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       readahead - perform file readahead into page cache


       #define _GNU_SOURCE
       #include <fcntl.h>

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


       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 offset of the open file referred to  by  fd  is
       left unchanged.


       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)


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