READAHEAD(2)                                        Linux Programmer's Manual                                       READAHEAD(2)



NAME
       readahead - perform file readahead into page cache

SYNOPSIS
       #define _GNU_SOURCE
       #include <fcntl.h>

       ssize_t readahead(int fd, off64_t offset, size_t count);

DESCRIPTION
       readahead() populates the page cache with data from a file so that subsequent reads from that file will not block on disk
       I/O.  The fd argument 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  bound-
       ary  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 left unchanged.

RETURN VALUE
       On success, readahead() returns 0; on failure, -1 is returned, with errno set to indicate the cause of the error.

ERRORS
       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 applied.

VERSIONS
       The readahead() system call appeared in Linux 2.4.13; glibc support has been provided since version 2.3.

CONFORMING TO
       The readahead() system call is Linux-specific, and its use should be avoided in portable applications.

SEE ALSO
       lseek(2), madvise(2), mmap(2), posix_fadvise(2), read(2)

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2007-07-26                                               READAHEAD(2)