Re: [PATCH v4] mtd: super: don't rely on mtdblock device minor

From: Christoph Hellwig <hch@lst.de>
To: Daniel Golle <daniel@makrotopia.org>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>,
	linux-mtd@lists.infradead.org,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Richard Weinberger <richard@nod.at>,
	David Woodhouse <dwmw2@infradead.org>,
	Christoph Hellwig <hch@lst.de>, Jan Kara <jack@suse.cz>,
	Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH v4] mtd: super: don't rely on mtdblock device minor
Date: Tue, 11 May 2021 07:49:55 +0200	[thread overview]
Message-ID: <20210511054955.GA6542@lst.de> (raw)
In-Reply-To: <YJmx3Ru/5oyq6Y1a@makrotopia.org>

On Mon, May 10, 2021 at 11:21:17PM +0100, Daniel Golle wrote:
> For blktrans devices with partitions (ie. part_bits != 0) the
> assumption that the minor number of the mtdblock device matches
> the mtdnum doesn't hold true.
> Properly resolve mtd device from blktrans layer instead.

Why are you changing the legacy lookup method that is clearly deprecated
in favor of the mdt* syntax?

> +
> +	if (MAJOR(bdev->bd_dev) == MTD_BLOCK_MAJOR) {
> +		if (!bdev->bd_disk)
> +			goto error_mtdblock;

bdev->bd_disk can't be NULL.

>  
> +		blktrans_dev = (struct mtd_blktrans_dev *)(bdev->bd_disk->private_data);

Overly long line due to the not actually required cast.

But more importantly you can't just look at the private data of a random
block device that you just opened.  There is absolutely no guarantee that
it actually points to a specific private data.

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