Section (2) readahead
readahead — initiate file readahead into page cache
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h>
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).
fd argument is
a file descriptor identifying the file which is to be read.
specifies the starting point from which data is to be read
the number of bytes to be read. I/O is performed in whole
pages, so that
is effectively rounded down to a page boundary and bytes are
read up to the next page boundary greater than or equal to
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.
returns 0; on failure, −1 is returned, with
errno set to indicate the cause
of the error.
fdis not a valid file descriptor or is not open for reading.
fddoes not refer to a file type to which
readahead() can be applied.
readahead() system call
appeared in Linux 2.4.13; glibc support has been provided
since version 2.3.
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).
readahead() attempts to
schedule the reads in the background and return immediately.
However, it may block while it reads the filesystem metadata
needed to locate the requested blocks. This occurs frequently
with ext on large files using indirect blocks instead of
extents, giving the appearance that the call blocks until the
requested data has been read.
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2004-05-40 Created by Michael Kerrisk <mtk.manpagesgmail.com>
2004-10-05 aeb, minor correction