2004-11-03 13:51:07 +00:00
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.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright 2003 Abhijit Menon-Sen <ams@wiw.org>
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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2007-04-12 22:42:49 +00:00
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.\"
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2004-11-03 13:51:07 +00:00
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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2007-04-12 22:42:49 +00:00
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.\"
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2004-11-03 13:51:07 +00:00
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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2005-04-11 15:04:27 +00:00
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.\" 2005-04-08 mtk, noted kernel version and added BUGS
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2010-10-09 04:50:38 +00:00
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.\" 2010-10-09, mtk, document arm_fadvise64_64()
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2005-04-11 15:04:27 +00:00
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.\"
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2010-10-09 04:45:26 +00:00
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.TH POSIX_FADVISE 2 2010-10-09 "Linux" "Linux Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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.SH NAME
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posix_fadvise \- predeclare an access pattern for file data
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.SH SYNOPSIS
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.nf
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.B #include <fcntl.h>
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.sp
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2008-07-06 14:54:26 +00:00
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.BI "int posix_fadvise(int " fd ", off_t " offset ", off_t " len \
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", int " advice ");"
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2004-11-03 13:51:07 +00:00
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.fi
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2010-09-19 16:32:23 +00:00
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.sp
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.ad l
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.BR posix_fadvise ():
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.RS 4
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_XOPEN_SOURCE\ >=\ 600 || _POSIX_C_SOURCE\ >=\ 200112L
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.RE
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.ad
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.SH DESCRIPTION
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2007-05-12 09:06:04 +00:00
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Programs can use
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.BR posix_fadvise ()
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to announce an intention to access
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file data in a specific pattern in the future, thus allowing the kernel
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2007-06-08 09:56:56 +00:00
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to perform appropriate optimizations.
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2004-11-03 13:51:07 +00:00
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The \fIadvice\fP applies to a (not necessarily existent) region starting
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at \fIoffset\fP and extending for \fIlen\fP bytes (or until the end of
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2007-04-12 22:42:49 +00:00
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the file if \fIlen\fP is 0) within the file referred to by \fIfd\fP.
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2011-09-08 14:11:32 +00:00
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The \fIadvice\fP is not binding;
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it merely constitutes an expectation on behalf of
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the application.
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Permissible values for \fIadvice\fP include:
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.TP
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.B POSIX_FADV_NORMAL
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Indicates that the application has no advice to give about its access
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2007-04-12 22:42:49 +00:00
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pattern for the specified data.
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If no advice is given for an open file,
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this is the default assumption.
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.TP
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.B POSIX_FADV_SEQUENTIAL
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The application expects to access the specified data sequentially (with
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lower offsets read before higher ones).
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.TP
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.B POSIX_FADV_RANDOM
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The specified data will be accessed in random order.
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.TP
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.B POSIX_FADV_NOREUSE
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The specified data will be accessed only once.
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.TP
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.B POSIX_FADV_WILLNEED
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The specified data will be accessed in the near future.
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.TP
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.B POSIX_FADV_DONTNEED
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The specified data will not be accessed in the near future.
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.SH "RETURN VALUE"
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On success, zero is returned.
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On error, an error number is returned.
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.SH ERRORS
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.TP
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.B EBADF
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The \fIfd\fP argument was not a valid file descriptor.
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.TP
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.B EINVAL
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An invalid value was specified for \fIadvice\fP.
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.TP
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.B ESPIPE
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2007-06-22 17:16:20 +00:00
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The specified file descriptor refers to a pipe or FIFO.
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(Linux actually
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returns
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.B EINVAL
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in this case.)
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2007-05-18 16:06:42 +00:00
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.SH VERSIONS
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2010-10-09 04:45:26 +00:00
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Kernel support first appeared in Linux 2.5.60;
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the underlying system call is called
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.BR fadvise64 ().
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.\" of fadvise64_64()
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Library support has been provided since glibc version 2.2,
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via the wrapper function
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.BR posix_fadvise ().
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2007-05-18 16:06:42 +00:00
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.SH "CONFORMING TO"
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POSIX.1-2001.
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Note that the type of the
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.I len
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argument was changed from
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.I size_t
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to
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.I off_t
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in POSIX.1-2003 TC1.
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.SH NOTES
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Under Linux, \fBPOSIX_FADV_NORMAL\fP sets the readahead window to the
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default size for the backing device; \fBPOSIX_FADV_SEQUENTIAL\fP doubles
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this size, and \fBPOSIX_FADV_RANDOM\fP disables file readahead entirely.
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2005-07-05 13:50:51 +00:00
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These changes affect the entire file, not just the specified region
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(but other open file handles to the same file are unaffected).
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2006-09-26 12:41:08 +00:00
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\fBPOSIX_FADV_WILLNEED\fP initiates a
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accept.2, connect.2, eventfd.2, flock.2, open.2, posix_fadvise.2, read.2, recv.2, sched_setscheduler.2, select_tut.2, send.2, signalfd.2, splice.2, timerfd_create.2, write.2, flockfile.3, mkfifo.3, mq_notify.3, mq_open.3, pthread_tryjoin_np.3, scanf.3, random.4, ddp.7, epoll.7, fifo.7, ip.7, pipe.7, socket.7, spufs.7: Global fix: s/non-blocking/nonblocking/
The tendency in English, as prescribed in style guides like
Chicago MoS, is towards removing hyphens after prefixes
like "non-" etc.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-01-16 16:43:10 +00:00
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nonblocking read of the specified region into the page cache.
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2007-04-12 22:42:49 +00:00
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The amount of data read may be decreased by the kernel depending
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on virtual memory load.
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(A few megabytes will usually be fully satisfied,
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2006-09-26 12:41:08 +00:00
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and more is rarely useful.)
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2007-04-12 22:42:49 +00:00
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In kernels before 2.6.18, \fBPOSIX_FADV_NOREUSE\fP had the
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2006-09-26 12:41:08 +00:00
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same semantics as \fBPOSIX_FADV_WILLNEED\fP.
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This was probably a bug; since kernel 2.6.18, this flag is a no-op.
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2004-11-03 13:51:07 +00:00
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\fBPOSIX_FADV_DONTNEED\fP attempts to free cached pages associated with
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2007-04-12 22:42:49 +00:00
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the specified region.
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This is useful, for example, while streaming large
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files.
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A program may periodically request the kernel to free cached data
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that has already been used, so that more useful cached pages are not
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discarded instead.
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Pages that have not yet been written out will be unaffected, so if the
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application wishes to guarantee that pages will be released, it should
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2007-05-12 09:06:04 +00:00
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call
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.BR fsync (2)
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or
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.BR fdatasync (2)
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first.
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2010-10-09 04:50:38 +00:00
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.SS arm_fadvise()
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The ARM architecture
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needs 64-bit arguments to be aligned in a suitable pair of registers.
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On this architecture, the call signature of
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.BR posix_fadvise ()
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is flawed, since it forces a register to be wasted as padding between the
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.I fd
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and
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.I len
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arguments.
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Therefore, since Linux 2.6.14, ARM defines a different
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system call that orders the arguments suitably:
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.PP
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.in +4n
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.nf
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.BI "long arm_fadvise64_64(int " fd ", int " advice ,
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2011-09-08 14:13:09 +00:00
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.BI " loff_t " offset ", loff_t " len );
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2010-10-09 04:50:38 +00:00
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.fi
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.in
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.PP
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The behavior of this system call is otherwise exactly the same as
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2011-09-22 20:30:02 +00:00
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.BR posix_fadvise ().
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2010-10-09 04:50:38 +00:00
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No library support is provided for this system call in glibc.
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.\" No ARM support in glibc.
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2005-04-11 15:04:27 +00:00
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.SH BUGS
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2007-04-12 22:42:49 +00:00
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In kernels before 2.6.6, if
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2005-04-11 15:04:27 +00:00
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.I len
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was specified as 0, then this was interpreted literally as "zero bytes",
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rather than as meaning "all bytes through to the end of the file".
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2004-11-03 13:51:07 +00:00
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.SH "SEE ALSO"
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2006-05-29 05:47:49 +00:00
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.BR readahead (2),
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2010-06-15 01:27:10 +00:00
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.BR sync_file_range (2),
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2007-12-10 15:03:27 +00:00
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.BR posix_fallocate (3),
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getresuid.2, intro.2, mremap.2, open.2, poll.2, posix_fadvise.2, pread.2, remap_file_pages.2, setresuid.2, signal.2, splice.2, sync_file_range.2, tee.2, vmsplice.2, INFINITY.3, asprintf.3, assert_perror.3, basename.3, bsd_signal.3, canonicalize_file_name.3, clog10.3, crypt.3, dl_iterate_phdr.3, dlopen.3, dprintf.3, encrypt.3, exp10.3, fcloseall.3, fenv.3, ffs.3, fmemopen.3, fopencookie.3, ftw.3, getdate.3, getline.3, getloadavg.3, getopt.3, getsubopt.3, getutent.3, grantpt.3, hsearch.3, intro.3, lseek64.3, memmem.3, mempcpy.3, mq_receive.3, mq_send.3, posix_fallocate.3, pow10.3, program_invocation_name.3, ptsname.3, putgrent.3, readdir.3, sigset.3, sincos.3, stpcpy.3, stpncpy.3, strchr.3, strfry.3, strnlen.3, strptime.3, strsignal.3, strstr.3, strverscmp.3, swab.3, sysv_signal.3, tsearch.3, unlocked_stdio.3, unlockpt.3, wcpcpy.3, wcpncpy.3, wcsdup.3, wcwidth.3: SEE ALSO: Remove redundant reference to feature_test_macros(7)
Reported-by: Florian Lehmann <flo.lehmann@googlemail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-10-31 05:05:22 +00:00
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.BR posix_madvise (3)
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2008-04-28 18:27:36 +00:00
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.\" FIXME . Write a posix_fadvise(3) page.
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