readahead - initiate file readahead into page cache
#define _GNU_SOURCE /* See feature_test_macros(7) */
#define _FILE_OFFSET_BITS 64
#include <fcntl.h>
ssize_t readahead(int fd, off_t offset, size_t count);
readahead() initiates readahead on a file so that subsequent reads from that file will be satisfied from the cache, and not block on disk I/O (assuming the readahead was initiated early enough and that other activity on the system did not in the meantime flush pages from the cache).
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. The file offset of the open file description
referred to by the file descriptor fd
is left unchanged.
On success, readahead() returns 0; on failure, -1 is
returned, with errno
set to indicate the error.
lseek(2), madvise(2), mmap(2), posix_fadvise(2), read(2)