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+.\" Copyright (c) 1995 Michael Chastain (mec@shell.portal.com), 15 April 1995.
+.\"
+.\" SPDX-License-Identifier: GPL-2.0-or-later
+.\"
+.\" 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 2023-03-30 "Linux man-pages 6.05.01"
+.SH NAME
+bdflush \- start, flush, or tune buffer-dirty-flush daemon
+.SH SYNOPSIS
+.nf
+.B #include <sys/kdaemon.h>
+.PP
+.BI "[[deprecated]] int bdflush(int " func ", long *" address );
+.BI "[[deprecated]] int bdflush(int " func ", long " data );
+.fi
+.SH DESCRIPTION
+.IR Note :
+Since Linux 2.6,
+.\" As noted in 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 STANDARDS
+Linux.
+.SH HISTORY
+Since glibc 2.23, glibc no longer supports this obsolete system call.
+.SH SEE ALSO
+.BR sync (1),
+.BR fsync (2),
+.BR sync (2)