]>
Commit | Line | Data |
---|---|---|
fea681da MK |
1 | .\" This manpage is Copyright (C) 2004, Michael Kerrisk |
2 | .\" | |
93015253 | 3 | .\" %%%LICENSE_START(VERBATIM) |
fea681da MK |
4 | .\" Permission is granted to make and distribute verbatim copies of this |
5 | .\" manual provided the copyright notice and this permission notice are | |
6 | .\" preserved on all copies. | |
7 | .\" | |
8 | .\" Permission is granted to copy and distribute modified versions of this | |
9 | .\" manual under the conditions for verbatim copying, provided that the | |
10 | .\" entire resulting derived work is distributed under the terms of a | |
11 | .\" permission notice identical to this one. | |
c13182ef | 12 | .\" |
fea681da MK |
13 | .\" Since the Linux kernel and libraries are constantly changing, this |
14 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
15 | .\" responsibility for errors or omissions, or for damages resulting from | |
10d76543 MK |
16 | .\" the use of the information contained herein. The author(s) may not |
17 | .\" have taken the same level of care in the production of this manual, | |
18 | .\" which is licensed free of charge, as they might when working | |
19 | .\" professionally. | |
c13182ef | 20 | .\" |
fea681da MK |
21 | .\" Formatted or processed versions of this manual, if unaccompanied by |
22 | .\" the source, must acknowledge the copyright and authors of this work. | |
4b72fb64 | 23 | .\" %%%LICENSE_END |
fea681da | 24 | .\" |
c11b1abf | 25 | .\" 2004-05-40 Created by Michael Kerrisk <mtk.manpages@gmail.com> |
fea681da MK |
26 | .\" 2004-10-05 aeb, minor correction |
27 | .\" | |
86b91fdf | 28 | .TH READAHEAD 2 2010-09-10 "Linux" "Linux Programmer's Manual" |
fea681da MK |
29 | .SH NAME |
30 | readahead \- perform file readahead into page cache | |
31 | .SH SYNOPSIS | |
32 | .nf | |
86b91fdf | 33 | .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" |
fea681da MK |
34 | .B #include <fcntl.h> |
35 | .sp | |
37cd82ad | 36 | .BI "ssize_t readahead(int " fd ", off64_t " offset ", size_t " count ); |
fea681da MK |
37 | .fi |
38 | .SH DESCRIPTION | |
63aa9df0 | 39 | .BR readahead () |
fea681da MK |
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. | |
c13182ef | 52 | I/O is performed in whole pages, so that |
fea681da MK |
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)" . | |
63aa9df0 | 58 | .BR readahead () |
fea681da | 59 | does not read beyond the end of the file. |
63aa9df0 | 60 | .BR readahead () |
fea681da MK |
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. | |
47297adb | 65 | .SH RETURN VALUE |
c13182ef | 66 | On success, |
63aa9df0 | 67 | .BR readahead () |
fea681da MK |
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 | |
e511ffb6 | 80 | .BR readahead () |
fea681da | 81 | can be applied. |
0f940346 MK |
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. | |
47297adb | 87 | .SH CONFORMING TO |
c13182ef | 88 | The |
63aa9df0 | 89 | .BR readahead () |
8382f16d | 90 | system call is Linux-specific, and its use should be avoided |
fea681da | 91 | in portable applications. |
47297adb | 92 | .SH SEE ALSO |
fea681da MK |
93 | .BR lseek (2), |
94 | .BR madvise (2), | |
95 | .BR mmap (2), | |
cedfddcd | 96 | .BR posix_fadvise (2), |
fea681da | 97 | .BR read (2) |