From: Chuck Lever the final patch in this series adds an option in fs/Kconfig to allow NFS O_DIRECT to be enabled or disabled. fs/Kconfig | 24 ++++++++++++++++++++++++ 1 files changed, 24 insertions(+) diff -puN fs/Kconfig~nfs-O_DIRECT-config-option fs/Kconfig --- 25/fs/Kconfig~nfs-O_DIRECT-config-option 2003-06-17 16:00:30.000000000 -0700 +++ 25-akpm/fs/Kconfig 2003-06-17 16:00:30.000000000 -0700 @@ -1323,6 +1323,30 @@ config NFS_V4 If unsure, say N. +config NFS_DIRECTIO + bool "Allow direct I/O on NFS files (EXPERIMENTAL)" + depends on NFS_FS && EXPERIMENTAL + help + This option enables applications to perform uncached I/O on files + in NFS file systems using the O_DIRECT open() flag. When O_DIRECT + is set for a file, its data is not cached in the system's page + cache. Data is moved to and from user-level application buffers + directly. Unlike local disk-based file systems, NFS O_DIRECT has + no alignment restrictions. + + Unless your program is designed to use O_DIRECT properly, you are + much better off allowing the NFS client to manage data caching for + you. Misusing O_DIRECT can cause poor server performance or network + storms. This kernel build option defaults OFF to avoid exposing + system administrators unwittingly to a potentially hazardous + feature. + + For more details on NFS O_DIRECT, see fs/nfs/direct.c. + + If unsure, say N. This reduces the size of the NFS client, and + causes open() to return EINVAL if a file residing in NFS is + opened with the O_DIRECT flag. + config NFSD tristate "NFS server support" depends on INET _