From a707c9a8380f1f4da0ee907a7ff9eaa976df29b1 Mon Sep 17 00:00:00 2001 From: Mike Snitzer Date: Fri, 15 Nov 2024 20:40:53 -0500 Subject: nfs/localio: add direct IO enablement with sync and async IO support [ Upstream commit 3feec68563dda59517f83d19123aa287a1dfd068 ] This commit simply adds the required O_DIRECT plumbing. It doesn't address the fact that NFS doesn't ensure all writes are page aligned (nor device logical block size aligned as required by O_DIRECT). Because NFS will read-modify-write for IO that isn't aligned, LOCALIO will not use O_DIRECT semantics by default if/when an application requests the use of O_DIRECT. Allow the use of O_DIRECT semantics by: 1: Adding a flag to the nfs_pgio_header struct to allow the NFS O_DIRECT layer to signal that O_DIRECT was used by the application 2: Adding a 'localio_O_DIRECT_semantics' NFS module parameter that when enabled will cause LOCALIO to use O_DIRECT semantics (this may cause IO to fail if applications do not properly align their IO). This commit is derived from code developed by Weston Andros Adamson. Signed-off-by: Mike Snitzer Reviewed-by: Jeff Layton Signed-off-by: Anna Schumaker Stable-dep-of: 992203a1fba5 ("nfs/localio: restore creds before releasing pageio data") Signed-off-by: Sasha Levin --- Documentation/filesystems/nfs/localio.rst | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'Documentation') diff --git a/Documentation/filesystems/nfs/localio.rst b/Documentation/filesystems/nfs/localio.rst index bd1967e2eab3..20fc901a08f4 100644 --- a/Documentation/filesystems/nfs/localio.rst +++ b/Documentation/filesystems/nfs/localio.rst @@ -306,6 +306,19 @@ is issuing IO to the underlying local filesystem that it is sharing with the NFS server. See: fs/nfs/localio.c:nfs_local_doio() and fs/nfs/localio.c:nfs_local_commit(). +With normal NFS that makes use of RPC to issue IO to the server, if an +application uses O_DIRECT the NFS client will bypass the pagecache but +the NFS server will not. Because the NFS server's use of buffered IO +affords applications to be less precise with their alignment when +issuing IO to the NFS client. LOCALIO can be configured to use O_DIRECT +semantics by setting the 'localio_O_DIRECT_semantics' nfs module +parameter to Y, e.g.: + + echo Y > /sys/module/nfs/parameters/localio_O_DIRECT_semantics + +Once enabled, it will cause LOCALIO to use O_DIRECT semantics (this may +cause IO to fail if applications do not properly align their IO). + Security ======== -- cgit v1.2.3