[PATCH] simple_fill_super()

	New libfs.c helper - simple_fill_super().  Abstracted from
nfsd/nfsctl.c, couple of filesystems converted to it (nfsctl, binfmt_misc).

	Function takes an array of triples (name, file_operations, mode),
superblock and value for its ->s_magic.  It acts as fill_super() - populates
superblock or fails.  We get a ramfs-style flat tree - root directory and
a bunch of files in it.

	That animal allows to put together a simple filesystem without
touching any directory-related stuff - now it's as easy as implementing
file_operations for files you want to have and telling what to call them.

fs/binfmt_misc.c

@@ -630,64 +630,20 @@ static struct file_operations bm_status_operations = {
 
 static struct super_operations s_ops = {
 	.statfs		= simple_statfs,
-	.drop_inode	= generic_delete_inode,
 	.clear_inode	= bm_clear_inode,
 };
 
 static int bm_fill_super(struct super_block * sb, void * data, int silent)
 {
-	struct qstr names[2] = {{.name = "status"}, {.name = "register"}};
-	struct inode * inode;
-	struct dentry * dentry[3];
-	int i;
-
-	for (i=0; i<sizeof(names)/sizeof(names[0]); i++) {
-		names[i].len = strlen(names[i].name);
-		names[i].hash = full_name_hash(names[i].name, names[i].len);
-	}
-
-	sb->s_blocksize = PAGE_CACHE_SIZE;
-	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
-	sb->s_magic = 0x42494e4d;
-	sb->s_op = &s_ops;
-
-	inode = bm_get_inode(sb, S_IFDIR | 0755);
-	if (!inode)
-		return -ENOMEM;
-	inode->i_op = &simple_dir_inode_operations;
-	inode->i_fop = &simple_dir_operations;
-	dentry[0] = d_alloc_root(inode);
-	if (!dentry[0]) {
-		iput(inode);
-		return -ENOMEM;
-	}
-	dentry[1] = d_alloc(dentry[0], &names[0]);
-	if (!dentry[1])
-		goto out1;
-	dentry[2] = d_alloc(dentry[0], &names[1]);
-	if (!dentry[2])
-		goto out2;
-	inode = bm_get_inode(sb, S_IFREG | 0644);
-	if (!inode)
-		goto out3;
-	inode->i_fop = &bm_status_operations;
-	d_add(dentry[1], inode);
-	inode = bm_get_inode(sb, S_IFREG | 0400);
-	if (!inode)
-		goto out3;
-	inode->i_fop = &bm_register_operations;
-	d_add(dentry[2], inode);
-
-	sb->s_root = dentry[0];
-	return 0;
-
-out3:
-	dput(dentry[2]);
-out2:
-	dput(dentry[1]);
-out1:
-	dput(dentry[0]);
-	return -ENOMEM;
+	static struct tree_descr bm_files[] = {
+		[1] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
+		[2] = {"register", &bm_register_operations, S_IWUSR},
+		/* last one */ {""}
+	};
+	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
+	if (!err)
+		sb->s_op = &s_ops;
+	return err;
 }
 
 static struct super_block *bm_get_sb(struct file_system_type *fs_type,

fs/libfs.c

@@ -332,3 +332,61 @@ int simple_commit_write(struct file *file, struct page *page,
 	set_page_dirty(page);
 	return 0;
 }
+
+int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files)
+{
+	static struct super_operations s_ops = {statfs:simple_statfs};
+	struct inode *inode;
+	struct dentry *root;
+	struct dentry *dentry;
+	int i;
+
+	s->s_blocksize = PAGE_CACHE_SIZE;
+	s->s_blocksize_bits = PAGE_CACHE_SHIFT;
+	s->s_magic = magic;
+	s->s_op = &s_ops;
+
+	inode = new_inode(s);
+	if (!inode)
+		return -ENOMEM;
+	inode->i_mode = S_IFDIR | 0755;
+	inode->i_uid = inode->i_gid = 0;
+	inode->i_blksize = PAGE_CACHE_SIZE;
+	inode->i_blocks = 0;
+	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+	inode->i_op = &simple_dir_inode_operations;
+	inode->i_fop = &simple_dir_operations;
+	root = d_alloc_root(inode);
+	if (!root) {
+		iput(inode);
+		return -ENOMEM;
+	}
+	for (i = 0; !files->name || files->name[0]; i++, files++) {
+		struct qstr name;
+		if (!files->name)
+			continue;
+		name.name = files->name;
+		name.len = strlen(name.name);
+		name.hash = full_name_hash(name.name, name.len);
+		dentry = d_alloc(root, &name);
+		if (!dentry)
+			goto out;
+		inode = new_inode(s);
+		if (!inode)
+			goto out;
+		inode->i_mode = S_IFREG | files->mode;
+		inode->i_uid = inode->i_gid = 0;
+		inode->i_blksize = PAGE_CACHE_SIZE;
+		inode->i_blocks = 0;
+		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+		inode->i_fop = files->ops;
+		inode->i_ino = i;
+		d_add(dentry, inode);
+	}
+	s->s_root = root;
+	return 0;
+out:
+	d_genocide(root);
+	dput(root);
+	return -ENOMEM;
+}

fs/nfsd/nfsctl.c

@@ -48,7 +48,6 @@ enum {
 	NFSD_List,
 	NFSD_Fh,
 	NFSD_Threads,
-	NFSD_END
 };
 
 /*
@@ -204,22 +203,6 @@ static struct file_operations exports_operations = {
 	.release	= exports_release,
 };
 
-/*
- *	Description of fs contents.
- */
-static struct { char *name; struct file_operations *ops; int mode; } files[] = {
-	[NFSD_Svc] = {".svc", &transaction_ops, S_IWUSR},
-	[NFSD_Add] = {".add", &transaction_ops, S_IWUSR},
-	[NFSD_Del] = {".del", &transaction_ops, S_IWUSR},
-	[NFSD_Export] = {".export", &transaction_ops, S_IWUSR},
-	[NFSD_Unexport] = {".unexport", &transaction_ops, S_IWUSR},
-	[NFSD_Getfd] = {".getfd", &transaction_ops, S_IWUSR|S_IRUSR},
-	[NFSD_Getfs] = {".getfs", &transaction_ops, S_IWUSR|S_IRUSR},
-	[NFSD_List] = {"exports", &exports_operations, S_IRUGO},
-	[NFSD_Fh] = {"filehandle", &transaction_ops, S_IWUSR|S_IRUSR},
-	[NFSD_Threads] = {"threads", &transaction_ops, S_IWUSR|S_IRUSR},
-};
-
 /*----------------------------------------------------------------------------*/
 /*
  * payload - write methods
@@ -431,64 +414,22 @@ static ssize_t write_threads(struct file *file, char *buf, size_t size)
  *	populating the filesystem.
  */
 
-static struct super_operations s_ops = {
-	.statfs		= simple_statfs,
-};
-
 static int nfsd_fill_super(struct super_block * sb, void * data, int silent)
 {
-	struct inode *inode;
-	struct dentry *root;
-	struct dentry *dentry;
-	int i;
-
-	sb->s_blocksize = PAGE_CACHE_SIZE;
-	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
-	sb->s_magic = 0x6e667364;
-	sb->s_op = &s_ops;
-
-	inode = new_inode(sb);
-	if (!inode)
-		return -ENOMEM;
-	inode->i_mode = S_IFDIR | 0755;
-	inode->i_uid = inode->i_gid = 0;
-	inode->i_blksize = PAGE_CACHE_SIZE;
-	inode->i_blocks = 0;
-	inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
-	inode->i_op = &simple_dir_inode_operations;
-	inode->i_fop = &simple_dir_operations;
-	root = d_alloc_root(inode);
-	if (!root) {
-		iput(inode);
-		return -ENOMEM;
-	}
-	for (i = NFSD_Svc; i < NFSD_END; i++) {
-		struct qstr name;
-		name.name = files[i].name;
-		name.len = strlen(name.name);
-		name.hash = full_name_hash(name.name, name.len);
-		dentry = d_alloc(root, &name);
-		if (!dentry)
-			goto out;
-		inode = new_inode(sb);
-		if (!inode)
-			goto out;
-		inode->i_mode = S_IFREG | files[i].mode;
-		inode->i_uid = inode->i_gid = 0;
-		inode->i_blksize = PAGE_CACHE_SIZE;
-		inode->i_blocks = 0;
-		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
-		inode->i_fop = files[i].ops;
-		inode->i_ino = i;
-		d_add(dentry, inode);
-	}
-	sb->s_root = root;
-	return 0;
-
-out:
-	d_genocide(root);
-	dput(root);
-	return -ENOMEM;
+	static struct tree_descr nfsd_files[] = {
+		[NFSD_Svc] = {".svc", &transaction_ops, S_IWUSR},
+		[NFSD_Add] = {".add", &transaction_ops, S_IWUSR},
+		[NFSD_Del] = {".del", &transaction_ops, S_IWUSR},
+		[NFSD_Export] = {".export", &transaction_ops, S_IWUSR},
+		[NFSD_Unexport] = {".unexport", &transaction_ops, S_IWUSR},
+		[NFSD_Getfd] = {".getfd", &transaction_ops, S_IWUSR|S_IRUSR},
+		[NFSD_Getfs] = {".getfs", &transaction_ops, S_IWUSR|S_IRUSR},
+		[NFSD_List] = {"exports", &exports_operations, S_IRUGO},
+		[NFSD_Fh] = {"filehandle", &transaction_ops, S_IWUSR|S_IRUSR},
+		[NFSD_Threads] = {"threads", &transaction_ops, S_IWUSR|S_IRUSR},
+		/* last one */ {""}
+	};
+	return simple_fill_super(sb, 0x6e667364, nfsd_files);
 }
 
 static struct super_block *nfsd_get_sb(struct file_system_type *fs_type,

include/linux/fs.h

@@ -1292,6 +1292,8 @@ extern struct dentry *simple_lookup(struct inode *, struct dentry *);
 extern ssize_t generic_read_dir(struct file *, char *, size_t, loff_t *);
 extern struct file_operations simple_dir_operations;
 extern struct inode_operations simple_dir_inode_operations;
+struct tree_descr { char *name; struct file_operations *ops; int mode; };
+extern int simple_fill_super(struct super_block *, int, struct tree_descr *);
 
 #ifdef CONFIG_BLK_DEV_INITRD
 extern unsigned int real_root_dev;

kernel/ksyms.c

@@ -313,6 +313,7 @@ EXPORT_SYMBOL(simple_readpage);
 EXPORT_SYMBOL(simple_prepare_write);
 EXPORT_SYMBOL(simple_commit_write);
 EXPORT_SYMBOL(simple_empty);
+EXPORT_SYMBOL(simple_fill_super);
 EXPORT_SYMBOL(fd_install);
 EXPORT_SYMBOL(put_unused_fd);
 EXPORT_SYMBOL(get_sb_bdev);