NFS: Add mount option 'softreval'

Add a mount option 'softreval' that allows attribute revalidation 'getattr'
calls to time out, and causes them to fall back to using the cached
attributes.
The use case for this option is for ensuring that we can still (slowly)
traverse paths and use cached information even when the server is down.
Once the server comes back up again, the getattr calls start succeeding,
and the caches will revalidate as usual.

The 'softreval' mount option is automatically enabled if you have
specified 'softerr'.  It can be turned off using the options
'nosoftreval', or 'hard'.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/fs_context.c

@@ -73,6 +73,7 @@ enum nfs_param {
 	Opt_sloppy,
 	Opt_soft,
 	Opt_softerr,
+	Opt_softreval,
 	Opt_source,
 	Opt_tcp,
 	Opt_timeo,
@@ -128,6 +129,7 @@ static const struct fs_parameter_spec nfs_param_specs[] = {
 	fsparam_flag  ("sloppy",	Opt_sloppy),
 	fsparam_flag  ("soft",		Opt_soft),
 	fsparam_flag  ("softerr",	Opt_softerr),
+	fsparam_flag  ("softreval",	Opt_softreval),
 	fsparam_string("source",	Opt_source),
 	fsparam_flag  ("tcp",		Opt_tcp),
 	fsparam_u32   ("timeo",		Opt_timeo),
@@ -460,11 +462,19 @@ static int nfs_fs_context_parse_param(struct fs_context *fc,
 		ctx->flags &= ~NFS_MOUNT_SOFTERR;
 		break;
 	case Opt_softerr:
-		ctx->flags |= NFS_MOUNT_SOFTERR;
+		ctx->flags |= NFS_MOUNT_SOFTERR | NFS_MOUNT_SOFTREVAL;
 		ctx->flags &= ~NFS_MOUNT_SOFT;
 		break;
 	case Opt_hard:
-		ctx->flags &= ~(NFS_MOUNT_SOFT|NFS_MOUNT_SOFTERR);
+		ctx->flags &= ~(NFS_MOUNT_SOFT |
+				NFS_MOUNT_SOFTERR |
+				NFS_MOUNT_SOFTREVAL);
+		break;
+	case Opt_softreval:
+		if (result.negated)
+			ctx->flags &= ~NFS_MOUNT_SOFTREVAL;
+		else
+			ctx->flags &= NFS_MOUNT_SOFTREVAL;
 		break;
 	case Opt_posix:
 		if (result.negated)

fs/nfs/inode.c

@@ -1156,7 +1156,13 @@ __nfs_revalidate_inode(struct nfs_server *server, struct inode *inode)
 		dfprintk(PAGECACHE, "nfs_revalidate_inode: (%s/%Lu) getattr failed, error=%d\n",
 			 inode->i_sb->s_id,
 			 (unsigned long long)NFS_FILEID(inode), status);
-		if (status == -ESTALE) {
+		switch (status) {
+		case -ETIMEDOUT:
+			/* A soft timeout occurred. Use cached information? */
+			if (server->flags & NFS_MOUNT_SOFTREVAL)
+				status = 0;
+			break;
+		case -ESTALE:
 			nfs_zap_caches(inode);
 			if (!S_ISDIR(inode->i_mode))
 				set_bit(NFS_INO_STALE, &NFS_I(inode)->flags);

fs/nfs/nfs3proc.c

@@ -110,10 +110,15 @@ nfs3_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle,
 		.rpc_resp	= fattr,
 	};
 	int	status;
+	unsigned short task_flags = 0;
+
+	/* Is this is an attribute revalidation, subject to softreval? */
+	if (inode && (server->flags & NFS_MOUNT_SOFTREVAL))
+		task_flags |= RPC_TASK_TIMEOUT;
 
 	dprintk("NFS call  getattr\n");
 	nfs_fattr_init(fattr);
-	status = rpc_call_sync(server->client, &msg, 0);
+	status = rpc_call_sync(server->client, &msg, task_flags);
 	dprintk("NFS reply getattr: %d\n", status);
 	return status;
 }

fs/nfs/nfs4proc.c

@@ -1097,11 +1097,12 @@ static int nfs4_call_sync_custom(struct rpc_task_setup *task_setup)
 	return ret;
 }
 
-static int nfs4_call_sync_sequence(struct rpc_clnt *clnt,
-				   struct nfs_server *server,
-				   struct rpc_message *msg,
-				   struct nfs4_sequence_args *args,
-				   struct nfs4_sequence_res *res)
+static int nfs4_do_call_sync(struct rpc_clnt *clnt,
+			     struct nfs_server *server,
+			     struct rpc_message *msg,
+			     struct nfs4_sequence_args *args,
+			     struct nfs4_sequence_res *res,
+			     unsigned short task_flags)
 {
 	struct nfs_client *clp = server->nfs_client;
 	struct nfs4_call_sync_data data = {
@@ -1113,12 +1114,23 @@ static int nfs4_call_sync_sequence(struct rpc_clnt *clnt,
 		.rpc_client = clnt,
 		.rpc_message = msg,
 		.callback_ops = clp->cl_mvops->call_sync_ops,
-		.callback_data = &data
+		.callback_data = &data,
+		.flags = task_flags,
 	};
 
 	return nfs4_call_sync_custom(&task_setup);
 }
 
+static int nfs4_call_sync_sequence(struct rpc_clnt *clnt,
+				   struct nfs_server *server,
+				   struct rpc_message *msg,
+				   struct nfs4_sequence_args *args,
+				   struct nfs4_sequence_res *res)
+{
+	return nfs4_do_call_sync(clnt, server, msg, args, res, 0);
+}
+
+
 int nfs4_call_sync(struct rpc_clnt *clnt,
 		   struct nfs_server *server,
 		   struct rpc_message *msg,
@@ -4064,11 +4076,18 @@ static int _nfs4_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle,
 		.rpc_argp = &args,
 		.rpc_resp = &res,
 	};
+	unsigned short task_flags = 0;
+
+	/* Is this is an attribute revalidation, subject to softreval? */
+	if (inode && (server->flags & NFS_MOUNT_SOFTREVAL))
+		task_flags |= RPC_TASK_TIMEOUT;
 
 	nfs4_bitmap_copy_adjust(bitmask, nfs4_bitmask(server, label), inode);
 
 	nfs_fattr_init(fattr);
-	return nfs4_call_sync(server->client, server, &msg, &args.seq_args, &res.seq_res, 0);
+	nfs4_init_sequence(&args.seq_args, &res.seq_res, 0, 0);
+	return nfs4_do_call_sync(server->client, server, &msg,
+			&args.seq_args, &res.seq_res, task_flags);
 }
 
 int nfs4_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle,

fs/nfs/proc.c

@@ -108,10 +108,15 @@ nfs_proc_getattr(struct nfs_server *server, struct nfs_fh *fhandle,
 		.rpc_resp	= fattr,
 	};
 	int	status;
+	unsigned short task_flags = 0;
+
+	/* Is this is an attribute revalidation, subject to softreval? */
+	if (inode && (server->flags & NFS_MOUNT_SOFTREVAL))
+		task_flags |= RPC_TASK_TIMEOUT;
 
 	dprintk("NFS call  getattr\n");
 	nfs_fattr_init(fattr);
-	status = rpc_call_sync(server->client, &msg, 0);
+	status = rpc_call_sync(server->client, &msg, task_flags);
 	dprintk("NFS reply getattr: %d\n", status);
 	return status;
 }

fs/nfs/super.c

@@ -375,6 +375,7 @@ static void nfs_show_mount_options(struct seq_file *m, struct nfs_server *nfss,
 	} nfs_info[] = {
 		{ NFS_MOUNT_SOFT, ",soft", "" },
 		{ NFS_MOUNT_SOFTERR, ",softerr", "" },
+		{ NFS_MOUNT_SOFTREVAL, ",softreval", "" },
 		{ NFS_MOUNT_POSIX, ",posix", "" },
 		{ NFS_MOUNT_NOCTO, ",nocto", "" },
 		{ NFS_MOUNT_NOAC, ",noac", "" },

include/linux/nfs_fs_sb.h

@@ -152,6 +152,7 @@ struct nfs_server {
 #define NFS_MOUNT_LOCAL_FLOCK		0x100000
 #define NFS_MOUNT_LOCAL_FCNTL		0x200000
 #define NFS_MOUNT_SOFTERR		0x400000
+#define NFS_MOUNT_SOFTREVAL		0x800000
 
 	unsigned int		caps;		/* server capabilities */
 	unsigned int		rsize;		/* read size */