NFSv4: Make nfs4_state track O_RDWR, O_RDONLY and O_WRONLY separately

 A closer reading of RFC3530 reveals that OPEN_DOWNGRADE must always
 specify a access modes that have been the argument of a previous OPEN
 operation.
 IOW: doing OPEN(O_RDWR) and then OPEN_DOWNGRADE(O_WRONLY) is forbidden
 unless the user called OPEN(O_WRONLY)

 In order to fix that, we really need to track the three possible open
 states separately.
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/nfs4_fs.h

@@ -182,8 +182,9 @@ struct nfs4_state {
 
 	nfs4_stateid stateid;
 
-	unsigned int nreaders;
-	unsigned int nwriters;
+	unsigned int n_rdonly;
+	unsigned int n_wronly;
+	unsigned int n_rdwr;
 	int state;			/* State on the server (R,W, or RW) */
 	atomic_t count;
 };

fs/nfs/nfs4proc.c

@@ -297,6 +297,20 @@ static int nfs4_wait_for_completion_rpc_task(struct rpc_task *task)
 	return ret;
 }
 
+static inline void update_open_stateflags(struct nfs4_state *state, mode_t open_flags)
+{
+	switch (open_flags) {
+		case FMODE_WRITE:
+			state->n_wronly++;
+			break;
+		case FMODE_READ:
+			state->n_rdonly++;
+			break;
+		case FMODE_READ|FMODE_WRITE:
+			state->n_rdwr++;
+	}
+}
+
 static void update_open_stateid(struct nfs4_state *state, nfs4_stateid *stateid, int open_flags)
 {
 	struct inode *inode = state->inode;
@@ -306,10 +320,7 @@ static void update_open_stateid(struct nfs4_state *state, nfs4_stateid *stateid,
 	spin_lock(&state->owner->so_lock);
 	spin_lock(&inode->i_lock);
 	memcpy(&state->stateid, stateid, sizeof(state->stateid));
-	if ((open_flags & FMODE_WRITE))
-		state->nwriters++;
-	if (open_flags & FMODE_READ)
-		state->nreaders++;
+	update_open_stateflags(state, open_flags);
 	nfs4_state_set_mode_locked(state, state->state | open_flags);
 	spin_unlock(&inode->i_lock);
 	spin_unlock(&state->owner->so_lock);
@@ -822,10 +833,7 @@ static int _nfs4_open_delegated(struct inode *inode, int flags, struct rpc_cred
 	err = -ENOENT;
 	if ((state->state & open_flags) == open_flags) {
 		spin_lock(&inode->i_lock);
-		if (open_flags & FMODE_READ)
-			state->nreaders++;
-		if (open_flags & FMODE_WRITE)
-			state->nwriters++;
+		update_open_stateflags(state, open_flags);
 		spin_unlock(&inode->i_lock);
 		goto out_ok;
 	} else if (state->state != 0)
@@ -1082,10 +1090,12 @@ static void nfs4_close_prepare(struct rpc_task *task, void *data)
 	spin_lock(&state->owner->so_lock);
 	spin_lock(&calldata->inode->i_lock);
 	mode = old_mode = state->state;
-	if (state->nreaders == 0)
+	if (state->n_rdwr == 0) {
+		if (state->n_rdonly == 0)
 			mode &= ~FMODE_READ;
-	if (state->nwriters == 0)
+		if (state->n_wronly == 0)
 			mode &= ~FMODE_WRITE;
+	}
 	nfs4_state_set_mode_locked(state, mode);
 	spin_unlock(&calldata->inode->i_lock);
 	spin_unlock(&state->owner->so_lock);

fs/nfs/nfs4state.c

@@ -349,14 +349,9 @@ nfs4_alloc_open_state(void)
 {
 	struct nfs4_state *state;
 
-	state = kmalloc(sizeof(*state), GFP_KERNEL);
+	state = kzalloc(sizeof(*state), GFP_KERNEL);
 	if (!state)
 		return NULL;
-	state->state = 0;
-	state->nreaders = 0;
-	state->nwriters = 0;
-	state->flags = 0;
-	memset(state->stateid.data, 0, sizeof(state->stateid.data));
 	atomic_set(&state->count, 1);
 	INIT_LIST_HEAD(&state->lock_states);
 	spin_lock_init(&state->state_lock);
@@ -475,15 +470,23 @@ void nfs4_close_state(struct nfs4_state *state, mode_t mode)
 	/* Protect against nfs4_find_state() */
 	spin_lock(&owner->so_lock);
 	spin_lock(&inode->i_lock);
-	if (mode & FMODE_READ)
-		state->nreaders--;
-	if (mode & FMODE_WRITE)
-		state->nwriters--;
+	switch (mode & (FMODE_READ | FMODE_WRITE)) {
+		case FMODE_READ:
+			state->n_rdonly--;
+			break;
+		case FMODE_WRITE:
+			state->n_wronly--;
+			break;
+		case FMODE_READ|FMODE_WRITE:
+			state->n_rdwr--;
+	}
 	oldstate = newstate = state->state;
-	if (state->nreaders == 0)
+	if (state->n_rdwr == 0) {
+		if (state->n_rdonly == 0)
 			newstate &= ~FMODE_READ;
-	if (state->nwriters == 0)
+		if (state->n_wronly == 0)
 			newstate &= ~FMODE_WRITE;
+	}
 	if (test_bit(NFS_DELEGATED_STATE, &state->flags)) {
 		nfs4_state_set_mode_locked(state, newstate);
 		oldstate = newstate;