Re: [PATCH v7 1/5] lightnvm: Support for Open-Channel SSDs

From: Dongsheng Yang
Date: Fri Sep 04 2015 - 03:13:05 EST

On 09/02/2015 06:48 PM, Matias BjÃrling wrote:
+ /* 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.

So here is a suggestion, register_bm again
if we found nvm_dev->bm == NULL in create_target(). And if it is still
NULL after that. return an error "nvm: no compatible bm was found"
and stop target creating. Otherwise, there would be a NULL Pointer
reference problem.

That's a real problem I met in my testing and I did this change
in my local using. I hope that's useful to you.

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.


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