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SubjectRe: [PATCH v7 1/5] lightnvm: Support for Open-Channel SSDs
>> +
>> + /* register with device with a supported BM */
>> + list_for_each_entry(bt, &nvm_bms, list) {
>> + ret = bt->register_bm(dev);
>> + if (ret < 0)
>> + goto err; /* initialization failed */
>> + if (ret > 0) {
>> + dev->bm = bt;
>> + break; /* successfully initialized */
>> + }
>> + }
>
> Why just search it from head to tail? Can user specific it
> in nvm_create_target()?

Hi Yang,

Currently only the rrpc and a couple of out of tree block managers are
built. The register_bm only tries to find a block manager that supports
the device, when it finds it, that one is initialized. It is an open
question on how we choose the right block manager, e.g. a proprietary
and a open-source block manager is in place. Priorities might be a way
to go? or mark certain block managers as a catch all?

Hopefully we will get away with only a single or two block managers in
the future, so we won't have one for each type of device.

>> +
>> + if (!ret) {
>> + pr_info("nvm: no compatible bm was found.\n");
>> + return 0;
>> + }
>
> If we allow nvm_device registered with no bm, we would get
> a NULL pointer reference problem in later using.
>

Yes, definitely. In the care that happens, I envision it should be
possible to register a block manager after a device is loaded, and then
any outstanding devices (which does not have a registered block
manager), will be probed again.

> As mentioned above, why we have to choose bm for nvm in nvm_register?

Without a block manager, we don't know the structure of the device and
how to interact with it. I want to initialize that as soon as possible.
So that layers on top can start interacting.

>
> Thanx
> Yang


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