fs: introduce f_op->mmap_capabilities for nommu mmap support

Since "BDI: Provide backing device capability information [try #3]" the
backing_dev_info structure also provides flags for the kind of mmap
operation available in a nommu environment, which is entirely unrelated
to it's original purpose.

Introduce a new nommu-only file operation to provide this information to
the nommu mmap code instead.  Splitting this from the backing_dev_info
structure allows to remove lots of backing_dev_info instance that aren't
otherwise needed, and entirely gets rid of the concept of providing a
backing_dev_info for a character device.  It also removes the need for
the mtd_inodefs filesystem.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Tejun Heo <tj@kernel.org>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

2 files changed, 9 insertions, 20 deletions

diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c
index bbafbde..f6ab41b 100644
--- a/fs/ramfs/file-nommu.c
+++ b/fs/ramfs/file-nommu.c
@@ -34,7 +34,14 @@ static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 						   unsigned long flags);
 static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);
 
+static unsigned ramfs_mmap_capabilities(struct file *file)
+{
+	return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
+		NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
+}
+
 const struct file_operations ramfs_file_operations = {
+	.mmap_capabilities	= ramfs_mmap_capabilities,
 	.mmap			= ramfs_nommu_mmap,
 	.get_unmapped_area	= ramfs_nommu_get_unmapped_area,
 	.read			= new_sync_read,
diff --git a/fs/ramfs/inode.c b/fs/ramfs/inode.c
index d365b1c..ad4d712 100644
--- a/fs/ramfs/inode.c
+++ b/fs/ramfs/inode.c
@@ -50,14 +50,6 @@ static const struct address_space_operations ramfs_aops = {
 	.set_page_dirty	= __set_page_dirty_no_writeback,
 };
 
-static struct backing_dev_info ramfs_backing_dev_info = {
-	.name		= "ramfs",
-	.ra_pages	= 0,	/* No readahead */
-	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK |
-			  BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
-			  BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP,
-};
-
 struct inode *ramfs_get_inode(struct super_block *sb,
 				const struct inode *dir, umode_t mode, dev_t dev)
 {
@@ -67,7 +59,7 @@ struct inode *ramfs_get_inode(struct super_block *sb,
 		inode->i_ino = get_next_ino();
 		inode_init_owner(inode, dir, mode);
 		inode->i_mapping->a_ops = &ramfs_aops;
-		inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
+		inode->i_mapping->backing_dev_info = &noop_backing_dev_info;
 		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
 		mapping_set_unevictable(inode->i_mapping);
 		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
@@ -267,19 +259,9 @@ static struct file_system_type ramfs_fs_type = {
 int __init init_ramfs_fs(void)
 {
 	static unsigned long once;
-	int err;
 
 	if (test_and_set_bit(0, &once))
 		return 0;
-
-	err = bdi_init(&ramfs_backing_dev_info);
-	if (err)
-		return err;
-
-	err = register_filesystem(&ramfs_fs_type);
-	if (err)
-		bdi_destroy(&ramfs_backing_dev_info);
-
-	return err;
+	return register_filesystem(&ramfs_fs_type);
 }
 fs_initcall(init_ramfs_fs);