Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751292Ab0GMEj5 (ORCPT ); Tue, 13 Jul 2010 00:39:57 -0400 Received: from out1.smtp.messagingengine.com ([66.111.4.25]:41332 "EHLO out1.smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751032Ab0GMEjz (ORCPT ); Tue, 13 Jul 2010 00:39:55 -0400 X-Sasl-enc: 30nHG9G0w29eCIX0f3r11proAgKMI+JRT2AqrkZyFTlG 1278995993 Date: Tue, 13 Jul 2010 12:39:46 +0800 From: Ian Kent To: Valerie Aurora Cc: Alexander Viro , Miklos Szeredi , Jan Blunck , Christoph Hellwig , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 19/38] union-mount: Introduce union_dir structure and basic operations Message-ID: <20100713043945.GE3949@zeus.themaw.net> References: <1276627208-17242-1-git-send-email-vaurora@redhat.com> <1276627208-17242-20-git-send-email-vaurora@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1276627208-17242-20-git-send-email-vaurora@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 10442 Lines: 325 On Tue, Jun 15, 2010 at 11:39:49AM -0700, Valerie Aurora wrote: > This patch adds the basic structures and operations of VFS-based union > mounts (but not the ability to mount or lookup unioned file systems). > Each directory in a unioned file system has an associated union stack > created when the directory is first looked up. The union stack is a > union_dir structure kept in a hash table indexed by mount and dentry > of the directory; thus, specific paths are unioned, not dentries > alone. The union_dir keeps a pointer to the upper path and the lower > path and can be looked up by either path. Currently only two layers > are supported, but the union_dir struct is flexible enough to allow > more than two layers. > > This particular version of union mounts is based on ideas by Jan > Blunck, Bharata Rao, and many others. > > Signed-off-by: Valerie Aurora > --- > fs/Kconfig | 13 +++++ > fs/Makefile | 1 + > fs/dcache.c | 3 + > fs/union.c | 119 ++++++++++++++++++++++++++++++++++++++++++++++++ > fs/union.h | 66 ++++++++++++++++++++++++++ > include/linux/dcache.h | 4 +- > include/linux/fs.h | 1 + > 7 files changed, 206 insertions(+), 1 deletions(-) > create mode 100644 fs/union.c > create mode 100644 fs/union.h > > diff --git a/fs/Kconfig b/fs/Kconfig > index 5f85b59..f99c3a9 100644 > --- a/fs/Kconfig > +++ b/fs/Kconfig > @@ -59,6 +59,19 @@ source "fs/notify/Kconfig" > > source "fs/quota/Kconfig" > > +config UNION_MOUNT > + bool "Union mounts (writable overlasy) (EXPERIMENTAL)" Spelling of overlay > + depends on EXPERIMENTAL > + help > + Union mounts allow you to mount a transparent writable > + layer over a read-only file system, for example, an ext3 > + partition on a hard drive over a CD-ROM root file system > + image. > + > + See for details. > + > + If unsure, say N. > + > source "fs/autofs/Kconfig" > source "fs/autofs4/Kconfig" > source "fs/fuse/Kconfig" > diff --git a/fs/Makefile b/fs/Makefile > index 97f340f..1949af2 100644 > --- a/fs/Makefile > +++ b/fs/Makefile > @@ -52,6 +52,7 @@ obj-$(CONFIG_NFS_COMMON) += nfs_common/ > obj-$(CONFIG_GENERIC_ACL) += generic_acl.o > > obj-y += quota/ > +obj-$(CONFIG_UNION_MOUNT) += union.o > > obj-$(CONFIG_PROC_FS) += proc/ > obj-y += partitions/ > diff --git a/fs/dcache.c b/fs/dcache.c > index 1575af4..54ff5a3 100644 > --- a/fs/dcache.c > +++ b/fs/dcache.c > @@ -960,6 +960,9 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name) > INIT_LIST_HEAD(&dentry->d_lru); > INIT_LIST_HEAD(&dentry->d_subdirs); > INIT_LIST_HEAD(&dentry->d_alias); > +#ifdef CONFIG_UNION_MOUNT > + dentry->d_union_dir = NULL; > +#endif > > if (parent) { > dentry->d_parent = dget(parent); > diff --git a/fs/union.c b/fs/union.c > new file mode 100644 > index 0000000..02abb7c > --- /dev/null > +++ b/fs/union.c > @@ -0,0 +1,119 @@ > + /* > + * VFS-based union mounts for Linux > + * > + * Copyright (C) 2004-2007 IBM Corporation, IBM Deutschland Entwicklung GmbH. > + * Copyright (C) 2007-2009 Novell Inc. > + * Copyright (C) 2009-2010 Red Hat, Inc. > + * > + * Author(s): Jan Blunck (j.blunck@tu-harburg.de) > + * Valerie Aurora > + * > + * This program is free software; you can redistribute it and/or > + * modify it under the terms of the GNU General Public License > + * as published by the Free Software Foundation; version 2 > + * of the License. > + */ > + > +#include > +#include > +#include > +#include > +#include > +#include > +#include > + > +#include "union.h" > + > +static struct kmem_cache *union_cache; > + > +static int __init init_union(void) > +{ > + union_cache = KMEM_CACHE(union_dir, SLAB_PANIC | SLAB_MEM_SPREAD); I know there are other places where we just assume KMEM_CACHE() returns non-null but is that really the right thing to do? > + return 0; > +} > + > +fs_initcall(init_union); > + > +/** > + * union_alloc - allocate a union_dir > + * > + * @path: path of directory underneath another directory > + * > + * Allocate a union_dir for this directory. We only allocate > + * union_dirs for the second and lower layers - the read-only layers. > + * Top-level dentries don't have a union_dir, just a pointer to the > + * union_dir of the directory in the layer below it. u_lower is > + * initialized to NULL by default. If there is another layer below > + * this and a matching directory in the layer, then we allocate a > + * union_dir for it and then set u_lower of the above union_dir to > + * point to it. > + */ > + > +static struct union_dir *union_alloc(struct path *path) > +{ > + struct union_dir *ud; > + > + BUG_ON(!S_ISDIR(path->dentry->d_inode->i_mode)); > + > + ud = kmem_cache_alloc(union_cache, GFP_ATOMIC); > + if (!ud) > + return NULL; > + > + ud->u_this = *path; > + ud->u_lower = NULL; > + > + return ud; > +} > + > +static void union_put(struct union_dir *ud) > +{ > + path_put(&ud->u_this); > + kmem_cache_free(union_cache, ud); > +} > + > +/** > + * union_add_dir - Add another layer to a unioned directory > + * > + * @upper - directory in the previous layer > + * @lower - directory in the current layer > + * @next_ud - location of pointer to this union_dir > + * > + * Must have a reference (i.e., call path_get()) to @lower before > + * passing to this function. > + */ > + > +int union_add_dir(struct path *upper, struct path *lower, > + struct union_dir **next_ud) > +{ > + struct union_dir *ud; > + > + BUG_ON(*next_ud != NULL); > + > + ud = union_alloc(lower); > + if (!ud) > + return -ENOMEM; > + *next_ud = ud; > + > + return 0; > +} > + > +/** > + * d_free_unions - free all unions for this dentry > + * > + * @dentry - topmost dentry in the union stack to remove > + * > + * This must be called when freeing a dentry. > + */ > +void d_free_unions(struct dentry *dentry) > +{ > + struct union_dir *this, *next; > + > + this = dentry->d_union_dir; > + > + while (this != NULL) { > + next = this->u_lower; > + union_put(this); > + this = next; > + } > + dentry->d_union_dir = NULL; > +} > diff --git a/fs/union.h b/fs/union.h > new file mode 100644 > index 0000000..04efc1f > --- /dev/null > +++ b/fs/union.h > @@ -0,0 +1,66 @@ > + /* > + * VFS-based union mounts for Linux > + * > + * Copyright (C) 2004-2007 IBM Corporation, IBM Deutschland Entwicklung GmbH. > + * Copyright (C) 2007-2009 Novell Inc. > + * Copyright (C) 2009-2010 Red Hat, Inc. > + * > + * Author(s): Jan Blunck (j.blunck@tu-harburg.de) > + * Valerie Aurora > + * > + * This program is free software; you can redistribute it and/or > + * modify it under the terms of the GNU General Public License > + * as published by the Free Software Foundation; version 2 > + * of the License. > + */ > +#ifndef __LINUX_UNION_H > +#define __LINUX_UNION_H > +#ifdef __KERNEL__ > + > +#ifdef CONFIG_UNION_MOUNT > + > +/* > + * WARNING! Confusing terminology alert. > + * > + * Note that the directions "up" and "down" in union mounts are the > + * opposite of "up" and "down" in normal VFS operation terminology. > + * "up" in the rest of the VFS means "towards the root of the mount > + * tree." If you mount B on top of A, following B "up" will get you > + * A. In union mounts, "up" means "towards the most recently mounted > + * layer of the union stack." If you union mount B on top of A, > + * following A "up" will get you to B. Another way to put it is that > + * "up" in the VFS means going from this mount towards the direction > + * of its mnt->mnt_parent pointer, but "up" in union mounts means > + * going in the opposite direction (until you run out of union > + * layers). > + */ > + > +/* > + * The union_dir structure. Basically just a singly-linked list with > + * a pointer to the referenced dentry, whose head is d_union_dir in > + * the dentry of the topmost directory. We can't link this list > + * purely through list elements in the dentry because lower layer > + * dentries can be part of multiple union stacks. However, the > + * topmost dentry is only part of one union stack. So we point at the > + * lower layer dentries through a linked list rooted in the topmost > + * dentry. > + */ > +struct union_dir { > + struct path u_this; /* this is me */ > + struct union_dir *u_lower; /* this is what I overlay */ > +}; > + > +#define IS_MNT_UNION(mnt) ((mnt)->mnt_flags & MNT_UNION) > + > +extern int union_add_dir(struct path *, struct path *, struct union_dir **); > +extern void d_free_unions(struct dentry *); > + > +#else /* CONFIG_UNION_MOUNT */ > + > +#define IS_MNT_UNION(x) (0) > +#define union_add_dir(x, y, z) ({ BUG(); (NULL); }) > +#define d_free_unions(x) do { } while (0) > + > +#endif /* CONFIG_UNION_MOUNT */ > +#endif /* __KERNEL__ */ > +#endif /* __LINUX_UNION_H */ > diff --git a/include/linux/dcache.h b/include/linux/dcache.h > index 01d6011..509a637 100644 > --- a/include/linux/dcache.h > +++ b/include/linux/dcache.h > @@ -100,7 +100,9 @@ struct dentry { > struct hlist_node d_hash; /* lookup hash list */ > struct dentry *d_parent; /* parent directory */ > struct qstr d_name; > - > +#ifdef CONFIG_UNION_MOUNT > + struct union_dir *d_union_dir; /* head of union stack */ > +#endif > struct list_head d_lru; /* LRU list */ > /* > * d_child and d_rcu can share memory > diff --git a/include/linux/fs.h b/include/linux/fs.h > index dbd9881..32e6988 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -1395,6 +1395,7 @@ struct super_block { > * read-only. > */ > int s_hard_readonly_users; > + Extra blank line, intended? > }; > > extern struct timespec current_fs_time(struct super_block *sb); > -- > 1.6.3.3 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/