linux-kernel - Re: [RFC PATCH 2/4] Mount changes to support union mount.

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Message-ID: <f5am1v$foi$2@sea.gmane.org>
Date:	Wed, 20 Jun 2007 07:47:11 +0000 (UTC)
From:	Jan Blunck <jblunck@...e.de>
To:	linux-kernel@...r.kernel.org
Cc:	linux-fsdevel@...r.kernel.org
Subject:  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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