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1 | .\" Hey Emacs! This file is -*- nroff -*- source. |
2 | .\" | |
3 | .\" This manpage is Copyright (C) 2004, Michael Kerrisk | |
4 | .\" | |
5 | .\" Permission is granted to make and distribute verbatim copies of this | |
6 | .\" manual provided the copyright notice and this permission notice are | |
7 | .\" preserved on all copies. | |
8 | .\" | |
9 | .\" Permission is granted to copy and distribute modified versions of this | |
10 | .\" manual under the conditions for verbatim copying, provided that the | |
11 | .\" entire resulting derived work is distributed under the terms of a | |
12 | .\" permission notice identical to this one. | |
13 | .\" | |
14 | .\" Since the Linux kernel and libraries are constantly changing, this | |
15 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
16 | .\" responsibility for errors or omissions, or for damages resulting from | |
17 | .\" the use of the information contained herein. | |
18 | .\" | |
19 | .\" Formatted or processed versions of this manual, if unaccompanied by | |
20 | .\" the source, must acknowledge the copyright and authors of this work. | |
21 | .\" | |
305a0578 | 22 | .\" 2004-05-40 Created by Michael Kerrisk <mtk-manpages@gmx.net> |
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23 | .\" 2004-10-05 aeb, minor correction |
24 | .\" | |
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 | |
63aa9df0 | 35 | .BR readahead () |
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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)" . | |
63aa9df0 | 54 | .BR readahead () |
fea681da | 55 | does not read beyond the end of the file. |
63aa9df0 | 56 | .BR readahead () |
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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, | |
63aa9df0 | 63 | .BR readahead () |
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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 | |
e511ffb6 | 76 | .BR readahead () |
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77 | can be applied. |
78 | .SH "CONFORMING TO" | |
79 | The | |
63aa9df0 | 80 | .BR readahead () |
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81 | system call is Linux specific, and its use should be avoided |
82 | in portable applications. | |
83 | .SH NOTES | |
84 | The | |
63aa9df0 | 85 | .BR readahead () |
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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 read (2) |