fuse: add list of writable files to fuse_inode

Each WRITE request must carry a valid file descriptor.  When a page is written
back from a memory mapping, the file through which the page was dirtied is not
available, so a new mechananism is needed to find a suitable file in
->writepage(s).

A list of fuse_files is added to fuse_inode.  The file is removed from the
list in fuse_release().

This patch is in preparation for writable mmap support.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fuse/file.c

@@ -56,6 +56,7 @@ struct fuse_file *fuse_file_alloc(void)
 			kfree(ff);
 			ff = NULL;
 		}
+		INIT_LIST_HEAD(&ff->write_entry);
 		atomic_set(&ff->count, 0);
 	}
 	return ff;
@@ -150,12 +151,18 @@ int fuse_release_common(struct inode *inode, struct file *file, int isdir)
 {
 	struct fuse_file *ff = file->private_data;
 	if (ff) {
+		struct fuse_conn *fc = get_fuse_conn(inode);
+
 		fuse_release_fill(ff, get_node_id(inode), file->f_flags,
 				  isdir ? FUSE_RELEASEDIR : FUSE_RELEASE);
 
 		/* Hold vfsmount and dentry until release is finished */
 		ff->reserved_req->vfsmount = mntget(file->f_path.mnt);
 		ff->reserved_req->dentry = dget(file->f_path.dentry);
+
+		spin_lock(&fc->lock);
+		list_del(&ff->write_entry);
+		spin_unlock(&fc->lock);
 		/*
 		 * Normally this will send the RELEASE request,
 		 * however if some asynchronous READ or WRITE requests

fs/fuse/fuse_i.h

@@ -70,6 +70,9 @@ struct fuse_inode {
 
 	/** Version of last attribute change */
 	u64 attr_version;
+
+	/** Files usable in writepage.  Protected by fc->lock */
+	struct list_head write_files;
 };
 
 /** FUSE specific file data */
@@ -82,6 +85,9 @@ struct fuse_file {
 
 	/** Refcount */
 	atomic_t count;
+
+	/** Entry on inode's write_files list */
+	struct list_head write_entry;
 };
 
 /** One input argument of a request */

fs/fuse/inode.c

@@ -56,6 +56,7 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
 	fi->i_time = 0;
 	fi->nodeid = 0;
 	fi->nlookup = 0;
+	INIT_LIST_HEAD(&fi->write_files);
 	fi->forget_req = fuse_request_alloc();
 	if (!fi->forget_req) {
 		kmem_cache_free(fuse_inode_cachep, inode);
@@ -68,6 +69,7 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
 static void fuse_destroy_inode(struct inode *inode)
 {
 	struct fuse_inode *fi = get_fuse_inode(inode);
+	BUG_ON(!list_empty(&fi->write_files));
 	if (fi->forget_req)
 		fuse_request_free(fi->forget_req);
 	kmem_cache_free(fuse_inode_cachep, inode);