vfs: new helper - vfs_ustat()

... and bury user_get_super()/statfs_by_dentry() - they are
purely internal now.

Signed-off-by: Al Viro <[e-mail]>

arch/parisc/hpux/sys_hpux.c

···
  */
 static int hpux_ustat(dev_t dev, struct hpux_ustat __user *ubuf)
 {
-	struct super_block *s;
 	struct hpux_ustat tmp;  /* Changed to hpux_ustat */
 	struct kstatfs sbuf;
-	int err = -EINVAL;
-
-	s = user_get_super(dev);
-	if (s == NULL)
-		goto out;
-	err = statfs_by_dentry(s->s_root, &sbuf);
-	drop_super(s);
+	int err = vfs_ustat(dev, &sbuf);
 	if (err)
 		goto out;
 

fs/compat.c

···
  */
 asmlinkage long compat_sys_ustat(unsigned dev, struct compat_ustat __user *u)
 {
-	struct super_block *sb;
 	struct compat_ustat tmp;
 	struct kstatfs sbuf;
-	int err;
-
-	sb = user_get_super(new_decode_dev(dev));
-	if (!sb)
-		return -EINVAL;
-	err = statfs_by_dentry(sb->s_root, &sbuf);
-	drop_super(sb);
+	int err = vfs_ustat(new_decode_dev(dev), &sbuf);
 	if (err)
 		return err;
 

fs/internal.h

···
 extern bool grab_super_passive(struct super_block *sb);
 extern struct dentry *mount_fs(struct file_system_type *,
 			       int, const char *, void *);
+extern struct super_block *user_get_super(dev_t);
 
 /*
  * open.c

fs/statfs.c

···
 #include <linux/statfs.h>
 #include <linux/security.h>
 #include <linux/uaccess.h>
+#include "internal.h"
 
 static int flags_by_mnt(int mnt_flags)
 {
···
 		flags_by_sb(mnt->mnt_sb->s_flags);
 }
 
-int statfs_by_dentry(struct dentry *dentry, struct kstatfs *buf)
+static int statfs_by_dentry(struct dentry *dentry, struct kstatfs *buf)
 {
 	int retval;
 
···
 	return error;
 }
 
-SYSCALL_DEFINE2(ustat, unsigned, dev, struct ustat __user *, ubuf)
+int vfs_ustat(dev_t dev, struct kstatfs *sbuf)
 {
-	struct super_block *s;
-	struct ustat tmp;
-	struct kstatfs sbuf;
+	struct super_block *s = user_get_super(dev);
 	int err;
-
-	s = user_get_super(new_decode_dev(dev));
 	if (!s)
 		return -EINVAL;
 
-	err = statfs_by_dentry(s->s_root, &sbuf);
+	err = statfs_by_dentry(s->s_root, sbuf);
 	drop_super(s);
+	return err;
+}
+
+SYSCALL_DEFINE2(ustat, unsigned, dev, struct ustat __user *, ubuf)
+{
+	struct ustat tmp;
+	struct kstatfs sbuf;
+	int err = vfs_ustat(new_decode_dev(dev), &sbuf);
 	if (err)
 		return err;
 

include/linux/fs.h

···
 extern int vfs_statfs(struct path *, struct kstatfs *);
 extern int user_statfs(const char __user *, struct kstatfs *);
 extern int fd_statfs(int, struct kstatfs *);
-extern int statfs_by_dentry(struct dentry *, struct kstatfs *);
+extern int vfs_ustat(dev_t, struct kstatfs *);
 extern int freeze_super(struct super_block *super);
 extern int thaw_super(struct super_block *super);
 extern bool our_mnt(struct vfsmount *mnt);
···
 extern struct file_system_type *get_fs_type(const char *name);
 extern struct super_block *get_super(struct block_device *);
 extern struct super_block *get_active_super(struct block_device *bdev);
-extern struct super_block *user_get_super(dev_t);
 extern void drop_super(struct super_block *sb);
 extern void iterate_supers(void (*)(struct super_block *, void *), void *);
 extern void iterate_supers_type(struct file_system_type *,