mirror of https://github.com/mkerrisk/man-pages
128 lines
3.4 KiB
Groff
128 lines
3.4 KiB
Groff
.\" Copyright (c) 1995 Michael Chastain (mec@shell.portal.com), 15 April 1995.
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.\"
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.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, see
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.\" <http://www.gnu.org/licenses/>.
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.\" %%%LICENSE_END
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.\"
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.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
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.\" Modified 2004-06-17 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.TH BDFLUSH 2 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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bdflush \- start, flush, or tune buffer-dirty-flush daemon
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.SH SYNOPSIS
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.nf
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.B #include <sys/kdaemon.h>
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.PP
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.BI "int bdflush(int " func ", long *" address );
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.BI "int bdflush(int " func ", long " data );
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.fi
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.PP
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.IR Note :
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There is no glibc wrapper for this system call; see VERSIONS.
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.SH DESCRIPTION
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.IR Note :
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Since Linux 2.6,
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.\" As noted in changes in the 2.5.12 source
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this system call is deprecated and does nothing.
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It is likely to disappear altogether in a future kernel release.
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Nowadays, the task performed by
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.BR bdflush ()
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is handled by the kernel
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.I pdflush
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thread.
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.PP
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.BR bdflush ()
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starts, flushes, or tunes the buffer-dirty-flush daemon.
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Only a privileged process (one with the
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.B CAP_SYS_ADMIN
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capability) may call
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.BR bdflush ().
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.PP
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If
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.I func
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is negative or 0, and no daemon has been started, then
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.BR bdflush ()
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enters the daemon code and never returns.
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.PP
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If
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.I func
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is 1,
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some dirty buffers are written to disk.
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.PP
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If
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.I func
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is 2 or more and is even (low bit is 0), then
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.I address
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is the address of a long word,
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and the tuning parameter numbered
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.RI "(" "func" "\-2)/2"
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is returned to the caller in that address.
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.PP
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If
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.I func
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is 3 or more and is odd (low bit is 1), then
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.I data
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is a long word,
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and the kernel sets tuning parameter numbered
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.RI "(" "func" "\-3)/2"
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to that value.
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.PP
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The set of parameters, their values, and their valid ranges
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are defined in the Linux kernel source file
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.IR fs/buffer.c .
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.SH RETURN VALUE
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If
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.I func
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is negative or 0 and the daemon successfully starts,
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.BR bdflush ()
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never returns.
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Otherwise, the return value is 0 on success and \-1 on failure, with
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.I errno
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set to indicate the error.
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.SH ERRORS
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.TP
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.B EBUSY
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An attempt was made to enter the daemon code after
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another process has already entered.
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.TP
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.B EFAULT
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.I address
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points outside your accessible address space.
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.TP
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.B EINVAL
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An attempt was made to read or write an invalid parameter number,
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or to write an invalid value to a parameter.
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.TP
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.B EPERM
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Caller does not have the
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.B CAP_SYS_ADMIN
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capability.
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.SH VERSIONS
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Since version 2.23, glibc no longer supports this obsolete system call.
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.SH CONFORMING TO
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.BR bdflush ()
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is Linux-specific and should not be used in programs
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intended to be portable.
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.SH SEE ALSO
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.BR sync (1),
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.BR fsync (2),
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.BR sync (2)
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