From: Jacek Caban <jacek@codeweavers.com>
Subject: Re: [RFC PATCH 0/5] Reducing prefix size with FUSE OverlayFS
Message-Id: <1b1c15fd-0ddc-3f55-4c08-a8a080684b06@codeweavers.com>
Date: Wed, 1 Apr 2020 23:07:58 +0200
In-Reply-To: <20200330122430.2945061-1-rbernon@codeweavers.com>
References: <20200330122430.2945061-1-rbernon@codeweavers.com>

Hi Rémi,

On 30.03.2020 14:24, Rémi Bernon wrote:
> I have been playing with fuse-overlayfs [1] lately to reduce prefix size
> and speed up wine startup time, and I thought maybe someone else could
> be interested, and I would definitely be interested in some feedback,
> especially if anyone already tried.


This is an interesting experiment, do we really need overlayfs to 
achieve that? We control all access to files, so it seems we could 
implement such copy on write in ntdll. On prefix creation we could 
create only some 'markers' in drive_c that ntdll could recognize and 
lookup builtin files for the actual file to open. When opening for read, 
it would just open the file from Wine installation. When opening for 
write, we would need to create the actual file and potentially copy it. 
I'm sure there are a number of things making it tricky, but it should be 
doable. This would not have any of mentioned prefix update problems and 
would be more portable.


One possibility for those 'markers' is something discussed in context of 
Windows symlinks. It could be a UNIX symlink with a magic target with 
magic prefix in its target.


Thanks,

Jacek