projects / thirdparty / man-pages.git / blame
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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| 15 | .\" manual page may be incorrect or out-of-date.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> |
| fea681da MK |
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 | |
| 35 | .B 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 | .B readahead() | |
| 55 | does not read beyond the end of the file. | |
| 56 | .B 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 | .B 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 | .B readahead | |
| 77 | can be applied. | |
| 78 | .SH "CONFORMING TO" | |
| 79 | The | |
| 80 | .B readahead() | |
| 81 | system call is Linux specific, and its use should be avoided | |
| 82 | in portable applications. | |
| 83 | .SH NOTES | |
| 84 | The | |
| 85 | .B 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 read (2) |