1READAHEAD(2) Linux Programmer's Manual READAHEAD(2)
2
6 readahead - perform file readahead into page cache
7
9 #define _GNU_SOURCE
10 #include <fcntl.h>
11 ssize_t readahead(int fd, off64_t offset, size_t count);
13
15 readahead() populates the page cache with data from a file so that sub‐
16 sequent reads from that file will not block on disk I/O. The fd argu‐
17 ment is a file descriptor identifying the file which is to be read.
18 The offset argument specifies the starting point from which data is to
19 be read and count specifies the number of bytes to be read. I/O is
20 performed in whole pages, so that offset is effectively rounded down to
21 a page boundary and bytes are read up to the next page boundary greater
22 than or equal to (offset+count). readahead() does not read beyond the
23 end of the file. readahead() blocks until the specified data has been
24 read. The current file offset of the open file referred to by fd is
25 left unchanged.
26
28 On success, readahead() returns 0; on failure, -1 is returned, with
29 errno set to indicate the cause of the error.
30
32 EBADF fd is not a valid file descriptor or is not open for reading.
33 EINVAL fd does not refer to a file type to which readahead() can be
35 applied.
36
38 The readahead() system call appeared in Linux 2.4.13; glibc support has
39 been provided since version 2.3.
40
42 The readahead() system call is Linux-specific, and its use should be
43 avoided in portable applications.
44
46 lseek(2), madvise(2), mmap(2), posix_fadvise(2), read(2)
47
49 This page is part of release 3.25 of the Linux man-pages project. A
50 description of the project, and information about reporting bugs, can
51 be found at http://www.kernel.org/doc/man-pages/.
52Linux 2007-07-26 READAHEAD(2)