linux-kernel - Re: [PATCH v5 4/7] dax: add dax_recovery_write to dax

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Date:   Wed, 2 Feb 2022 05:34:58 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Jane Chu <jane.chu@...cle.com>
Cc:     david@...morbit.com, djwong@...nel.org, dan.j.williams@...el.com,
        hch@...radead.org, vishal.l.verma@...el.com, dave.jiang@...el.com,
        agk@...hat.com, snitzer@...hat.com, dm-devel@...hat.com,
        ira.weiny@...el.com, willy@...radead.org, vgoyal@...hat.com,
        linux-fsdevel@...r.kernel.org, nvdimm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [PATCH v5 4/7] dax: add dax_recovery_write to dax_op and dm
 target type

On Fri, Jan 28, 2022 at 02:31:47PM -0700, Jane Chu wrote:
> dax_recovery_write() dax op is only required for DAX device that
> export DAXDEV_RECOVERY indicating its capability to recover from
> poisons.
> 
> DM may be nested, if part of the base dax devices forming a DM
> device support dax recovery, the DM device is marked with such
> capability.

I'd fold this into the previous 2 patches as the flag and method
are clearly very tightly coupled.

> +static size_t linear_dax_recovery_write(struct dm_target *ti, pgoff_t pgoff,
> +	void *addr, size_t bytes, struct iov_iter *i)

Function line continuations use two tab indentations or alignment after
the opening brace.

> +{
> +	struct dax_device *dax_dev = linear_dax_pgoff(ti, &pgoff);
> +
> +	if (!dax_recovery_capable(dax_dev))
> +		return (size_t) -EOPNOTSUPP;

Returning a negativ errno through an unsigned argument looks dangerous.

> +	/* recovery_write: optional operation. */

And explanation of what the method is use for might be more useful than
mentioning that is is optional.

> +	size_t (*recovery_write)(struct dax_device *, pgoff_t, void *, size_t,
> +				struct iov_iter *);

Spelling out the arguments tends to help readability, but then again
none of the existing methods does it.