From f551e44ff11d3e2ec8f37907bb88ec2433cc8b74 Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Wed, 20 Sep 2006 14:33:04 -0400 Subject: NFS: add comments clarifying the use of nfs_post_op_update() Comments-only change to clarify a detail of the NFS protocol and how it is implemented in Linux. Test plan: None. Signed-off-by: Chuck Lever Signed-off-by: Trond Myklebust --- fs/nfs/inode.c | 6 ++++++ fs/nfs/write.c | 8 +++++++- 2 files changed, 13 insertions(+), 1 deletion(-) diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c index a56add0bc5b7..e8c143d182c4 100644 --- a/fs/nfs/inode.c +++ b/fs/nfs/inode.c @@ -840,6 +840,12 @@ int nfs_refresh_inode(struct inode *inode, struct nfs_fattr *fattr) * * After an operation that has changed the inode metadata, mark the * attribute cache as being invalid, then try to update it. + * + * NB: if the server didn't return any post op attributes, this + * function will force the retrieval of attributes before the next + * NFS request. Thus it should be used only for operations that + * are expected to change one or more attributes, to avoid + * unnecessary NFS requests and trips through nfs_update_inode(). */ int nfs_post_op_update_inode(struct inode *inode, struct nfs_fattr *fattr) { diff --git a/fs/nfs/write.c b/fs/nfs/write.c index 38ba5c09af08..c12effb46fe5 100644 --- a/fs/nfs/write.c +++ b/fs/nfs/write.c @@ -1253,7 +1253,13 @@ int nfs_writeback_done(struct rpc_task *task, struct nfs_write_data *data) dprintk("NFS: %4d nfs_writeback_done (status %d)\n", task->tk_pid, task->tk_status); - /* Call the NFS version-specific code */ + /* + * ->write_done will attempt to use post-op attributes to detect + * conflicting writes by other clients. A strict interpretation + * of close-to-open would allow us to continue caching even if + * another writer had changed the file, but some applications + * depend on tighter cache coherency when writing. + */ status = NFS_PROTO(data->inode)->write_done(task, data); if (status != 0) return status; -- cgit v1.2.3