On Fri, Feb 07, 2014 at 05:40:44PM -0500, J. Bruce Fields wrote:
> On Fri, Feb 07, 2014 at 05:49:06PM +0100, Miklos Szeredi wrote:
> > From: Miklos Szeredi <mszeredi@xxxxxxx>
> >
> > If flags contain RENAME_EXCHANGE then exchange source and destination files.
> > There's no restriction on the type of the files; e.g. a directory can be
> > exchanged with a symlink.
> >
> > Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
> > Reviewed-by: Jan Kara <jack@xxxxxxx>
>
> I don't see any problem with the delegation stuff. Some random
> bikeshedding:
>
> > @@ -2575,6 +2579,10 @@ static void __d_move(struct dentry * dentry, struct dentry * target)
> >
> > /* Unhash the target: dput() will then get rid of it */
>
> I never understood the point of this comment. It's not even right, is
> it? And if anything this makes it less so. Delete?
Not sure, but I think the comment refers to the fact that we can't use
d_delete() for the target, so instead we just unhash it here (which is exactly
what happens for d_delete() if the dentry is still used).
You're right, it makes no sense for the cross-rename case. So adjusted comment
is:
/*
* Unhash the target (d_delete() is not usable here). If exchanging
* the two dentries, then rehash onto the other's hash queue.
*/
>
> > __d_drop(target);
> > + if (exchange) {
> > + __d_rehash(target,
> > + d_hash(dentry->d_parent, dentry->d_name.hash));
> > + }
> >
> > list_del(&dentry->d_u.d_child);
> > list_del(&target->d_u.d_child);
> ...
> > @@ -4042,7 +4057,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
> >
> > old_name = fsnotify_oldname_init(old_dentry->d_name.name);
> > dget(new_dentry);
> > - if (!is_dir)
> > + if (!is_dir || (flags & RENAME_EXCHANGE))
> > lock_two_nondirectories(source, target);
> > else if (target)
> > mutex_lock(&target->i_mutex);
>
> I had to stop to think about that for a minute: OK, so in the normal
> rename case we still need to lock the to-be-deleted target, and
> lock_two_nondirectories won't do that for us because it ignores
> directories. Got it.
>
> This feels a bit ugly but I don't have a better idea.
>
> > @@ -4051,25 +4066,25 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
>
> Most of this function is under (flags & RENAME_EXCHANGE) conditionals at
> this point. Have you looked at how much is duplicated if you split this
> into something like vfs_rename and vfs_exchange?
Split it up and it becomes 106 + 90 lines. Combine it and it's 130 lines. That
comes to 66 common, 64 conditional, doesn't it? So it's half and half.
And I really can't tell which is better in this case.
Thanks,
Miklos
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