Re: [PATCH V2 2/2] nvmet: use xarray for ctrl ns storing

[Christoph Hellwig <hch@lst.de>]

Ok, for the target I can see how this makes sense unlike the host.
Comments below:

> -	u64 host_reads = 0, host_writes = 0;
>  	u64 data_units_read = 0, data_units_written = 0;
> -	struct nvmet_ns *ns;
> +	u64 host_reads = 0, host_writes = 0;
>  	struct nvmet_ctrl *ctrl;
> +	struct nvmet_ns *ns;
> +	unsigned long idx;

Please don't randomly reorder the variable declarations.  Same for
later function.

> diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
> index cea7c3834021..d14edaa22ad5 100644
> --- a/drivers/nvme/target/core.c
> +++ b/drivers/nvme/target/core.c
> @@ -10,6 +10,9 @@
>  #include <linux/pci-p2pdma.h>
>  #include <linux/scatterlist.h>
>  
> +#include "../host/nvme.h"
> +#undef CREATE_TRACE_POINTS

We really shoud not include the host nvme.h in the target code.  What
are you trying to get from it?

>  static unsigned int nvmet_max_nsid(struct nvmet_subsys *subsys)
>  {
> -	struct nvmet_ns *ns;
> +	struct nvmet_ns *cur;
> +	unsigned long idx;
> +	unsigned long nsid;
>  
> -	if (list_empty(&subsys->namespaces))
> +	if (xa_empty(&subsys->namespaces))
>  		return 0;
>  
> -	ns = list_last_entry(&subsys->namespaces, struct nvmet_ns, dev_link);
> -	return ns->nsid;
> +	xa_for_each(&subsys->namespaces, idx, cur)
> +		nsid = cur->nsid;
> +
> +	return nsid;

No need for the xa_empty here.  I also forwarded a question to Matthew
if there is a better way to find the highest index.

>  struct nvmet_ns *nvmet_find_namespace(struct nvmet_ctrl *ctrl, __le32 nsid)
>  {
> +	XA_STATE(xas, &ctrl->subsys->namespaces, le32_to_cpu(nsid));
> +	struct nvmet_ns *ns = NULL;
>  
>  	rcu_read_lock();
> +	do {
> +		ns = xas_load(&xas);
> +		if (xa_is_zero(ns))
> +			ns = NULL;
> +	} while (xas_retry(&xas, ns));
>  	if (ns)
>  		percpu_ref_get(&ns->ref);
>  	rcu_read_unlock();

Why doesn't this use xa_load?

> +	ret = xa_insert(&subsys->namespaces, ns->nsid, ns, GFP_KERNEL);
> +	if (ret) {
> +		switch (ret) {
> +		case -ENOMEM:
> +			pr_err("xa insert memory allocation\n");
> +			goto out_unlock;
> +		case -EBUSY:
> +			pr_err("xa insert entry already present\n");
> +			goto out_unlock;
> +		default:
> +			goto out_unlock;
>  		}
>  	}
> +

I don't think we need the switch statement, just return any error
encountered.

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