shmem: support RENAME_WHITEOUT

Allocate a dentry, initialize it with a whiteout and hash it in the place
of the old dentry.  Later the old dentry will be moved away and the
whiteout will remain.

i_mutex protects agains concurrent readdir.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Hugh Dickins <hughd@google.com>

1 files changed, 35 insertions, 1 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index cd6fc7590e54..185836ba53ef 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2345,6 +2345,32 @@ static int shmem_exchange(struct inode *old_dir, struct dentry *old_dentry, stru
         return 0;
 }
 
+static int shmem_whiteout(struct inode *old_dir, struct dentry *old_dentry)
+{
+        struct dentry *whiteout;
+        int error;
+
+        whiteout = d_alloc(old_dentry->d_parent, &old_dentry->d_name);
+        if (!whiteout)
+                return -ENOMEM;
+
+        error = shmem_mknod(old_dir, whiteout,
+                            S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV);
+        dput(whiteout);
+        if (error)
+                return error;
+
+        /*
+         * Cheat and hash the whiteout while the old dentry is still in
+         * place, instead of playing games with FS_RENAME_DOES_D_MOVE.
+         *
+         * d_lookup() will consistently find one of them at this point,
+         * not sure which one, but that isn't even important.
+         */
+        d_rehash(whiteout);
+        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
@@ -2356,7 +2382,7 @@ 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 | RENAME_EXCHANGE))
+        if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
                 return -EINVAL;
 
         if (flags & RENAME_EXCHANGE)
@@ -2365,6 +2391,14 @@ static int shmem_rename2(struct inode *old_dir, struct dentry *old_dentry, struc
         if (!simple_empty(new_dentry))
                 return -ENOTEMPTY;
 
+        if (flags & RENAME_WHITEOUT) {
+                int error;
+
+                error = shmem_whiteout(old_dir, old_dentry);
+                if (error)
+                        return error;
+        }
+
         if (new_dentry->d_inode) {
                 (void) shmem_unlink(new_dir, new_dentry);
                 if (they_are_dirs) {