#define _GNU_SOURCE /* See feature_test_macros(7) */
ssize_t readahead(int fd, off64_t offset, size_t count);
readahead() populates the page cache with data from a file so that sub-
sequent reads from that file will not block on disk I/O. The fd argu-
ment is a file descriptor identifying the file which is to be read.
The offset argument specifies the starting point from which data is to
be read and count specifies the number of bytes to be read. I/O is
performed in whole pages, so that offset is effectively rounded down to
a page boundary and bytes are read up to the next page boundary greater
than or equal to (offset+count). readahead() does not read beyond the
end of the file. readahead() blocks until the specified data has been
read. The current file offset of the open file referred to by fd is
On success, readahead() returns 0; on failure, -1 is returned, with
errno set to indicate the cause of the error.
EBADF fd is not a valid file descriptor or is not open for reading.
EINVAL fd does not refer to a file type to which readahead() can be
The readahead() system call appeared in Linux 2.4.13; glibc support has
been provided since version 2.3.
The readahead() system call is Linux-specific, and its use should be
avoided in portable applications.
lseek(2), madvise(2), mmap(2), posix_fadvise(2), read(2)
This page is part of release 3.35 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://man7.org/linux/man-pages/.
Linux 2010-09-10 READAHEAD(2)
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