инициировать опережающее чтение файла в кеш страницы (initiate file readahead into page cache)
Имя (Name)
readahead - initiate file readahead into page cache
Синопсис (Synopsis)
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <fcntl.h>
ssize_t readahead(int fd, off64_t offset, size_t count);
Описание (Description)
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.
Возвращаемое значение (Return value)
On success, readahead() returns 0; on failure, -1 is returned,
with errno set to indicate the error.
Ошибки (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.
Версии (Versions)
The readahead() system call appeared in Linux 2.4.13; glibc
support has been provided since version 2.3.
Стандарты (Conforming to)
The readahead() system call is Linux-specific, and its use should
be avoided in portable applications.
Примечание (Note)
On some 32-bit architectures, the calling signature for this
system call differs, for the reasons described in syscall(2).
Ошибки (баги) (Bugs)
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[234] on large files using indirect
blocks instead of extents, giving the appearance that the call
blocks until the requested data has been read.
Смотри также (See also)
lseek(2), madvise(2), mmap(2), posix_fadvise(2), read(2)
