[patch 3/7] vfs: mountinfo: add mount ID

[Miklos Szeredi <miklos@szeredi.hu>]

[-- Attachment #1: mountinfo_mnt_id.patch --]
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From: Miklos Szeredi <mszeredi@suse.cz>

Add a unique ID to each vfsmount using the IDR infrastructure.  The
identifiers are reused after the vfsmount is freed.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/namespace.c        |   20 ++++++++++++++++++++
 include/linux/mount.h |    1 +
 2 files changed, 21 insertions(+)

Index: vfs-2.6/fs/namespace.c
===================================================================
--- vfs-2.6.orig/fs/namespace.c	2008-03-27 12:05:55.000000000 +0100
+++ vfs-2.6/fs/namespace.c	2008-03-27 12:06:08.000000000 +0100
@@ -27,6 +27,7 @@
 #include <linux/mount.h>
 #include <linux/ramfs.h>
 #include <linux/log2.h>
+#include <linux/idr.h>
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
 #include "pnode.h"
@@ -39,6 +40,7 @@
 __cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
 
 static int event;
+static DEFINE_IDA(mnt_id_ida);
 
 static struct list_head *mount_hashtable __read_mostly;
 static struct kmem_cache *mnt_cache __read_mostly;
@@ -58,10 +60,26 @@ static inline unsigned long hash(struct 
 
 #define MNT_WRITER_UNDERFLOW_LIMIT -(1<<16)
 
+static int mnt_alloc_id(struct vfsmount *mnt)
+{
+	if (!ida_pre_get(&mnt_id_ida, GFP_KERNEL))
+		return -ENOMEM;
+
+	return ida_get_new_above(&mnt_id_ida, 1, &mnt->mnt_id);
+}
+
 struct vfsmount *alloc_vfsmnt(const char *name)
 {
 	struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
 	if (mnt) {
+		int err;
+
+		err = mnt_alloc_id(mnt);
+		if (err) {
+			kmem_cache_free(mnt_cache, mnt);
+			return NULL;
+		}
+
 		atomic_set(&mnt->mnt_count, 1);
 		INIT_LIST_HEAD(&mnt->mnt_hash);
 		INIT_LIST_HEAD(&mnt->mnt_child);
@@ -866,6 +884,8 @@ void umount_tree(struct vfsmount *mnt, i
 			p->mnt_mountpoint->d_mounted--;
 		}
 		change_mnt_propagation(p, MS_PRIVATE);
+		ida_remove(&mnt_id_ida, p->mnt_id);
+		p->mnt_id = 0;
 	}
 }
 
Index: vfs-2.6/include/linux/mount.h
===================================================================
--- vfs-2.6.orig/include/linux/mount.h	2008-03-27 12:05:55.000000000 +0100
+++ vfs-2.6/include/linux/mount.h	2008-03-27 12:06:08.000000000 +0100
@@ -56,6 +56,7 @@ struct vfsmount {
 	struct list_head mnt_slave;	/* slave list entry */
 	struct vfsmount *mnt_master;	/* slave is on master->mnt_slave_list */
 	struct mnt_namespace *mnt_ns;	/* containing namespace */
+	int mnt_id;			/* mount identifier */
 	/*
 	 * We put mnt_count & mnt_expiry_mark at the end of struct vfsmount
 	 * to let these frequently modified fields in a separate cache line

--