In message <1256152779-10054-13-git-send-email-vaurora@xxxxxxxxxx>, Valerie Aurora writes:
> From: Jan Blunck <jblunck@xxxxxxx>
>
> do_whiteout() allows removal of a directory when it has whiteouts but
> is logically empty.
>
> XXX - This patch abuses readdir() to check if the union directory is
> logically empty - that is, all the entries are whiteouts (or "." or
> ".."). Currently, we have no clean VFS interface to ask the lower
> file system if a directory is empty.
>
> Fixes:
> - Add ->is_directory_empty() op
> - Add is_directory_empty flag to dentry (ugly dcache populate)
> - Ask underlying fs to remove it and look for an error return
> - (your idea here)
Yeah, this is a difficult issue. I think the best way would be to
1. add an OPTIONAL ->is_directory_empty() inode op.
2. have the VFS use some default/generic behavior ala filldir_is_empty()
below if inode->i_op->is_directory_empty is NULL. I assume this behavior
will only need to be checked for file systems that support whiteouts in
the first place.
This'll provide some working behavior for all whiteout-supporting file
systems, but allow anyone who wants to develop a more efficient method to
provide one.
> Signed-off-by: Jan Blunck <jblunck@xxxxxxx>
> Signed-off-by: Valerie Aurora <vaurora@xxxxxxxxxx>
> ---
> fs/namei.c | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 85 insertions(+), 0 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index 5da1635..9a62c75 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -2284,6 +2284,91 @@ int vfs_whiteout(struct inode *dir, struct dentry *dentry, int isdir)
> }
>
> /*
> + * This is abusing readdir to check if a union directory is logically empty.
> + * Al Viro barfed when he saw this, but Val said: "Well, at this point I'm
> + * aiming for working, pretty can come later"
> + */
> +static int filldir_is_empty(void *__buf, const char *name, int namlen,
> + loff_t offset, u64 ino, unsigned int d_type)
> +{
Why not make filldir_is_empty() return a bool? That explains more clearly
the function's return code.
> +static int directory_is_empty(struct dentry *dentry, struct vfsmount *mnt)
> +{
This can also return a bool.
> +static int do_whiteout(struct nameidata *nd, struct path *path, int isdir)
> +{
'isdir' can be bool.
> + struct path safe = { .dentry = dget(nd->path.dentry),
> + .mnt = mntget(nd->path.mnt) };
> + struct dentry *dentry = path->dentry;
> + int err;
You might want to move the initialization of 'struct path safe' down below,
and add a BUG_ON(!nd) before that. I think during the development phases of
UM, it's a good idea to have a few more debugging BUG_ON's.
Erez.
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