Re: [PATCH v5 4/7] dax: add dax_recovery_write to dax_op and dm target type

[Christoph Hellwig <hch@infradead.org>]

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.