Why do fs outside regular namespace clear DCACHE_UNHASHED?

[Nick Piggin <npiggin@suse.de>]

Please humour a relative vfs/procfs newbie... Why do filesystems insist that
a dentry must be !DCACHE_UNHASHED in order to work in /proc/pid/fd/? I can't
find the code that checks this, and pipefs fds for example _seems_ to work in
proc/pid with this patch applied...


---
 fs/anon_inodes.c |   16 ----------------
 fs/pipe.c        |   18 ------------------
 net/socket.c     |   19 -------------------
 3 files changed, 53 deletions(-)

Index: linux-2.6/fs/pipe.c
===================================================================
--- linux-2.6.orig/fs/pipe.c
+++ linux-2.6/fs/pipe.c
@@ -873,17 +873,6 @@ void free_pipe_info(struct inode *inode)
 }
 
 static struct vfsmount *pipe_mnt __read_mostly;
-static int pipefs_delete_dentry(struct dentry *dentry)
-{
-	/*
-	 * At creation time, we pretended this dentry was hashed
-	 * (by clearing DCACHE_UNHASHED bit in d_flags)
-	 * At delete time, we restore the truth : not hashed.
-	 * (so that dput() can proceed correctly)
-	 */
-	dentry->d_flags |= DCACHE_UNHASHED;
-	return 0;
-}
 
 /*
  * pipefs_dname() is called from d_path().
@@ -895,7 +884,6 @@ static char *pipefs_dname(struct dentry
 }
 
 static const struct dentry_operations pipefs_dentry_operations = {
-	.d_delete	= pipefs_delete_dentry,
 	.d_dname	= pipefs_dname,
 };
 
@@ -955,12 +943,6 @@ struct file *create_write_pipe(int flags
 		goto err_inode;
 
 	dentry->d_op = &pipefs_dentry_operations;
-	/*
-	 * We dont want to publish this dentry into global dentry hash table.
-	 * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
-	 * This permits a working /proc/$pid/fd/XXX on pipes
-	 */
-	dentry->d_flags &= ~DCACHE_UNHASHED;
 	d_instantiate(dentry, inode);
 
 	err = -ENFILE;
Index: linux-2.6/net/socket.c
===================================================================
--- linux-2.6.orig/net/socket.c
+++ linux-2.6/net/socket.c
@@ -307,18 +307,6 @@ static struct file_system_type sock_fs_t
 	.kill_sb =	kill_anon_super,
 };
 
-static int sockfs_delete_dentry(struct dentry *dentry)
-{
-	/*
-	 * At creation time, we pretended this dentry was hashed
-	 * (by clearing DCACHE_UNHASHED bit in d_flags)
-	 * At delete time, we restore the truth : not hashed.
-	 * (so that dput() can proceed correctly)
-	 */
-	dentry->d_flags |= DCACHE_UNHASHED;
-	return 0;
-}
-
 /*
  * sockfs_dname() is called from d_path().
  */
@@ -329,7 +317,6 @@ static char *sockfs_dname(struct dentry
 }
 
 static const struct dentry_operations sockfs_dentry_operations = {
-	.d_delete = sockfs_delete_dentry,
 	.d_dname  = sockfs_dname,
 };
 
@@ -378,12 +365,6 @@ static int sock_attach_fd(struct socket
 		return -ENOMEM;
 
 	dentry->d_op = &sockfs_dentry_operations;
-	/*
-	 * We dont want to push this dentry into global dentry hash table.
-	 * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
-	 * This permits a working /proc/$pid/fd/XXX on sockets
-	 */
-	dentry->d_flags &= ~DCACHE_UNHASHED;
 	d_instantiate(dentry, SOCK_INODE(sock));
 
 	sock->file = file;
Index: linux-2.6/fs/anon_inodes.c
===================================================================
--- linux-2.6.orig/fs/anon_inodes.c
+++ linux-2.6/fs/anon_inodes.c
@@ -33,24 +33,11 @@ static int anon_inodefs_get_sb(struct fi
 			     mnt);
 }
 
-static int anon_inodefs_delete_dentry(struct dentry *dentry)
-{
-	/*
-	 * We faked vfs to believe the dentry was hashed when we created it.
-	 * Now we restore the flag so that dput() will work correctly.
-	 */
-	dentry->d_flags |= DCACHE_UNHASHED;
-	return 1;
-}
-
 static struct file_system_type anon_inode_fs_type = {
 	.name		= "anon_inodefs",
 	.get_sb		= anon_inodefs_get_sb,
 	.kill_sb	= kill_anon_super,
 };
-static const struct dentry_operations anon_inodefs_dentry_operations = {
-	.d_delete	= anon_inodefs_delete_dentry,
-};
 
 /**
  * anon_inode_getfd - creates a new file instance by hooking it up to an
@@ -106,9 +93,6 @@ int anon_inode_getfd(const char *name, c
 	 */
 	atomic_inc(&anon_inode_inode->i_count);
 
-	dentry->d_op = &anon_inodefs_dentry_operations;
-	/* Do not publish this dentry inside the global dentry hash table */
-	dentry->d_flags &= ~DCACHE_UNHASHED;
 	d_instantiate(dentry, anon_inode_inode);
 
 	error = -ENFILE;