K 10
svn:author
V 7
delphij
K 8
svn:date
V 27
2009-09-28T16:59:47.214637Z
K 7
svn:log
V 701
Add two new fcntls to enable/disable read-ahead:

 - F_READAHEAD: specify the amount for sequential access.  The amount is
   specified in bytes and is rounded up to nearest block size.
 - F_RDAHEAD: Darwin compatible version that use 128KB as the sequential
   access size.

A third argument of zero disables the read-ahead behavior.

Please note that the read-ahead amount is also constrainted by sysctl
variable, vfs.read_max, which may need to be raised in order to better
utilize this feature.

Thanks Igor Sysoev for proposing the feature and submitting the original
version, and kib@ for his valuable comments.

Submitted by:	Igor Sysoev <is rambler-co ru>
Reviewed by:	kib@
MFC after:	1 month

END