[rfc][patch] fs: dcache remove d_mounted

[Nick Piggin <npiggin@suse.de>]

Hi,

I'd just like to ask you to look at autofs4 in the context of this change.
I don't really know what needs to be considered there. If this is a
generally visible dentry that any other users may mount filesystems on,
then this might be difficult to get working here.

I'm not quite sure what games you're playing here with d_mounted... In the
simplest case we might be able to just remove DCACHE_MOUNTED.

Anyway this would be great if we can make it work so I can replace the
member with d_seq for my path walk patches and not bloat dentry. Can you
take a look please if you have a chance?
--

XXX: breaks autofs4, have to work out what it is doing. We can get a mounted
count if needed by counting the hashtable.
---
 fs/dcache.c            |    1 -
 fs/namespace.c         |   19 +++++++++++++++----
 include/linux/dcache.h |   42 +++++++++++++++++++++---------------------
 3 files changed, 36 insertions(+), 26 deletions(-)

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c
+++ linux-2.6/fs/dcache.c
@@ -1192,7 +1192,6 @@ struct dentry *d_alloc(struct dentry * p
 	dentry->d_sb = NULL;
 	dentry->d_op = NULL;
 	dentry->d_fsdata = NULL;
-	dentry->d_mounted = 0;
 	INIT_HLIST_NODE(&dentry->d_hash);
 	INIT_LIST_HEAD(&dentry->d_lru);
 	INIT_LIST_HEAD(&dentry->d_subdirs);
Index: linux-2.6/fs/namespace.c
===================================================================
--- linux-2.6.orig/fs/namespace.c
+++ linux-2.6/fs/namespace.c
@@ -574,6 +574,15 @@ static void __touch_mnt_namespace(struct
 	}
 }
 
+static void dentry_reset_mounted(struct vfsmount *mnt, struct dentry *dentry)
+{
+	if (!__lookup_mnt(mnt, dentry, 0)) {
+		spin_lock(&dentry->d_lock);
+		dentry->d_flags &= ~DCACHE_MOUNTED;
+		spin_unlock(&dentry->d_lock);
+	}
+}
+
 static void detach_mnt(struct vfsmount *mnt, struct path *old_path)
 {
 	old_path->dentry = mnt->mnt_mountpoint;
@@ -582,7 +591,7 @@ static void detach_mnt(struct vfsmount *
 	mnt->mnt_mountpoint = mnt->mnt_root;
 	list_del_init(&mnt->mnt_hash);
 	list_del_init(&mnt->mnt_child);
-	old_path->dentry->d_mounted--;
+	dentry_reset_mounted(old_path->mnt, old_path->dentry);
 	WARN_ON(mnt->mnt_mounted != 1);
 	mnt->mnt_mounted--;
 }
@@ -591,8 +600,10 @@ void mnt_set_mountpoint(struct vfsmount
 			struct vfsmount *child_mnt)
 {
 	child_mnt->mnt_parent = mntget(mnt);
-	child_mnt->mnt_mountpoint = dget(dentry);
-	dentry->d_mounted++;
+	spin_lock(&dentry->d_lock);
+	child_mnt->mnt_mountpoint = dget_dlock(dentry);
+	dentry->d_flags |= DCACHE_MOUNTED;
+	spin_unlock(&dentry->d_lock);
 }
 
 static void attach_mnt(struct vfsmount *mnt, struct path *path)
@@ -1170,7 +1181,7 @@ void umount_tree(struct vfsmount *mnt, i
 		p->mnt_mounted--;
 		if (p->mnt_parent != p) {
 			p->mnt_parent->mnt_ghosts++;
-			p->mnt_mountpoint->d_mounted--;
+			dentry_reset_mounted(p->mnt_parent, p->mnt_mountpoint);
 		}
 		change_mnt_propagation(p, MS_PRIVATE);
 	}
Index: linux-2.6/include/linux/dcache.h
===================================================================
--- linux-2.6.orig/include/linux/dcache.h
+++ linux-2.6/include/linux/dcache.h
@@ -83,14 +83,13 @@ full_name_hash(const unsigned char *name
 #ifdef CONFIG_64BIT
 #define DNAME_INLINE_LEN_MIN 32 /* 192 bytes */
 #else
-#define DNAME_INLINE_LEN_MIN 40 /* 128 bytes */
+#define DNAME_INLINE_LEN_MIN 44 /* 128 bytes */
 #endif
 
 struct dentry {
 	unsigned int d_count;		/* protected by d_lock */
 	unsigned int d_flags;		/* protected by d_lock */
 	spinlock_t d_lock;		/* per dentry lock */
-	int d_mounted;
 	struct inode *d_inode;		/* Where the name belongs to - NULL is
 					 * negative */
 	/*
@@ -161,30 +160,31 @@ d_iput:		no		no       yes
 
 /* d_flags entries */
 #define DCACHE_AUTOFS_PENDING 0x0001    /* autofs: "under construction" */
-#define DCACHE_NFSFS_RENAMED  0x0002    /* this dentry has been "silly
-					 * renamed" and has to be
-					 * deleted on the last dput()
-					 */
-#define	DCACHE_DISCONNECTED 0x0004
-     /* This dentry is possibly not currently connected to the dcache tree,
-      * in which case its parent will either be itself, or will have this
-      * flag as well.  nfsd will not use a dentry with this bit set, but will
-      * first endeavour to clear the bit either by discovering that it is
-      * connected, or by performing lookup operations.   Any filesystem which
-      * supports nfsd_operations MUST have a lookup function which, if it finds
-      * a directory inode with a DCACHE_DISCONNECTED dentry, will d_move
-      * that dentry into place and return that dentry rather than the passed one,
-      * typically using d_splice_alias.
-      */
+#define DCACHE_NFSFS_RENAMED  0x0002
+     /* this dentry has been "silly renamed" and has to be deleted on the last
+      * dput() */
+
+#define	DCACHE_DISCONNECTED	0x0004
+     /* This dentry is possibly not currently connected to the dcache tree, in
+      * which case its parent will either be itself, or will have this flag as
+      * well.  nfsd will not use a dentry with this bit set, but will first
+      * endeavour to clear the bit either by discovering that it is connected,
+      * or by performing lookup operations.   Any filesystem which supports
+      * nfsd_operations MUST have a lookup function which, if it finds a
+      * directory inode with a DCACHE_DISCONNECTED dentry, will d_move that
+      * dentry into place and return that dentry rather than the passed one,
+      * typically using d_splice_alias. */
 
 #define DCACHE_REFERENCED	0x0008  /* Recently used, don't discard. */
 #define DCACHE_UNHASHED		0x0010	
-
-#define DCACHE_INOTIFY_PARENT_WATCHED	0x0020 /* Parent inode is watched by inotify */
+#define DCACHE_INOTIFY_PARENT_WATCHED 0x0020
+     /* Parent inode is watched by inotify */
 
 #define DCACHE_COOKIE		0x0040	/* For use by dcookie subsystem */
+#define DCACHE_FSNOTIFY_PARENT_WATCHED 0x0080
+     /* Parent inode is watched by some fsnotify listener */
 
-#define DCACHE_FSNOTIFY_PARENT_WATCHED	0x0080 /* Parent inode is watched by some fsnotify listener */
+#define DCACHE_MOUNTED		0x0100	/* is a mountpoint */
 
 extern seqlock_t rename_lock;
 
@@ -349,7 +349,7 @@ extern void dput(struct dentry *);
 
 static inline int d_mountpoint(struct dentry *dentry)
 {
-	return dentry->d_mounted;
+	return dentry->d_flags & DCACHE_MOUNTED;
 }
 
 extern struct vfsmount *lookup_mnt(struct path *);