linux-ext4 - Re: [RFC[RAP]] fuse: use fs-iomap for better performance so we can containerize ext4

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Message-ID: <CAJfpegs_An=3Ghgz5fyo=A_e--gbG5sS1-cDoOJwhfWBx0DBLg@mail.gmail.com>
Date: Thu, 12 Jun 2025 07:54:12 +0200
From: Miklos Szeredi <miklos@...redi.hu>
To: Amir Goldstein <amir73il@...il.com>
Cc: "Darrick J. Wong" <djwong@...nel.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, John@...ves.net, 
	bernd@...ernd.com, joannelkoong@...il.com, Josef Bacik <josef@...icpanda.com>, 
	linux-ext4 <linux-ext4@...r.kernel.org>, "Theodore Ts'o" <tytso@....edu>
Subject: Re: [RFC[RAP]] fuse: use fs-iomap for better performance so we can
 containerize ext4

On Wed, 11 Jun 2025 at 10:54, Amir Goldstein <amir73il@...il.com> wrote:

> There is already a mount option 'rootmode' for st_mode of root inode
> so I suppose we could add the rootino mount option.
>
> Note that currently fuse_fill_super_common() instantiates the root inode
> before negotiating FUSE_INIT with the server.

I'd prefer not to add more mount options like this.

It would be nice to move away from async FUSE_INIT.  It's one of those
things I wish I'd done differently.

Unfortunately I don't think adding FUSE_INIT_SYNC would be sufficient,
as servers might expect the first request to be always FUSE_INIT and
break if it isn't.   Libfuse seems to be okay, but...

One idea is to add an ioctl that the server would call before
mounting, that explicitly allows FUSE_INIT_SYNC.  It's somewhat ugly,
but I can't think of a better solution.

Thanks,
Miklos