Re: [RFC][PATCH 7/14] Union-mount mounting
On Tue, May 15, 2007 at 09:29:39AM +0200, Jan Engelhardt wrote:
>
> On May 14 2007 15:11, Bharata B Rao wrote:
> >
> >TODO: bind and move mounts aren't yet supported with union mounts.
>
> Are the semantics already set?
Not yet.
>
> >@@ -294,6 +294,10 @@ static struct vfsmount *clone_mnt(struct
> > if (!mnt)
> > goto alloc_failed;
> >
> >+/*
> >+ * As of now, cloning of union mounted mnt isn't permitted.
> >+ */
> >+BUG_ON(mnt->mnt_flags & MNT_UNION);
>
> One, please avoid BUG_ONs. Now I am not sure if clone_mnt is called
> as part of kthread creation when CLONE_FS is it. If so, get rid of
> this one real fast. Also see chunk "@@ -1031,.. @@ do_loopback"
> below.
Looks like not CLONE_FS but CLONE_NEWNS ends up calling clone_mnt.
>
> if(mnt->mnt_flags & MNT_UNION)
> goto return_einval;
>
> or something.
Will do this for now, but eventually we need to get this working sanely anyway.
>
> >+#ifdef CONFIG_UNION_MOUNT
> >+struct union_info *uinfo = NULL;
> >+#endif
> >
> > retval = security_sb_umount(mnt, flags);
> > if (retval)
> >@@ -685,6 +696,14 @@ static int do_umount(struct vfsmount *mn
> > }
> >
> > down_write(&namespace_sem);
> >+#ifdef CONFIG_UNION_MOUNT
> >+/*
> >+ * Grab a reference to the union_info which gets detached
> >+ * from the dentries in release_mounts().
> >+ */
> >+if (mnt->mnt_flags & MNT_UNION)
> >+uinfo = union_lock_and_get(mnt->mnt_root);
> >+#endif
> > spin_lock(&vfsmount_lock);
> > event++;
> >
> >@@ -699,6 +718,15 @@ static int do_umount(struct vfsmount *mn
> > security_sb_umount_busy(mnt);
> > up_write(&namespace_sem);
> > release_mounts(&umount_list);
> >+#ifdef CONFIG_UNION_MOUNT
> >+if (uinfo) {
> >+if (atomic_read(&uinfo->u_count) == 1)
> >+/* We are the last user of this union_info */
> >+union_release(uinfo);
> >+else
> >+union_put_and_unlock(uinfo);
> >+}
> >+#endif
> > return retval;
> > }
> >
>
> Is it feasible to do with with some less #if/#endif magic?:
>
Will try. We need union_info here which is available only with
CONFIG_UNION_MOUNT.
> >@@ -1031,6 +1070,15 @@ static int do_loopback(struct nameidata
> > if (err)
> > return err;
> >
> >+/*
> >+ * bind mounting to or from union mounts is not supported
> >+ */
> >+err = -EINVAL;
> >+if (nd->mnt->mnt_flags & MNT_UNION)
> >+goto out_unlocked;
> >+if (old_nd.mnt->mnt_flags & MNT_UNION)
> >+goto out_unlocked;
> >+
>
> Do the same in clone_mnt.
>
> > down_write(&namespace_sem);
> > err = -EINVAL;
> > if (IS_MNT_UNBINDABLE(old_nd.mnt))
> >@@ -1064,6 +1112,7 @@ static int do_loopback(struct nameidata
> >
> > out:
> > up_write(&namespace_sem);
> >+out_unlocked:
> > path_release(&old_nd);
> > return err;
> > }
>
> >+++ b/include/linux/fs.h
> >@@ -1984,6 +1984,9 @@ static inline ino_t parent_ino(struct de
> > /* kernel/fork.c */
> > extern int unshare_files(void);
> >
> >+/* fs/union.c */
> >+#include
> >+
> > /* Transaction based IO helpers */
> >
> > /*
>
> This raises a big eyebrow. If linux/fs.h can compile without the
> inclusion of linux/union.h, do not put linux/union.h in fs.h.
>
Ok, better to include union.h in the appropriate .c file which needs it.
> >+#ifdef CONFIG_UNION_MOUNT
> >+
> >+#include
> >+
> >+/* namespace stuff used at mount time */
> >+extern void attach_mnt_union(struct vfsmount *, struct nameidata *);
> >+extern void detach_mnt_union(struct vfsmount *, struct path *);
>
> You do not need that #include I suppose. Just predeclare the structs.
>
> struct path;
> struct vfsmount;
> extern void ...
>
> Saves us the "compiler slurps in so many .h files" problem.
Sure. And thanks for the review.
Regards,
Bharata.
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Re: [RFC][PATCH 7/14] Union-mount mounting
On May 14 2007 15:11, Bharata B Rao wrote:
>
>TODO: bind and move mounts aren't yet supported with union mounts.
Are the semantics already set?
>@@ -294,6 +294,10 @@ static struct vfsmount *clone_mnt(struct
> if (!mnt)
> goto alloc_failed;
>
>+ /*
>+ * As of now, cloning of union mounted mnt isn't permitted.
>+ */
>+ BUG_ON(mnt->mnt_flags & MNT_UNION);
One, please avoid BUG_ONs. Now I am not sure if clone_mnt is called
as part of kthread creation when CLONE_FS is it. If so, get rid of
this one real fast. Also see chunk "@@ -1031,.. @@ do_loopback"
below.
if(mnt->mnt_flags & MNT_UNION)
goto return_einval;
or something.
>+#ifdef CONFIG_UNION_MOUNT
>+ struct union_info *uinfo = NULL;
>+#endif
>
> retval = security_sb_umount(mnt, flags);
> if (retval)
>@@ -685,6 +696,14 @@ static int do_umount(struct vfsmount *mn
> }
>
> down_write(&namespace_sem);
>+#ifdef CONFIG_UNION_MOUNT
>+ /*
>+ * Grab a reference to the union_info which gets detached
>+ * from the dentries in release_mounts().
>+ */
>+ if (mnt->mnt_flags & MNT_UNION)
>+ uinfo = union_lock_and_get(mnt->mnt_root);
>+#endif
> spin_lock(&vfsmount_lock);
> event++;
>
>@@ -699,6 +718,15 @@ static int do_umount(struct vfsmount *mn
> security_sb_umount_busy(mnt);
> up_write(&namespace_sem);
> release_mounts(&umount_list);
>+#ifdef CONFIG_UNION_MOUNT
>+ if (uinfo) {
>+ if (atomic_read(&uinfo->u_count) == 1)
>+ /* We are the last user of this union_info */
>+ union_release(uinfo);
>+ else
>+ union_put_and_unlock(uinfo);
>+ }
>+#endif
> return retval;
> }
>
Is it feasible to do with with some less #if/#endif magic?:
>@@ -1031,6 +1070,15 @@ static int do_loopback(struct nameidata
> if (err)
> return err;
>
>+ /*
>+ * bind mounting to or from union mounts is not supported
>+ */
>+ err = -EINVAL;
>+ if (nd->mnt->mnt_flags & MNT_UNION)
>+ goto out_unlocked;
>+ if (old_nd.mnt->mnt_flags & MNT_UNION)
>+ goto out_unlocked;
>+
Do the same in clone_mnt.
> down_write(&namespace_sem);
> err = -EINVAL;
> if (IS_MNT_UNBINDABLE(old_nd.mnt))
>@@ -1064,6 +1112,7 @@ static int do_loopback(struct nameidata
>
> out:
> up_write(&namespace_sem);
>+out_unlocked:
> path_release(&old_nd);
> return err;
> }
>+++ b/include/linux/fs.h
>@@ -1984,6 +1984,9 @@ static inline ino_t parent_ino(struct de
> /* kernel/fork.c */
> extern int unshare_files(void);
>
>+/* fs/union.c */
>+#include
>+
> /* Transaction based IO helpers */
>
> /*
This raises a big eyebrow. If linux/fs.h can compile without the
inclusion of linux/union.h, do not put linux/union.h in fs.h.
>+#ifdef CONFIG_UNION_MOUNT
>+
>+#include
>+
>+/* namespace stuff used at mount time */
>+extern void attach_mnt_union(struct vfsmount *, struct nameidata *);
>+extern void detach_mnt_union(struct vfsmount *, struct path *);
You do not need that #include I suppose. Just predeclare the structs.
struct path;
struct vfsmount;
extern void ...
Saves us the "compiler slurps in so many .h files" problem.
Jan
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[RFC][PATCH 7/14] Union-mount mounting
From: Jan Blunck <[EMAIL PROTECTED]>
Subject: Union-mount mounting
Adds union mount support to mount() and umount() system calls.
Sets up the union stack during mount and destroys it during unmount.
TODO: bind and move mounts aren't yet supported with union mounts.
Signed-off-by: Jan Blunck <[EMAIL PROTECTED]>
Signed-off-by: Bharata B Rao <[EMAIL PROTECTED]>
---
fs/namespace.c| 90 ++
fs/union.c| 71 +++
include/linux/fs.h|3 +
include/linux/union.h | 33 ++
4 files changed, 190 insertions(+), 7 deletions(-)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -169,7 +169,7 @@ void mnt_set_mountpoint(struct vfsmount
struct vfsmount *child_mnt)
{
child_mnt->mnt_parent = mntget(mnt);
- child_mnt->mnt_mountpoint = dget(dentry);
+ child_mnt->mnt_mountpoint = __dget(dentry);
dentry->d_mounted++;
}
@@ -294,6 +294,10 @@ static struct vfsmount *clone_mnt(struct
if (!mnt)
goto alloc_failed;
+ /*
+* As of now, cloning of union mounted mnt isn't permitted.
+*/
+ BUG_ON(mnt->mnt_flags & MNT_UNION);
mnt->mnt_flags = old->mnt_flags;
atomic_inc(&sb->s_active);
mnt->mnt_sb = sb;
@@ -579,16 +583,20 @@ void release_mounts(struct list_head *he
mnt = list_first_entry(head, struct vfsmount, mnt_hash);
list_del_init(&mnt->mnt_hash);
if (mnt->mnt_parent != mnt) {
- struct dentry *dentry;
- struct vfsmount *m;
+ struct path old_nd;
spin_lock(&vfsmount_lock);
- dentry = mnt->mnt_mountpoint;
- m = mnt->mnt_parent;
+ old_nd.dentry = mnt->mnt_mountpoint;
+ old_nd.mnt = mnt->mnt_parent;
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
+ detach_mnt_union(mnt, &old_nd);
spin_unlock(&vfsmount_lock);
- dput(dentry);
- mntput(m);
+ if (mnt->mnt_flags & MNT_UNION) {
+ UM_DEBUG("shrink the mountpoint's dcache\n");
+ shrink_dcache_sb(old_nd.dentry->d_sb);
+ }
+ __dput(old_nd.dentry);
+ mntput(old_nd.mnt);
}
mntput(mnt);
}
@@ -621,6 +629,9 @@ static int do_umount(struct vfsmount *mn
struct super_block *sb = mnt->mnt_sb;
int retval;
LIST_HEAD(umount_list);
+#ifdef CONFIG_UNION_MOUNT
+ struct union_info *uinfo = NULL;
+#endif
retval = security_sb_umount(mnt, flags);
if (retval)
@@ -685,6 +696,14 @@ static int do_umount(struct vfsmount *mn
}
down_write(&namespace_sem);
+#ifdef CONFIG_UNION_MOUNT
+ /*
+* Grab a reference to the union_info which gets detached
+* from the dentries in release_mounts().
+*/
+ if (mnt->mnt_flags & MNT_UNION)
+ uinfo = union_lock_and_get(mnt->mnt_root);
+#endif
spin_lock(&vfsmount_lock);
event++;
@@ -699,6 +718,15 @@ static int do_umount(struct vfsmount *mn
security_sb_umount_busy(mnt);
up_write(&namespace_sem);
release_mounts(&umount_list);
+#ifdef CONFIG_UNION_MOUNT
+ if (uinfo) {
+ if (atomic_read(&uinfo->u_count) == 1)
+ /* We are the last user of this union_info */
+ union_release(uinfo);
+ else
+ union_put_and_unlock(uinfo);
+ }
+#endif
return retval;
}
@@ -941,6 +969,9 @@ static int attach_recursive_mnt(struct v
set_mnt_shared(p);
}
+ if (source_mnt->mnt_flags & MNT_UNION)
+ union_alloc_dentry(nd->dentry);
+
spin_lock(&vfsmount_lock);
if (parent_nd) {
detach_mnt(source_mnt, parent_nd);
@@ -948,6 +979,7 @@ static int attach_recursive_mnt(struct v
touch_mnt_namespace(current->nsproxy->mnt_ns);
} else {
mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
+ attach_mnt_union(source_mnt, nd);
commit_tree(source_mnt);
}
@@ -956,6 +988,7 @@ static int attach_recursive_mnt(struct v
commit_tree(child);
}
spin_unlock(&vfsmount_lock);
+ union_unlock(nd->dentry);
return 0;
}
@@ -1003,6 +1036,12 @@ static int do_change_type(struct nameida
if (nd->dentry != nd->mnt->mnt_root)
return -EINVAL;
+ /*
+* Don't change the type of union mounts
+*/
+ if (nd->mnt->mnt_flags & MNT
