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Date:   Thu, 20 Jul 2023 23:35:55 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Daniel Golle <daniel@makrotopia.org>
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Subject: Re: [RFC PATCH 6/6] block: implement NVMEM provider
Message-ID: <ZLonS7QXLj2lg4Zg@infradead.org>
References: <cover.1689802933.git.daniel@makrotopia.org>
 <e5b709e15739dc0563e9497a2dbbe63050381db0.1689802933.git.daniel@makrotopia.org>
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> +static int blk_nvmem_reg_read(void *priv, unsigned int from,
> +			      void *val, size_t bytes)
> +{
> +	pgoff_t f_index = from >> PAGE_SHIFT;
> +	struct address_space *mapping;
> +	struct blk_nvmem *bnv = priv;
> +	size_t bytes_left = bytes;
> +	struct folio *folio;
> +	unsigned long offs, to_read;
> +	void *p;

Btw, this function really should be using kern_read on a file
using filp_open instead of poking into block device internals.
That way you can even have a generic file provider that works
on anything that can be read from.