shmem: support RENAME_EXCHANGE

This is really simple in tmpfs since the VFS already takes care of
shuffling the dentries.  Just adjust nlink on parent directories and touch
c & mtimes.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 26 insertions, 1 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index fe959181f995..0f018002dd64 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2048,6 +2048,28 @@ static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
         return shmem_unlink(dir, dentry);
 }
 
+static int shmem_exchange(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, struct dentry *new_dentry)
+{
+        bool old_is_dir = S_ISDIR(old_dentry->d_inode->i_mode);
+        bool new_is_dir = S_ISDIR(new_dentry->d_inode->i_mode);
+
+        if (old_dir != new_dir && old_is_dir != new_is_dir) {
+                if (old_is_dir) {
+                        drop_nlink(old_dir);
+                        inc_nlink(new_dir);
+                } else {
+                        drop_nlink(new_dir);
+                        inc_nlink(old_dir);
+                }
+        }
+        old_dir->i_ctime = old_dir->i_mtime =
+        new_dir->i_ctime = new_dir->i_mtime =
+        old_dentry->d_inode->i_ctime =
+        new_dentry->d_inode->i_ctime = CURRENT_TIME;
+
+        return 0;
+}
+
 /*
  * The VFS layer already does all the dentry stuff for rename,
  * we just have to decrement the usage count for the target if
@@ -2059,9 +2081,12 @@ static int shmem_rename2(struct inode *old_dir, struct dentry *old_dentry, struc
         struct inode *inode = old_dentry->d_inode;
         int they_are_dirs = S_ISDIR(inode->i_mode);
 
-        if (flags & ~(RENAME_NOREPLACE))
+        if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
                 return -EINVAL;
 
+        if (flags & RENAME_EXCHANGE)
+                return shmem_exchange(old_dir, old_dentry, new_dir, new_dentry);
+
         if (!simple_empty(new_dentry))
                 return -ENOTEMPTY;