From a179ee09ab9ca2d9d1d09dc4752c53a13609f5e9 Mon Sep 17 00:00:00 2001 From: dillon Date: Thu, 24 May 2001 07:22:27 +0000 Subject: This patch implements O_DIRECT about 80% of the way. It takes a patchset Tor created a while ago, removes the raw I/O piece (that has cache coherency problems), and adds a buffer cache / VM freeing piece. Essentially this patch causes O_DIRECT I/O to not be left in the cache, but does not prevent it from going through the cache, hence the 80%. For the last 20% we need a method by which the I/O can be issued directly to buffer supplied by the user process and bypass the buffer cache entirely, but still maintain cache coherency. I also have the code working under -stable but the changes made to sys/file.h may not be MFCable, so an MFC is not on the table yet. Submitted by: tegge, dillon --- lib/libc/sys/open.2 | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'lib/libc/sys/open.2') diff --git a/lib/libc/sys/open.2 b/lib/libc/sys/open.2 index 769ac27..1a29a17 100644 --- a/lib/libc/sys/open.2 +++ b/lib/libc/sys/open.2 @@ -83,6 +83,7 @@ O_TRUNC truncate size to 0 O_EXCL error if create and file exists O_SHLOCK atomically obtain a shared lock O_EXLOCK atomically obtain an exclusive lock +O_DIRECT eliminate or reduce cache effects O_FSYNC synchronous writes O_NOFOLLOW do not follow symlinks .Ed @@ -150,6 +151,12 @@ If creating a file with the request for the lock will never fail (provided that the underlying filesystem supports locking). .Pp +.Dv O_DIRECT may be used to +minimize or eliminate the cache effects of reading and writing. The system +will attempt to avoid caching the data you read or write. If it cannot +avoid caching the data, it will minimize the impact the data has on the cache. +Use of this flag can drastically reduce performance if not used with care. +.Pp If successful, .Fn open returns a non-negative integer, termed a file descriptor. -- cgit v1.1