From: Miklos Szeredi <[email protected]>
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 <[email protected]>
---
fs/namespace.c | 34 ++++++++++++++++++++++++++++++++++
include/linux/mount.h | 1 +
2 files changed, 35 insertions(+)
Index: vfs-2.6/fs/namespace.c
===================================================================
--- vfs-2.6.orig/fs/namespace.c 2008-03-26 21:37:06.000000000 +0100
+++ vfs-2.6/fs/namespace.c 2008-03-26 21:37:40.000000000 +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 +60,41 @@ static inline unsigned long hash(struct
#define MNT_WRITER_UNDERFLOW_LIMIT -(1<<16)
+static int mnt_alloc_id(struct vfsmount *mnt)
+{
+ int res;
+
+ retry:
+ spin_lock(&vfsmount_lock);
+ res = ida_get_new(&mnt_id_ida, &mnt->mnt_id);
+ spin_unlock(&vfsmount_lock);
+ if (res == -EAGAIN) {
+ if (ida_pre_get(&mnt_id_ida, GFP_KERNEL))
+ goto retry;
+ res = -ENOMEM;
+ }
+ return res;
+}
+
+static void mnt_free_id(struct vfsmount *mnt)
+{
+ spin_lock(&vfsmount_lock);
+ ida_remove(&mnt_id_ida, mnt->mnt_id);
+ spin_unlock(&vfsmount_lock);
+}
+
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);
@@ -353,6 +386,7 @@ EXPORT_SYMBOL(simple_set_mnt);
void free_vfsmnt(struct vfsmount *mnt)
{
kfree(mnt->mnt_devname);
+ mnt_free_id(mnt);
kmem_cache_free(mnt_cache, mnt);
}
Index: vfs-2.6/include/linux/mount.h
===================================================================
--- vfs-2.6.orig/include/linux/mount.h 2008-03-26 21:37:06.000000000 +0100
+++ vfs-2.6/include/linux/mount.h 2008-03-26 21:37:40.000000000 +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
--
On Wed, Mar 26, 2008 at 10:11:34PM +0100, Miklos Szeredi wrote:
> +static int mnt_alloc_id(struct vfsmount *mnt)
> +{
> + int res;
> +
> + retry:
> + spin_lock(&vfsmount_lock);
> + res = ida_get_new(&mnt_id_ida, &mnt->mnt_id);
> + spin_unlock(&vfsmount_lock);
> + if (res == -EAGAIN) {
> + if (ida_pre_get(&mnt_id_ida, GFP_KERNEL))
> + goto retry;
> + res = -ENOMEM;
> + }
> + return res;
*Ugh*
Why bother with vfsmount_lock here? All allocations are done under
namespace_sem. Moreover, I'd rather replace that 'goto retry' with
a single call of ida_get_new(), since we are serialized anyway.
> @@ -353,6 +386,7 @@ EXPORT_SYMBOL(simple_set_mnt);
> void free_vfsmnt(struct vfsmount *mnt)
> {
> kfree(mnt->mnt_devname);
> + mnt_free_id(mnt);
> kmem_cache_free(mnt_cache, mnt);
> }
... and I'd rather do that earlier, e.g. in umount_tree(). At that point
we (a) have namespace_sem and (b) irrevocably kick the sucker out of
any namespace.
I'd rather minimize banging vfsmount_lock like that...