Re: [RFC PATCH 2/4] Mount changes to support union mount.
On Wed, Jun 20, 2007 at 02:23:30PM +0530, Bharata B Rao wrote:
> (replying from a different ID as you didn't copy me on reply)
>
> On 6/20/07, Jan Blunck <[EMAIL PROTECTED]> wrote:
> >On Wed, 20 Jun 2007 11:22:41 +0530, Bharata B Rao wrote:
> >
> >> +/*
> >> + * When propagating mount events to peer group, this is called under
> >> + * vfsmount_lock. Hence using GFP_ATOMIC for kmalloc here.
> >> + * TODO: Can we use a separate kmem cache for union_mount ?
> >> + */
> >> +struct union_mount *alloc_union_mount(struct vfsmount *src_mnt,
> >> + struct dentry *src_dentry, struct vfsmount *dst_mnt,
> >> + struct dentry *dst_dentry)
> >> +{
> >> + struct union_mount *u;
> >> + u = kmalloc(sizeof(struct union_mount), GFP_ATOMIC);
> >> + if (!u)
> >> + return u;
> >> + u->dst_mnt = mntget(dst_mnt);
> >> + u->dst_dentry = dget(dst_dentry);
> >> + u->src_mnt = src_mnt;
> >> + u->src_dentry = dget(src_dentry);
> >> + INIT_LIST_HEAD(&u->hash);
> >> + INIT_LIST_HEAD(&u->list);
> >> + return u;
> >> +}
> >
> >Hmm, you pin the dentries in memory until umount. This isn't good. Besides
> >that this doesn't work with file systems that do invalidate their
> >dentries. The file system must have a chance to replace the dentry in the
> >union structure.
>
> Yes, both top level and next level dentries are pinned until umount of
> the upper layer. I was thinking if we could prune these from
> prune_dcache(). What do you think ?
>
> Ok, I haven't thought about filesystem invalidating the dentries. Yet
> to understand the dentry invalidation, but would filesystem invalidate
> an inuse dentry ?
NFS, and quite possibly other network/cluster filesystems can encounter all
sort of odd conditions where the dentry might change, no?
Josef "Jeff" Sipek.
--
Hegh QaQ law'
quvHa'ghach QaQ puS
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Re: [RFC PATCH 2/4] Mount changes to support union mount.
(replying from a different ID as you didn't copy me on reply)
On 6/20/07, Jan Blunck <[EMAIL PROTECTED]> wrote:
On Wed, 20 Jun 2007 11:22:41 +0530, Bharata B Rao wrote:
> +/*
> + * When propagating mount events to peer group, this is called under
> + * vfsmount_lock. Hence using GFP_ATOMIC for kmalloc here.
> + * TODO: Can we use a separate kmem cache for union_mount ?
> + */
> +struct union_mount *alloc_union_mount(struct vfsmount *src_mnt,
> + struct dentry *src_dentry, struct vfsmount *dst_mnt,
> + struct dentry *dst_dentry)
> +{
> + struct union_mount *u;
> + u = kmalloc(sizeof(struct union_mount), GFP_ATOMIC);
> + if (!u)
> + return u;
> + u->dst_mnt = mntget(dst_mnt);
> + u->dst_dentry = dget(dst_dentry);
> + u->src_mnt = src_mnt;
> + u->src_dentry = dget(src_dentry);
> + INIT_LIST_HEAD(&u->hash);
> + INIT_LIST_HEAD(&u->list);
> + return u;
> +}
Hmm, you pin the dentries in memory until umount. This isn't good. Besides
that this doesn't work with file systems that do invalidate their
dentries. The file system must have a chance to replace the dentry in the
union structure.
Yes, both top level and next level dentries are pinned until umount of
the upper layer. I was thinking if we could prune these from
prune_dcache(). What do you think ?
Ok, I haven't thought about filesystem invalidating the dentries. Yet
to understand the dentry invalidation, but would filesystem invalidate
an inuse dentry ?
Regards,
Bharata.
--
"Men come and go but mountains remain" -- Ruskin Bond.
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Re: [RFC PATCH 2/4] Mount changes to support union mount.
On Wed, 20 Jun 2007 11:22:41 +0530, Bharata B Rao wrote:
> +/*
> + * When propagating mount events to peer group, this is called under
> + * vfsmount_lock. Hence using GFP_ATOMIC for kmalloc here.
> + * TODO: Can we use a separate kmem cache for union_mount ?
> + */
> +struct union_mount *alloc_union_mount(struct vfsmount *src_mnt,
> + struct dentry *src_dentry, struct vfsmount *dst_mnt,
> + struct dentry *dst_dentry)
> +{
> + struct union_mount *u;
> + u = kmalloc(sizeof(struct union_mount), GFP_ATOMIC);
> + if (!u)
> + return u;
> + u->dst_mnt = mntget(dst_mnt);
> + u->dst_dentry = dget(dst_dentry);
> + u->src_mnt = src_mnt;
> + u->src_dentry = dget(src_dentry);
> + INIT_LIST_HEAD(&u->hash);
> + INIT_LIST_HEAD(&u->list);
> + return u;
> +}
Hmm, you pin the dentries in memory until umount. This isn't good. Besides
that this doesn't work with file systems that do invalidate their
dentries. The file system must have a chance to replace the dentry in the
union structure.
Jan
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[RFC PATCH 2/4] Mount changes to support union mount.
From: Bharata B Rao <[EMAIL PROTECTED]>
Subject: Mount changes to support union mount.
Adds union mount support.
This patch adds a new mount type for union mount (MNT_UNION) and changes
the mount path to build a union stack during mount. The routines for
supporting the creation, traversal and destruction of union stacks are
also included here.
Signed-off-by: Bharata B Rao <[EMAIL PROTECTED]>
---
fs/namespace.c| 164 ++
include/linux/fs.h|1
include/linux/mount.h | 17 +
3 files changed, 172 insertions(+), 10 deletions(-)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -35,6 +35,7 @@ __cacheline_aligned_in_smp DEFINE_SPINLO
static int event;
static struct list_head *mount_hashtable __read_mostly;
+static struct list_head *union_mount_hashtable;
static int hash_mask __read_mostly, hash_bits __read_mostly;
static struct kmem_cache *mnt_cache __read_mostly;
static struct rw_semaphore namespace_sem;
@@ -54,6 +55,89 @@ static inline unsigned long hash(struct
return tmp & hash_mask;
}
+/* Must be called with vfsmount_lock held */
+static struct union_mount *find_union_mount(struct vfsmount *mnt,
+ struct dentry *dentry)
+{
+ struct list_head *head;
+ struct union_mount *u;
+
+ if (!IS_MNT_UNION(mnt))
+ return NULL;
+
+ head = union_mount_hashtable + hash(mnt, dentry);
+ list_for_each_entry(u, head, hash)
+ if (u->src_mnt == mnt && u->src_dentry == dentry)
+ return u;
+ return NULL;
+}
+
+/*
+ * When propagating mount events to peer group, this is called under
+ * vfsmount_lock. Hence using GFP_ATOMIC for kmalloc here.
+ * TODO: Can we use a separate kmem cache for union_mount ?
+ */
+struct union_mount *alloc_union_mount(struct vfsmount *src_mnt,
+ struct dentry *src_dentry, struct vfsmount *dst_mnt,
+ struct dentry *dst_dentry)
+{
+ struct union_mount *u;
+ u = kmalloc(sizeof(struct union_mount), GFP_ATOMIC);
+ if (!u)
+ return u;
+ u->dst_mnt = mntget(dst_mnt);
+ u->dst_dentry = dget(dst_dentry);
+ u->src_mnt = src_mnt;
+ u->src_dentry = dget(src_dentry);
+ INIT_LIST_HEAD(&u->hash);
+ INIT_LIST_HEAD(&u->list);
+ return u;
+}
+
+/* Must be called with vfsmount_lock held */
+void attach_mnt_union(struct union_mount *u)
+{
+ if (!u)
+ return;
+
+ list_add_tail(&u->hash, union_mount_hashtable +
+ hash(u->src_mnt, u->src_dentry));
+ list_add_tail(&u->list, &u->src_mnt->mnt_union);
+}
+
+/*
+ * Finds the next (vfsmount, dentry) in the union stack. If found, returns
+ * it via @nd and returns true. Else doesn't modify @nd, but returns false.
+ */
+int next_union_mount(struct nameidata *nd)
+{
+ struct union_mount *u;
+
+ spin_lock(&vfsmount_lock);
+ u = find_union_mount(nd->mnt, nd->dentry);
+ spin_unlock(&vfsmount_lock);
+ if (u) {
+ nd->mnt = u->dst_mnt;
+ nd->dentry = u->dst_dentry;
+ return 1;
+ }
+ return 0;
+}
+
+/* Check if next element of the union stack exists. @nd isn't modified. */
+int next_union_mount_exists(struct vfsmount *mnt, struct dentry *dentry)
+{
+ struct union_mount *u;
+
+ spin_lock(&vfsmount_lock);
+ u = find_union_mount(mnt, dentry);
+ spin_unlock(&vfsmount_lock);
+ if (u)
+ return 1;
+ else
+ return 0;
+}
+
struct vfsmount *alloc_vfsmnt(const char *name)
{
struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
@@ -67,6 +151,7 @@ struct vfsmount *alloc_vfsmnt(const char
INIT_LIST_HEAD(&mnt->mnt_share);
INIT_LIST_HEAD(&mnt->mnt_slave_list);
INIT_LIST_HEAD(&mnt->mnt_slave);
+ INIT_LIST_HEAD(&mnt->mnt_union);
if (name) {
int size = strlen(name) + 1;
char *newname = kmalloc(size, GFP_KERNEL);
@@ -173,18 +258,20 @@ void mnt_set_mountpoint(struct vfsmount
dentry->d_mounted++;
}
-static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
+static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd,
+ struct union_mount *u)
{
mnt_set_mountpoint(nd->mnt, nd->dentry, mnt);
list_add_tail(&mnt->mnt_hash, mount_hashtable +
hash(nd->mnt, nd->dentry));
list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
+ attach_mnt_union(u);
}
/*
* the caller must hold vfsmount_lock
*/
-static void commit_tree(struct vfsmount *mnt)
+static void commit_tree(struct vfsmount *mnt, struct union_mount *u)
{
struct vfsmount *parent = mnt->mnt_parent;
struct vfsmount *m;
@@ -201,6 +288,7 @@ static void commit_tree(struct vfsmount
list_add_tail(&mnt->mnt_hash, mount_hashtable +
