man2/readahead.2

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  22 .\" 2004-05-40 Created by Michael Kerrisk <mtk-manpages@gmx.net>
  23 .\" 2004-10-05 aeb, minor correction
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  25 .TH READAHEAD 2 2004-10-05 "Linux 2.6.5" "Linux Programmer's Manual"
  26 .SH NAME
  27 readahead \- perform file readahead into page cache
  28 .SH SYNOPSIS
  29 .nf
  30 .B #include <fcntl.h>
  31 .sp
  32 .BI "ssize_t readahead(int " fd ", off64_t *" offset ", size_t " count );
  33 .fi
  34 .SH DESCRIPTION
  35 .BR readahead ()
  36 populates the page cache with data from a file so that subsequent
  37 reads from that file will not block on disk I/O.
  38 The
  39 .I fd
  40 argument is a file descriptor identifying the file which is
  41 to be read.
  42 The
  43 .I offset
  44 argument specifies the starting point from which data is to be read
  45 and
  46 .I count
  47 specifies the number of bytes to be read.
  48 I/O is performed in whole pages, so that
  49 .I offset
  50 is effectively rounded down to a page boundary
  51 and bytes are read up to the next page boundary greater than or
  52 equal to
  53 .IR "(offset+count)" .
  54 .BR readahead ()
  55 does not read beyond the end of the file.
  56 .BR readahead ()
  57 blocks until the specified data has been read.
  58 The current file offset of the open file referred to by
  59 .I fd
  60 is left unchanged.
  61 .SH "RETURN VALUE"
  62 On success,
  63 .BR readahead ()
  64 returns 0; on failure, \-1 is returned, with
  65 .I errno
  66 set to indicate the cause of the error.
  67 .SH ERRORS
  68 .TP
  69 .B EBADF
  70 .I fd
  71 is not a valid file descriptor or is not open for reading.
  72 .TP
  73 .B EINVAL
  74 .I fd
  75 does not refer to a file type to which
  76 .BR readahead ()
  77 can be applied.
  78 .SH "CONFORMING TO"
  79 The
  80 .BR readahead ()
  81 system call is Linux specific, and its use should be avoided
  82 in portable applications.
  83 .SH NOTES
  84 The
  85 .BR readahead ()
  86 system call appeared in Linux 2.4.13.
  87 .SH "SEE ALSO"
  88 .BR fadvise (2),
  89 .BR lseek (2),
  90 .BR madvise (2),
  91 .BR mmap (2),
  92 .BR posix_fadvise (2),
  93 .BR read (2)