man2/readahead.2

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  25 .\" 2004-05-40 Created by Michael Kerrisk <mtk.manpages@gmail.com>
  26 .\" 2004-10-05 aeb, minor correction
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  28 .TH READAHEAD 2 2010-09-10 "Linux" "Linux Programmer's Manual"
  29 .SH NAME
  30 readahead \- perform file readahead into page cache
  31 .SH SYNOPSIS
  32 .nf
  33 .BR "#define _GNU_SOURCE" "             /* See feature_test_macros(7) */"
  34 .B #include <fcntl.h>
  35 .sp
  36 .BI "ssize_t readahead(int " fd ", off64_t " offset ", size_t " count );
  37 .fi
  38 .SH DESCRIPTION
  39 .BR readahead ()
  40 populates the page cache with data from a file so that subsequent
  41 reads from that file will not block on disk I/O.
  42 The
  43 .I fd
  44 argument is a file descriptor identifying the file which is
  45 to be read.
  46 The
  47 .I offset
  48 argument specifies the starting point from which data is to be read
  49 and
  50 .I count
  51 specifies the number of bytes to be read.
  52 I/O is performed in whole pages, so that
  53 .I offset
  54 is effectively rounded down to a page boundary
  55 and bytes are read up to the next page boundary greater than or
  56 equal to
  57 .IR "(offset+count)" .
  58 .BR readahead ()
  59 does not read beyond the end of the file.
  60 .BR readahead ()
  61 blocks until the specified data has been read.
  62 The current file offset of the open file referred to by
  63 .I fd
  64 is left unchanged.
  65 .SH "RETURN VALUE"
  66 On success,
  67 .BR readahead ()
  68 returns 0; on failure, \-1 is returned, with
  69 .I errno
  70 set to indicate the cause of the error.
  71 .SH ERRORS
  72 .TP
  73 .B EBADF
  74 .I fd
  75 is not a valid file descriptor or is not open for reading.
  76 .TP
  77 .B EINVAL
  78 .I fd
  79 does not refer to a file type to which
  80 .BR readahead ()
  81 can be applied.
  82 .SH VERSIONS
  83 The
  84 .BR readahead ()
  85 system call appeared in Linux 2.4.13;
  86 glibc support has been provided since version 2.3.
  87 .SH "CONFORMING TO"
  88 The
  89 .BR readahead ()
  90 system call is Linux-specific, and its use should be avoided
  91 in portable applications.
  92 .SH "SEE ALSO"
  93 .BR lseek (2),
  94 .BR madvise (2),
  95 .BR mmap (2),
  96 .BR posix_fadvise (2),
  97 .BR read (2)