Re: [PATCH 14/15] nvme: enable FDP support

[Keith Busch <kbusch@kernel.org>]

On Tue, Nov 19, 2024 at 01:16:28PM +0100, Christoph Hellwig wrote:
> +static int nvme_read_fdp_config(struct nvme_ns *ns, struct nvme_ns_info *info)
> +{
> +	struct nvme_fdp_config result;
> +	struct nvme_fdp_config_log *log;
> +	struct nvme_fdp_config_desc *configs;
> +	size_t log_size;
> +	int error;
> +
> +	error = nvme_get_features(ns->ctrl, NVME_FEAT_FDP, info->endgid, NULL,
> +			0, &result);
> +	if (error)
> +		return error;
> +
> +	if (!(result.flags & FDPCFG_FDPE)) {
> +		dev_warn(ns->ctrl->device, "FDP not enable in current config\n");
> +		return -EINVAL;
> +	}
> +
> +	log_size = sizeof(*log) + (result.fdpcidx + 1) * sizeof(*configs);
> +	log = kmalloc(log_size, GFP_KERNEL);
> +	if (!log)
> +		return -ENOMEM;
> +
> +	error = nvme_get_log_lsi(ns->ctrl, info->nsid, NVME_LOG_FDP_CONFIGS,
> +			0, 0, log, log_size, 0, info->endgid);
> +	if (error) {
> +		dev_warn(ns->ctrl->device,
> +			"failed to read FDP config log: 0x%x\n", error);
> +		goto out_free_log;
> +	}
> +
> +	if (le32_to_cpu(log->size) < log_size) {
> +		dev_warn(ns->ctrl->device, "FDP log too small: %d vs %zd\n",
> +				le32_to_cpu(log->size), log_size);
> +		error = -EINVAL;
> +		goto out_free_log;
> +	}
> +
> +	configs = (struct nvme_fdp_config_desc *)(log + 1);
> +	if (le32_to_cpu(configs[result.fdpcidx].nrg) > 1) {
> +		dev_warn(ns->ctrl->device, "FDP NRG > 1 not supported\n");

Why not support multiple reclaim groups?

> +		return -EINVAL;
> +	}

> +	ns->head->runs = le64_to_cpu(configs[result.fdpcidx].runs);

The config descriptors are variable length, so you can't just index into
it. You have to read each index individually to get the next index's offset.
Something like:

	struct nvme_fdp_config_desc *configs;
	void *l;
	int i;

	...

	l = log + 1;
	for (i = 0; i < result.fdpcidx; i++) {
		configs = l;
		l += le16_to_cpu(configs->size);
	}
	ns->head->runs = le64_to_cpu(configs->runs);