.\" Copyright (c) 1995 Michael Chastain (mec@shell.portal.com), 15 April 1995.

.\"

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.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>

.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>

.\"

.TH BDFLUSH 2 2016-10-08 "Linux" "Linux Programmer's Manual"

.SH NAME

bdflush \- start, flush, or tune buffer-dirty-flush daemon

.SH SYNOPSIS

.nf

.B #include <sys/kdaemon.h>

.PP

.BI "int bdflush(int "  func ", long *" address );

.BI "int bdflush(int "  func ", long " data );

.fi

.SH DESCRIPTION

.IR Note :

Since Linux 2.6,

.\" As noted in a changes in the 2.5.12 source

this system call is deprecated and does nothing.

It is likely to disappear altogether in a future kernel release.

Nowadays, the task performed by

.BR bdflush ()

is handled by the kernel

.I pdflush

thread.

.PP

.BR bdflush ()

starts, flushes, or tunes the buffer-dirty-flush daemon.

Only a privileged process (one with the

.B CAP_SYS_ADMIN

capability) may call

.BR bdflush ().

.PP

If

.I func

is negative or 0, and no daemon has been started, then

.BR bdflush ()

enters the daemon code and never returns.

.PP

If

.I func

is 1,

some dirty buffers are written to disk.

.PP

If

.I func

is 2 or more and is even (low bit is 0), then

.I address

is the address of a long word,

and the tuning parameter numbered

.RI "(" "func" "\-2)/2"

is returned to the caller in that address.

.PP

If

.I func

is 3 or more and is odd (low bit is 1), then

.I data

is a long word,

and the kernel sets tuning parameter numbered

.RI "(" "func" "\-3)/2"

to that value.

.PP

The set of parameters, their values, and their valid ranges

are defined in the Linux kernel source file

.IR fs/buffer.c .

.SH RETURN VALUE

If

.I func

is negative or 0 and the daemon successfully starts,

.BR bdflush ()

never returns.

Otherwise, the return value is 0 on success and \-1 on failure, with

.I errno

set to indicate the error.

.SH ERRORS

.TP

.B EBUSY

An attempt was made to enter the daemon code after

another process has already entered.

.TP

.B EFAULT

.I address

points outside your accessible address space.

.TP

.B EINVAL

An attempt was made to read or write an invalid parameter number,

or to write an invalid value to a parameter.

.TP

.B EPERM

Caller does not have the

.B CAP_SYS_ADMIN

capability.

.SH VERSIONS

Since version 2.23, glibc no longer supports this obsolete system call.

.SH CONFORMING TO

.BR bdflush ()

is Linux-specific and should not be used in programs

intended to be portable.

.SH SEE ALSO

.BR sync (1),

.BR fsync (2),

.BR sync (2)

.SH COLOPHON

This page is part of release 4.15 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

\%https://www.kernel.org/doc/man\-pages/.