will be unaffected, so if the
application wishes to guarantee that pages will be released, it should
call
or
.BR fdatasync (2)
first.
-.SS arm_fadvise()
-The ARM architecture
-needs 64-bit arguments to be aligned in a suitable pair of registers.
-On this architecture, the call signature of
+.SS Architecture-specific variants
+Some architectures require
+64-bit arguments to be aligned in a suitable pair of registers (see
+.BR syscall (2)
+for further detail).
+On such architectures, the call signature of
.BR posix_fadvise ()
-is flawed, since it forces a register to be wasted as padding between the
+shown in the SYNOPSIS would force
+a register to be wasted as padding between the
.I fd
and
-.I len
+.I offset
arguments.
-Therefore, since Linux 2.6.14, ARM defines a different
-system call that orders the arguments suitably:
+Therefore, these architectures define a version of the
+system call that orders the arguments suitably,
+but otherwise is otherwise exactly the same as
+.BR posix_fadvise ().
+
+For example, since Linux 2.6.14, ARM has the following system call:
.PP
.in +4n
.nf
.BI "long arm_fadvise64_64(int " fd ", int " advice ,
-.BI " loff_t " offset ", loff_t " len );
+.BI " loff_t " offset ", loff_t " len );
.fi
.in
.PP
-The behavior of this system call is otherwise exactly the same as
-.BR posix_fadvise().
-No library support is provided for this system call in glibc.
-.\" No ARM support in glibc.
+These architecture-specific details are generally
+hidden from applications by the glibc
+.BR posix_fadvise ()
+wrapper function,
+which invokes the appropriate architecture-specific system call.
.SH BUGS
In kernels before 2.6.6, if
.I len
was specified as 0, then this was interpreted literally as "zero bytes",
rather than as meaning "all bytes through to the end of the file".
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR readahead (2),
.BR sync_file_range (2),
.BR posix_fallocate (3),
.BR posix_madvise (3)
.\" FIXME . Write a posix_fadvise(3) page.
+.SH COLOPHON
+This page is part of release 3.79 of the Linux
+.I man-pages
+project.
+A description of the project,
+information about reporting bugs,
+and the latest version of this page,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.
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