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       readahead - perform file readahead into page cache


       #define _GNU_SOURCE             /* See feature_test_macros(7) */
       #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 applied.


       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


       On some 32-bit architectures, the calling signature for this system call differs, for  the
       reasons described in syscall(2).


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


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