Re: [RFC][PATCH 0/76] vfs: 'views' for filesystems with more than one root
From: Amir Goldstein
Date: Thu Jun 07 2018 - 02:06:20 EST
On Wed, Jun 6, 2018 at 11:42 PM, Mark Fasheh <mfasheh@xxxxxxx> wrote:
> Hi Amir, thanks for the comments!
> Btw, sorry that the name is confusing. I've never been good at picking them.
Didn't say that it was confusing. It might very well be the perfect name...
if I only knew what sort of thing we are trying to name...
> That said, if you have a minute to check out the first patch or two you'll
> see that the patches are basically putting a struct in between the super
> block and the inode.
> One thing I'd like to politely suggest is that anyone now following this
> conversation to please read the at least the first patch. It's an easy read
> and I feel like the conversation overall would be much more clear if
> everyone understood what we're going for. I worry that I didn't do a
> particularly good job explaining the actual code changes.
I did look at the patches. They look simple and clean and they solve A problem.
All I'm saying is that we should look at the set of problems that we know of
before we design an abstraction layer.
> Regarding a layout of the problems, I have a more complete e-mail coming
> soon which should describe in detail the issues I've seen with respect to
> how the kernel is exporting ino/dev pairs (outside of statx). fs_view alone
> is not enough to solve that problem. I'd be happy to CC you on that one if
> you'd like.
>> And what is the SUSE way?
> At SUSE, we carry a version of this patch:
> Essentially a callback which was rejected for various reasons.
Don't see a patch here. Wrong link?
> The fs_view work was intended to replace that patch with an upstream
>> FYI, the Overlayfs file/inode mapping is about to change with many
>> VFS hacks queued for removal, so stay tuned.
> Actually, would you mind giving me a pointer to this work? I'd be very
> interested to see what exactly might be changing.
Mostly, less VFS code is going to be exposed to underlying inode:
>> I have an interest of solving another problem.
>> In VFS operations where only inode is available, I would like to be able to
>> report fsnotify events (e.g. fsnotify_move()) only in directories under a
>> certain subtree root. That could be achieved either by bind mount the subtree
>> root and passing vfsmount into vfs_rename() or by defining an fs_view on the
>> subtree and mounting that fs_view.
> I'm not sure whether fs_view works for this. Taking a quick look at
> fsnotify, the state is already on the inode? If there's a globabl fsnotify
> state that needs to be per subtree than yes we could move that to the
> fs_view and you'd simply deref it from the inode struct.
That was my thinking. I have patches to attach an fsnotify mark
to super block. If fs_view could have a root that is different than
super block's root and if file system can guaranty that objects
cannot be moved outside of fs_view root, then fsnotify mark
could be attached to fs_view.