linux-kernel - Re: [PATCH v2] ubi: gluebi: Fix NULL pointer dereference caused by ftl notifier

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Date: Mon, 17 Jun 2024 18:52:40 +0200 (CEST)
From: Richard Weinberger <richard@....at>
To: Gagan Sidhu <broly@....com>
Cc: ZhaoLong Wang <wangzhaolong1@...wei.com>, 
	chengzhihao1 <chengzhihao1@...wei.com>, 
	dpervushin <dpervushin@...eddedalley.com>, 
	linux-kernel <linux-kernel@...r.kernel.org>, 
	linux-mtd <linux-mtd@...ts.infradead.org>, 
	Miquel Raynal <miquel.raynal@...tlin.com>, 
	Vignesh Raghavendra <vigneshr@...com>, 
	yangerkun <yangerkun@...wei.com>, yi zhang <yi.zhang@...wei.com>
Subject: Re: [PATCH v2] ubi: gluebi: Fix NULL pointer dereference caused by
 ftl notifier

----- Ursprüngliche Mail -----
> Von: "Gagan Sidhu" <broly@....com>
> i don’t think my articulation is correct if you interpreted it as that.
> 
> as i understand it, gluebi simply makes it handy when you have a filesystem
> packed within a ubi file, and it will take that file and mount itas a block
> device.

There is no such thing as an UBI file. UBI hosts volumes.
You can install into these volumes whatever you want.
Also a file system such as UBIFS, but this seems not to be the case here.

> so i would say it’s not MTD->UBI->GLUEBI->MTD->MTDBLOCK
> 
> it’d say it’s more MTD->GLUEBI->MTDBLOCK

No. GLUBI emulates a MTD on top of an UBI volume.
So every read/write operation of the filesystem will first to through:

1. block layer
2. MTDBLOCK (and mtd)
3. GLUBI
4. UBI
5. MTD (this time the real one)

Is this really a setup OpenWRT is using?
I'm not saying it's impossible, but far from ideal.
We have UBIBlock for reasons.

Anyway, since the kernel has to be user space friendly and
users seems to use such "odd" stackings I consider reverting this patch.
ZhaoLong Wang, what do you think?

Thanks,
//richard