[PATCH] FUSE - mount options

This patch adds miscellaneous mount options to the FUSE filesystem.

The following mount options are added:

 o default_permissions:  check permissions with generic_permission()
 o allow_other:          allow other users to access files
 o allow_root:           allow root to access files
 o kernel_cache:         don't invalidate page cache on open

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/fuse/dev.c

@@ -26,7 +26,7 @@ static inline struct fuse_conn *fuse_get_conn(struct file *file)
 	struct fuse_conn *fc;
 	spin_lock(&fuse_lock);
 	fc = file->private_data;
-	if (fc && !fc->sb)
+	if (fc && !fc->mounted)
 		fc = NULL;
 	spin_unlock(&fuse_lock);
 	return fc;
@@ -148,6 +148,17 @@ void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req)
 		fuse_putback_request(fc, req);
 }
 
+void fuse_release_background(struct fuse_req *req)
+{
+	iput(req->inode);
+	iput(req->inode2);
+	if (req->file)
+		fput(req->file);
+	spin_lock(&fuse_lock);
+	list_del(&req->bg_entry);
+	spin_unlock(&fuse_lock);
+}
+
 /*
  * This function is called when a request is finished.  Either a reply
  * has arrived or it was interrupted (and not yet sent) or some error
@@ -166,12 +177,10 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
 	putback = atomic_dec_and_test(&req->count);
 	spin_unlock(&fuse_lock);
 	if (req->background) {
-		if (req->inode)
-			iput(req->inode);
-		if (req->inode2)
-			iput(req->inode2);
-		if (req->file)
-			fput(req->file);
+		down_read(&fc->sbput_sem);
+		if (fc->mounted)
+			fuse_release_background(req);
+		up_read(&fc->sbput_sem);
 	}
 	wake_up(&req->waitq);
 	if (req->in.h.opcode == FUSE_INIT) {
@@ -191,11 +200,39 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
 		fuse_putback_request(fc, req);
 }
 
-static void background_request(struct fuse_req *req)
+/*
+ * Unfortunately request interruption not just solves the deadlock
+ * problem, it causes problems too.  These stem from the fact, that an
+ * interrupted request is continued to be processed in userspace,
+ * while all the locks and object references (inode and file) held
+ * during the operation are released.
+ *
+ * To release the locks is exactly why there's a need to interrupt the
+ * request, so there's not a lot that can be done about this, except
+ * introduce additional locking in userspace.
+ *
+ * More important is to keep inode and file references until userspace
+ * has replied, otherwise FORGET and RELEASE could be sent while the
+ * inode/file is still used by the filesystem.
+ *
+ * For this reason the concept of "background" request is introduced.
+ * An interrupted request is backgrounded if it has been already sent
+ * to userspace.  Backgrounding involves getting an extra reference to
+ * inode(s) or file used in the request, and adding the request to
+ * fc->background list.  When a reply is received for a background
+ * request, the object references are released, and the request is
+ * removed from the list.  If the filesystem is unmounted while there
+ * are still background requests, the list is walked and references
+ * are released as if a reply was received.
+ *
+ * There's one more use for a background request.  The RELEASE message is
+ * always sent as background, since it doesn't return an error or
+ * data.
+ */
+static void background_request(struct fuse_conn *fc, struct fuse_req *req)
 {
-	/* Need to get hold of the inode(s) and/or file used in the
-	   request, so FORGET and RELEASE are not sent too early */
 	req->background = 1;
+	list_add(&req->bg_entry, &fc->background);
 	if (req->inode)
 		req->inode = igrab(req->inode);
 	if (req->inode2)
@@ -215,7 +252,8 @@ static int request_wait_answer_nonint(struct fuse_req *req)
 }
 
 /* Called with fuse_lock held.  Releases, and then reacquires it. */
-static void request_wait_answer(struct fuse_req *req, int interruptible)
+static void request_wait_answer(struct fuse_conn *fc, struct fuse_req *req,
+				int interruptible)
 {
 	int intr;
 
@@ -255,7 +293,7 @@ static void request_wait_answer(struct fuse_req *req, int interruptible)
 		list_del(&req->list);
 		__fuse_put_request(req);
 	} else if (!req->finished && req->sent)
-		background_request(req);
+		background_request(fc, req);
 }
 
 static unsigned len_args(unsigned numargs, struct fuse_arg *args)
@@ -297,7 +335,7 @@ static void request_send_wait(struct fuse_conn *fc, struct fuse_req *req,
 {
 	req->isreply = 1;
 	spin_lock(&fuse_lock);
-	if (!fc->file)
+	if (!fc->connected)
 		req->out.h.error = -ENOTCONN;
 	else if (fc->conn_error)
 		req->out.h.error = -ECONNREFUSED;
@@ -307,7 +345,7 @@ static void request_send_wait(struct fuse_conn *fc, struct fuse_req *req,
 		   after request_end() */
 		__fuse_get_request(req);
 
-		request_wait_answer(req, interruptible);
+		request_wait_answer(fc, req, interruptible);
 	}
 	spin_unlock(&fuse_lock);
 }
@@ -330,7 +368,7 @@ void request_send_nonint(struct fuse_conn *fc, struct fuse_req *req)
 static void request_send_nowait(struct fuse_conn *fc, struct fuse_req *req)
 {
 	spin_lock(&fuse_lock);
-	if (fc->file) {
+	if (fc->connected) {
 		queue_request(fc, req);
 		spin_unlock(&fuse_lock);
 	} else {
@@ -348,7 +386,9 @@ void request_send_noreply(struct fuse_conn *fc, struct fuse_req *req)
 void request_send_background(struct fuse_conn *fc, struct fuse_req *req)
 {
 	req->isreply = 1;
-	background_request(req);
+	spin_lock(&fuse_lock);
+	background_request(fc, req);
+	spin_unlock(&fuse_lock);
 	request_send_nowait(fc, req);
 }
 
@@ -583,7 +623,7 @@ static void request_wait(struct fuse_conn *fc)
 	DECLARE_WAITQUEUE(wait, current);
 
 	add_wait_queue_exclusive(&fc->waitq, &wait);
-	while (fc->sb && list_empty(&fc->pending)) {
+	while (fc->mounted && list_empty(&fc->pending)) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		if (signal_pending(current))
 			break;
@@ -622,7 +662,7 @@ static ssize_t fuse_dev_readv(struct file *file, const struct iovec *iov,
 		goto err_unlock;
 	request_wait(fc);
 	err = -ENODEV;
-	if (!fc->sb)
+	if (!fc->mounted)
 		goto err_unlock;
 	err = -ERESTARTSYS;
 	if (list_empty(&fc->pending))
@@ -839,7 +879,7 @@ static int fuse_dev_release(struct inode *inode, struct file *file)
 	spin_lock(&fuse_lock);
 	fc = file->private_data;
 	if (fc) {
-		fc->file = NULL;
+		fc->connected = 0;
 		end_requests(fc, &fc->pending);
 		end_requests(fc, &fc->processing);
 		fuse_release_conn(fc);

fs/fuse/dir.c

@@ -418,7 +418,8 @@ static int fuse_revalidate(struct dentry *entry)
 	struct fuse_conn *fc = get_fuse_conn(inode);
 
 	if (get_node_id(inode) == FUSE_ROOT_ID) {
-		if (current->fsuid != fc->user_id)
+		if (!(fc->flags & FUSE_ALLOW_OTHER) &&
+		    current->fsuid != fc->user_id)
 			return -EACCES;
 	} else if (time_before_eq(jiffies, fi->i_time))
 		return 0;
@@ -430,9 +431,31 @@ static int fuse_permission(struct inode *inode, int mask, struct nameidata *nd)
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
 
-	if (current->fsuid != fc->user_id)
+	if (!(fc->flags & FUSE_ALLOW_OTHER) && current->fsuid != fc->user_id)
 		return -EACCES;
-	else {
+	else if (fc->flags & FUSE_DEFAULT_PERMISSIONS) {
+		int err = generic_permission(inode, mask, NULL);
+
+		/* If permission is denied, try to refresh file
+		   attributes.  This is also needed, because the root
+		   node will at first have no permissions */
+		if (err == -EACCES) {
+		 	err = fuse_do_getattr(inode);
+			if (!err)
+				err = generic_permission(inode, mask, NULL);
+		}
+
+		/* FIXME: Need some mechanism to revoke permissions:
+		   currently if the filesystem suddenly changes the
+		   file mode, we will not be informed about it, and
+		   continue to allow access to the file/directory.
+
+		   This is actually not so grave, since the user can
+		   simply keep access to the file/directory anyway by
+		   keeping it open... */
+
+		return err;
+	} else {
 		int mode = inode->i_mode;
 		if ((mask & MAY_WRITE) && IS_RDONLY(inode) &&
                     (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
@@ -636,6 +659,12 @@ static int fuse_setattr(struct dentry *entry, struct iattr *attr)
 	int err;
 	int is_truncate = 0;
 
+	if (fc->flags & FUSE_DEFAULT_PERMISSIONS) {
+		err = inode_change_ok(inode, attr);
+		if (err)
+			return err;
+	}
+
 	if (attr->ia_valid & ATTR_SIZE) {
 		unsigned long limit;
 		is_truncate = 1;

fs/fuse/file.c

@@ -70,7 +70,7 @@ static int fuse_open(struct inode *inode, struct file *file)
 	else
 		request_send(fc, req);
 	err = req->out.h.error;
-	if (!err)
+	if (!err && !(fc->flags & FUSE_KERNEL_CACHE))
 		invalidate_inode_pages(inode->i_mapping);
 	if (err) {
 		fuse_request_free(ff->release_req);

fs/fuse/fuse_i.h

@@ -21,6 +21,19 @@
 /** If more requests are outstanding, then the operation will block */
 #define FUSE_MAX_OUTSTANDING 10
 
+/** If the FUSE_DEFAULT_PERMISSIONS flag is given, the filesystem
+    module will check permissions based on the file mode.  Otherwise no
+    permission checking is done in the kernel */
+#define FUSE_DEFAULT_PERMISSIONS (1 << 0)
+
+/** If the FUSE_ALLOW_OTHER flag is given, then not only the user
+    doing the mount will be allowed to access the filesystem */
+#define FUSE_ALLOW_OTHER         (1 << 1)
+
+/** If the FUSE_KERNEL_CACHE flag is given, then cached data will not
+    be flushed on open */
+#define FUSE_KERNEL_CACHE        (1 << 2)
+
 /** FUSE inode */
 struct fuse_inode {
 	/** Inode data */
@@ -109,6 +122,9 @@ struct fuse_req {
 	    lists in fuse_conn */
 	struct list_head list;
 
+	/** Entry on the background list */
+	struct list_head bg_entry;
+
 	/** refcount */
 	atomic_t count;
 
@@ -176,15 +192,15 @@ struct fuse_req {
  * unmounted.
  */
 struct fuse_conn {
-	/** The superblock of the mounted filesystem */
-	struct super_block *sb;
-
-	/** The opened client device */
-	struct file *file;
+	/** Reference count */
+	int count;
 
 	/** The user id for this mount */
 	uid_t user_id;
 
+	/** The fuse mount flags for this mount */
+	unsigned flags;
+
 	/** Readers of the connection are waiting on this */
 	wait_queue_head_t waitq;
 
@@ -194,19 +210,32 @@ struct fuse_conn {
 	/** The list of requests being processed */
 	struct list_head processing;
 
+	/** Requests put in the background (RELEASE or any other
+	    interrupted request) */
+	struct list_head background;
+
 	/** Controls the maximum number of outstanding requests */
 	struct semaphore outstanding_sem;
 
 	/** This counts the number of outstanding requests if
 	    outstanding_sem would go negative */
 	unsigned outstanding_debt;
 
+	/** RW semaphore for exclusion with fuse_put_super() */
+	struct rw_semaphore sbput_sem;
+
 	/** The list of unused requests */
 	struct list_head unused_list;
 
 	/** The next unique request id */
 	u64 reqctr;
 
+	/** Mount is active */
+	unsigned mounted : 1;
+
+	/** Connection established */
+	unsigned connected : 1;
+
 	/** Connection failed (version mismatch) */
 	unsigned conn_error : 1;
 
@@ -261,6 +290,7 @@ extern struct file_operations fuse_dev_operations;
  *  - the private_data field of the device file
  *  - the s_fs_info field of the super block
  *  - unused_list, pending, processing lists in fuse_conn
+ *  - background list in fuse_conn
  *  - the unique request ID counter reqctr in fuse_conn
  *  - the sb (super_block) field in fuse_conn
  *  - the file (device file) field in fuse_conn
@@ -371,6 +401,11 @@ void request_send_noreply(struct fuse_conn *fc, struct fuse_req *req);
  */
 void request_send_background(struct fuse_conn *fc, struct fuse_req *req);
 
+/**
+ * Release inodes and file assiciated with background request
+ */
+void fuse_release_background(struct fuse_req *req);
+
 /**
  * Get the attributes of a file
  */