[PATCH] Fix the setting of file->f_ra on block-special files

We need to set file->f_ra _after_ calling blkdev_open(), when inode->i_mapping
points at the right thing.  And we need to get it from
inode->i_mapping->host->i_mapping too, which represents the underlying device.

Also, don't test for null file->f_mapping in the O_DIRECT checks.
Signed-off-by: Andrew Morton <akpm@osdl.org>

fs/open.c

@@ -790,7 +790,6 @@ struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags)
 	}
 
 	f->f_mapping = inode->i_mapping;
-	file_ra_state_init(&f->f_ra, f->f_mapping);
 	f->f_dentry = dentry;
 	f->f_vfsmnt = mnt;
 	f->f_pos = 0;
@@ -804,10 +803,11 @@ struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags)
 	}
 	f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 
+	file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);
+
 	/* NB: we're sure to have correct a_ops only after f_op->open */
 	if (f->f_flags & O_DIRECT) {
-		if (!f->f_mapping || !f->f_mapping->a_ops ||
-			!f->f_mapping->a_ops->direct_IO) {
+		if (!f->f_mapping->a_ops || !f->f_mapping->a_ops->direct_IO) {
 			fput(f);
 			f = ERR_PTR(-EINVAL);
 		}