On Mon, Nov 30, 2009 at 01:13:36AM -0500, Erez Zadok wrote:
> 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.
I hear you, but I'm reluctant to keep a generic version of
is_directory_empty() because, (1) you have to add support for
whiteouts and fallthrus anyway, you might as well require support for
is_directory_empty() op at the same time, (2) per-fs versions would be
undoubtedly more efficient than bouncing up and down through
readdir(), and (3) it's such an abuse. :)
> > 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.
In general, I'm not using bools because it doesn't fit in with the
coding style of the rest of the VFS.
> > + 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.
I'd rather get rid of the need for struct path safe entirely...
-VAL
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
