Re: [PATCH 06/38] whiteout: Add vfs_whiteout() and whiteout inode operation

[Ian Kent <raven@themaw.net>]

Couple of comments below.

On Tue, Jun 15, 2010 at 11:39:36AM -0700, Valerie Aurora wrote:
> From: Jan Blunck <jblunck@suse.de>
> 
> Whiteout a given directory entry.  File systems that support whiteouts
> must implement the new ->whiteout() directory inode operation.
> 
> XXX - Only whiteout when there is a matching entry in a lower layer.
> 
> XXX - MS_WHITEOUT only indicates whiteouts, but we also use it for
> fallthrus.  Can we just check root->i_op->whiteout and ->fallthru?  Or
> do we need an MS_FALLTHRU?
> 
> Signed-off-by: Jan Blunck <jblunck@suse.de>
> Signed-off-by: David Woodhouse <dwmw2@infradead.org>
> Signed-off-by: Valerie Aurora <vaurora@redhat.com>
> ---
>  Documentation/filesystems/vfs.txt |   10 +++++-
>  fs/dcache.c                       |    4 ++-
>  fs/namei.c                        |   73 ++++++++++++++++++++++++++++++++++++-
>  include/linux/dcache.h            |    6 +++
>  include/linux/fs.h                |    2 +
>  5 files changed, 92 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
> index 3de2f32..8846b4f 100644
> --- a/Documentation/filesystems/vfs.txt
> +++ b/Documentation/filesystems/vfs.txt
> @@ -308,7 +308,7 @@ struct inode_operations
>  -----------------------
>  
>  This describes how the VFS can manipulate an inode in your
> -filesystem. As of kernel 2.6.22, the following members are defined:
> +filesystem. As of kernel 2.6.33, the following members are defined:
>  
>  struct inode_operations {
>  	int (*create) (struct inode *,struct dentry *,int, struct nameidata *);
> @@ -319,6 +319,7 @@ struct inode_operations {
>  	int (*mkdir) (struct inode *,struct dentry *,int);
>  	int (*rmdir) (struct inode *,struct dentry *);
>  	int (*mknod) (struct inode *,struct dentry *,int,dev_t);
> +	int (*whiteout) (struct inode *, struct dentry *, struct dentry *);
>  	int (*rename) (struct inode *, struct dentry *,
>  			struct inode *, struct dentry *);
>  	int (*readlink) (struct dentry *, char __user *,int);
> @@ -382,6 +383,13 @@ otherwise noted.
>  	will probably need to call d_instantiate() just as you would
>  	in the create() method
>  
> +  whiteout: called by the rmdir(2) and unlink(2) system calls on a
> +        layered file system.  Only required if you want to support
> +        whiteouts.  The first dentry passed in is that for the old
> +        dentry if it exists, and a negative dentry otherwise.  The
> +        second is the dentry for the whiteout itself.  This method
> +        must unlink() or rmdir() the original entry if it exists.
> +
>    rename: called by the rename(2) system call to rename the object to
>  	have the parent and name given by the second inode and dentry.
>  
> diff --git a/fs/dcache.c b/fs/dcache.c
> index f1358e5..265015d 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -992,8 +992,10 @@ EXPORT_SYMBOL(d_alloc_name);
>  /* the caller must hold dcache_lock */
>  static void __d_instantiate(struct dentry *dentry, struct inode *inode)
>  {
> -	if (inode)
> +	if (inode) {
> +		dentry->d_flags &= ~DCACHE_WHITEOUT;
>  		list_add(&dentry->d_alias, &inode->i_dentry);
> +	}
>  	dentry->d_inode = inode;
>  	fsnotify_d_instantiate(dentry, inode);
>  }
> diff --git a/fs/namei.c b/fs/namei.c
> index f731108..2c723e2 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -1356,7 +1356,6 @@ static int may_delete(struct inode *dir,struct dentry *victim,int isdir)
>  	if (!victim->d_inode)
>  		return -ENOENT;
>  
> -	BUG_ON(victim->d_parent->d_inode != dir);
>  	audit_inode_child(victim, dir);
>  
>  	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
> @@ -2168,6 +2167,78 @@ SYSCALL_DEFINE2(mkdir, const char __user *, pathname, int, mode)
>  	return sys_mkdirat(AT_FDCWD, pathname, mode);
>  }
>  
> +/**
> + * vfs_whiteout: create a whiteout for the given directory entry
> + * @dir: parent inode
> + * @dentry: directory entry to whiteout
> + *
> + * Create a whiteout for the given directory entry.  A whiteout
> + * prevents lookup from dropping down to a lower layer of a union
> + * mounted file system.
> + *
> + * There are two important cases: (a) The directory entry to be
> + * whited-out may already exist, in which case it must first be
> + * deleted before we create the whiteout, and (b) no such directory
> + * entry exists and we only have to create the whiteout itself.
> + *
> + * The caller must pass in a dentry for the directory entry to be
> + * whited-out - a positive one if it exists, and a negative if not.
> + * When this function returns, the caller should dput() the old, now
> + * defunct dentry it passed in.  The dentry for the whiteout itself is
> + * created inside this function.
> + */
> +static int vfs_whiteout(struct inode *dir, struct dentry *old_dentry, int isdir)
> +{
> +	int err;
> +	struct inode *old_inode = old_dentry->d_inode;
> +	struct dentry *parent, *whiteout;
> +
> +	BUG_ON(old_dentry->d_parent->d_inode != dir);
> +
> +	if (!dir->i_op || !dir->i_op->whiteout)
> +		return -EOPNOTSUPP;
> +
> +	/*
> +	 * If the old dentry is positive, then we have to delete this
> +	 * entry before we create the whiteout.  The file system
> +	 * ->whiteout() op does the actual delete, but we do all the
> +	 * VFS-level checks and changes here.
> +	 */
> +	if (old_inode) {
> +		mutex_lock(&old_inode->i_mutex);
> +		if (d_mountpoint(old_dentry)) {
> +			mutex_unlock(&old_inode->i_mutex);
> +			return -EBUSY;
> +		}
> +		if (isdir) {
> +			dentry_unhash(old_dentry);
> +			err = security_inode_rmdir(dir, old_dentry);
> +		} else {
> +				err = security_inode_unlink(dir, old_dentry);

One to many tabs.

> +		}
> +	}
> +
> +	parent = dget_parent(old_dentry);
> +	whiteout = d_alloc_name(parent, old_dentry->d_name.name);
> +
> +	if (!err)
> +		err = dir->i_op->whiteout(dir, old_dentry, whiteout);

err may be used unitialized.

> +
> +	if (old_inode) {
> +		mutex_unlock(&old_inode->i_mutex);
> +		if (!err) {
> +			fsnotify_link_count(old_inode);
> +			d_delete(old_dentry);
> +		}
> +		if (isdir)
> +			dput(old_dentry);
> +	}
> +
> +	dput(whiteout);
> +	dput(parent);
> +	return err;
> +}
> +
>  /*
>   * We try to drop the dentry early: we should have
>   * a usage count of 2 if we're the only user of this
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index eebb617..630baef 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -183,6 +183,7 @@ d_iput:		no		no		no       yes
>  #define DCACHE_INOTIFY_PARENT_WATCHED	0x0020 /* Parent inode is watched by inotify */
>  
>  #define DCACHE_COOKIE		0x0040	/* For use by dcookie subsystem */
> +#define DCACHE_WHITEOUT		0x0080	/* This negative dentry is a whiteout */
>  
>  #define DCACHE_FSNOTIFY_PARENT_WATCHED	0x0080 /* Parent inode is watched by some fsnotify listener */

DCACHE_WHITEOUT == DCACHE_FSNOTIFY_PARENT_WATCHED, is that intended?

>  
> @@ -372,6 +373,11 @@ static inline void dont_mount(struct dentry *dentry)
>  	spin_unlock(&dentry->d_lock);
>  }
>  
> +static inline int d_is_whiteout(struct dentry *dentry)
> +{
> +	return (dentry->d_flags & DCACHE_WHITEOUT);
> +}
> +
>  static inline struct dentry *dget_parent(struct dentry *dentry)
>  {
>  	struct dentry *ret;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index d7ef72a..7afdbd4 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -209,6 +209,7 @@ struct inodes_stat_t {
>  #define MS_KERNMOUNT	(1<<22) /* this is a kern_mount call */
>  #define MS_I_VERSION	(1<<23) /* Update inode I_version field */
>  #define MS_STRICTATIME	(1<<24) /* Always perform atime updates */
> +#define MS_WHITEOUT	(1<<25) /* FS supports whiteout filetype */
>  #define MS_ACTIVE	(1<<30)
>  #define MS_NOUSER	(1<<31)
>  
> @@ -1527,6 +1528,7 @@ struct inode_operations {
>  	int (*mkdir) (struct inode *,struct dentry *,int);
>  	int (*rmdir) (struct inode *,struct dentry *);
>  	int (*mknod) (struct inode *,struct dentry *,int,dev_t);
> +	int (*whiteout) (struct inode *, struct dentry *, struct dentry *);
>  	int (*rename) (struct inode *, struct dentry *,
>  			struct inode *, struct dentry *);
>  	int (*readlink) (struct dentry *, char __user *,int);
> -- 
> 1.6.3.3
> 
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