linux-kernel - Re: [fuse-devel] [PATCH 0/8] MUSE: Userspace backed MTD v3

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Message-ID: <3a9c19cf-2c25-a3bf-a200-6d223952797a@studio.unibo.it>
Date:   Tue, 9 Feb 2021 16:10:41 +0100
From:   Luca Risolia <luca.risolia@...dio.unibo.it>
To:     Richard Weinberger <richard@....at>,
        Miklos Szeredi <miklos@...redi.hu>
Cc:     Vignesh Raghavendra <vigneshr@...com>,
        fuse-devel <fuse-devel@...ts.sourceforge.net>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        Ron Minnich <rminnich@...gle.com>, sven@...fation.org
Subject: Re: [fuse-devel] [PATCH 0/8] MUSE: Userspace backed MTD v3

Hi guys,

a bit OT probably: is there any chance for you to also implement mmap() 
for CUSE? That would be much appreciated.

Thanks


On 09/02/21 15:35, Richard Weinberger wrote:
> Miklos,
> 
> ----- Ursprüngliche Mail -----
>>> The core goal of MUSE is having the complexity on the userspace side and
>>> only a small MTD driver in kernelspace.
>>> While playing with different approaches I realized that FUSE offers everything
>>> we need. So MUSE is a little like CUSE except that it does not implement a
>>> bare character device but an MTD.
>>
>> Looks fine.
> 
> I'm glad to hear that!
> 
>> I do wonder if MUSE should go to drivers/mtd/ instead.   Long term
>> goal would be move CUSE to drivers/char and move the transport part of
>> fuse into net/fuse leaving only the actual filesystems (fuse and
>> virtiofs) under fs/.
>>
>> But for now just moving the minimal interface needed for MUSE into a
>> separate header (<net/fuse.h>) would work, I guess.
>>
>> Do you think that would make sense?
> 
> Yes, I'm all for having MUSE in drivers/mtd/.
> 
> I placed MUSE initially in fs/fuse/ because CUSE was already there and muse.c includes
> fuse_i.h. So tried to be as little invasive as possible.
> 
>>>
>>> Notes:
>>> ------
>>>
>>> - OOB support is currently limited. Currently MUSE has no support for processing
>>>    in- and out-band in the same MTD operation. It is good enough to make JFFS2
>>>    happy. This limitation is because FUSE has no support more than one variable
>>>    length buffer in a FUSE request.
>>>    At least I didn’t find a good way to pass more than one buffer to a request.
>>>    Maybe FUSE folks can correct me. :-)
>>
>> If you look at fuse_do_ioctl() it does variable length input and
>> output at the same time.  I guess you need something similar to that.
> 
> I'll dig into this!
> 
> Thanks,
> //richard
> 
>