From 399644e47874bff147afb19c89228901ac39340e Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 15 Apr 2024 21:40:15 +0200 Subject: Adding upstream version 6.05.01. Signed-off-by: Daniel Baumann --- man2/readahead.2 | 99 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 99 insertions(+) create mode 100644 man2/readahead.2 (limited to 'man2/readahead.2') diff --git a/man2/readahead.2 b/man2/readahead.2 new file mode 100644 index 0000000..b97f085 --- /dev/null +++ b/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 +.\" 2004-10-05 aeb, minor correction +.\" +.TH readahead 2 2023-07-15 "Linux man-pages 6.05.01" +.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 +.PP +.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). +.PP +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) -- cgit v1.2.3