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| author | Alejandro Colomar <alx@kernel.org> | 2024-04-26 15:06:49 +0200 |
|---|---|---|
| committer | Alejandro Colomar <alx@kernel.org> | 2024-05-02 01:24:19 +0200 |
| commit | dcde2f70372b49ec43efc5db864c9ff585d0a2dd (patch) | |
| tree | 78b9b7425130e4a5858e4c01a524d802423879ed /man/man2/readahead.2 | |
| parent | 12aca537ce78a41bbcdaf485209691e10f8002d7 (diff) | |
| download | man-pages-dcde2f70372b49ec43efc5db864c9ff585d0a2dd.tar.gz | |
man/, share/mk/: Move man*/ to man/
This is a scripted change:
$ mkdir man/;
$ mv man* man/;
$ ln -st . man/man*;
$ find share/mk/ -type f \
| xargs grep -l '^MANDIR *:=' \
| xargs sed -i '/^MANDIR *:=/s,$,/man,';
$ find share/mk/dist/ -type f \
| xargs grep -l man \
| xargs sed -i 's,man%,man/%,g';
Link: <https://lore.kernel.org/linux-man/YxcV4h+Xn7cd6+q2@pevik/T/>
Cc: Petr Vorel <pvorel@suse.cz>
Cc: Jakub Wilk <jwilk@jwilk.net>
Cc: Stefan Puiu <stefan.puiu@gmail.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
Diffstat (limited to 'man/man2/readahead.2')
| -rw-r--r-- | man/man2/readahead.2 | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/man/man2/readahead.2 b/man/man2/readahead.2 new file mode 100644 index 0000000000..e857fde664 --- /dev/null +++ b/man/man2/readahead.2 @@ -0,0 +1,99 @@ +.\" This manpage is Copyright (C) 2004, Michael Kerrisk +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" 2004-05-40 Created by Michael Kerrisk <mtk.manpages@gmail.com> +.\" 2004-10-05 aeb, minor correction +.\" +.TH readahead 2 (date) "Linux man-pages (unreleased)" +.SH NAME +readahead \- initiate file readahead into page cache +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" +.B #define _FILE_OFFSET_BITS 64 +.B #include <fcntl.h> +.P +.BI "ssize_t readahead(int " fd ", off_t " offset ", size_t " count ); +.fi +.SH DESCRIPTION +.BR readahead () +initiates readahead on a file so that subsequent reads from that file will +be satisfied from the cache, and not block on disk I/O +(assuming the readahead was initiated early enough and that other activity +on the system did not in the meantime flush pages from the cache). +.P +The +.I fd +argument is a file descriptor identifying the file which is +to be read. +The +.I offset +argument specifies the starting point from which data is to be read +and +.I count +specifies the number of bytes to be read. +I/O is performed in whole pages, so that +.I offset +is effectively rounded down to a page boundary +and bytes are read up to the next page boundary greater than or +equal to +.IR "(offset+count)" . +.BR readahead () +does not read beyond the end of the file. +The file offset of the open file description referred to by the file descriptor +.I fd +is left unchanged. +.SH RETURN VALUE +On success, +.BR readahead () +returns 0; on failure, \-1 is returned, with +.I errno +set to indicate the error. +.SH ERRORS +.TP +.B EBADF +.I fd +is not a valid file descriptor or is not open for reading. +.TP +.B EINVAL +.I fd +does not refer to a file type to which +.BR readahead () +can be applied. +.SH VERSIONS +On some 32-bit architectures, +the calling signature for this system call differs, +for the reasons described in +.BR syscall (2). +.SH STANDARDS +Linux. +.SH HISTORY +Linux 2.4.13, +glibc 2.3. +.SH NOTES +.B _FILE_OFFSET_BITS +should be defined to be 64 in code that uses a pointer to +.BR readahead , +if the code is intended to be portable +to traditional 32-bit x86 and ARM platforms where +.BR off_t 's +width defaults to 32 bits. +.SH BUGS +.BR readahead () +attempts to schedule the reads in the background and return immediately. +However, it may block while it reads the filesystem metadata needed +to locate the requested blocks. +This occurs frequently with ext[234] on large files +using indirect blocks instead of extents, +giving the appearance that the call blocks until the requested data has +been read. +.SH SEE ALSO +.BR lseek (2), +.BR madvise (2), +.BR mmap (2), +.BR posix_fadvise (2), +.BR read (2) |