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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 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  off-
       set 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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2007-07-26                      READAHEAD(2)