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readahead(2) [centos man page]

READAHEAD(2)						     Linux Programmer's Manual						      READAHEAD(2)

readahead - perform file readahead into page cache SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h> ssize_t readahead(int fd, off64_t offset, size_t count); DESCRIPTION
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. RETURN VALUE
On success, readahead() returns 0; on failure, -1 is returned, with errno set to indicate the cause of the error. ERRORS
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. VERSIONS
The readahead() system call appeared in Linux 2.4.13; glibc support has been provided since version 2.3. CONFORMING TO
The readahead() system call is Linux-specific, and its use should be avoided in portable applications. NOTES
On some 32-bit architectures, the calling signature for this system call differs, for the reasons described in syscall(2). SEE ALSO
lseek(2), madvise(2), mmap(2), posix_fadvise(2), read(2) COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at Linux 2013-04-01 READAHEAD(2)

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VFS_READAHEAD(8)					    System Administration tools 					  VFS_READAHEAD(8)

vfs_readahead - pre-load the kernel buffer cache SYNOPSIS
vfs objects = readahead DESCRIPTION
This VFS module is part of the samba(7) suite. This vfs_readahead VFS module detects read requests at multiples of a given offset (hex 0x80000 by default) and then tells the kernel via either the readahead system call (on Linux) or the posix_fadvise system call to pre-fetch this data into the buffer cache. This module is useful for Windows Vista clients reading data using the Windows Explorer program, which asynchronously does multiple file read requests at offset boundaries of 0x80000 bytes. The offset multiple used is given by the readahead:offset option, which defaults to 0x80000. The size of the disk read operations performed by vfs_readahead is determined by the readahead:length option. By default this is set to the same value as the readahead:offset option and if not set explicitly will use the current value of readahead:offset. This module is stackable. OPTIONS
readahead:offset = BYTES The offset multiple that causes readahead to be requested of the kernel buffer cache. readahead:length = BYTES The number of bytes requested to be read into the kernel buffer cache on each readahead call. The following suffixes may be applied to BYTES: o K - BYTES is a number of kilobytes o M - BYTES is a number of megabytes o G - BYTES is a number of gigabytes EXAMPLES
[hypothetical] vfs objects = readahead VERSION
This man page is correct for version 3.0.25 of the Samba suite. AUTHOR
The original Samba software and related utilities were created by Andrew Tridgell. Samba is now developed by the Samba Team as an Open Source project similar to the way the Linux kernel is developed. Samba 3.5 06/18/2010 VFS_READAHEAD(8)
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