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

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Date: Mon, 17 Jun 2024 10:05:13 -0600
From: Gagan Sidhu <broly@....com>
To: Richard Weinberger <richard@....at>
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

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.

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

it’d say it’s more MTD->GLUEBI->MTDBLOCK

that is, the squashfs (actual filesystem) is simply wrapped in a ubi file for gluebi, which will then make it a block device.

i’m not using an actual UBIFS anywhere, aside from sitting underneath the squashfs to handle the mapping from the squash to the nand (to handle bad blocks).

e.g. i have a rootfs in a squashfs file
	-i wrap that squashfs file into a squashfs.ubi
	-i use gluebi to detect this squashfs.ubi file as a block device and mount it

that’s about it.


Thanks,
Gagan

> On Jun 17, 2024, at 10:00 AM, Richard Weinberger <richard@....at> wrote:
> 
> ----- Ursprüngliche Mail -----
>> Von: "Gagan Sidhu" <broly@....com>
>> yes, i have a squashfs inside a ubi volume, and i create ubi block device from
>> it.
>> 
>> i do use config_mtd_ubi_block because the filesystem is squashfs.
>> 
>> so i think it’s affirmative to both questions. gluebi for the block device from
>> the ubi.fs file, then config_mtd_ubi_block to mount this read-only filesystem
>> as a block device.
>> 
>> the end result of both options is a read-only block device that can handle bad
>> blocks on nand devices.
>> 
>> if i was using an M25P80, i wouldn’t even be using ubi.
>> 
>> so CONFIG_MTD_UBI_{GLUEBI,BLOCK} are handy for cases where you need an mtd block
>> device with a read-only file system where the UBI takes care of the
>> idiosyncrasies that make NAND (imo, ofc) inferior to SPI
> 
> Isn't MTD -> UBI -> GLUBI -> MTD -> MTDBLOCK performance wise a nightmare?
> We have UBIBlock for this use case.
> 
> Thanks,
> //richard