Re: [LSF/MM/BPF TOPIC] block drivers in user space

[Bart Van Assche <bvanassche@acm.org>]

On 3/13/22 14:15, Sagi Grimberg wrote:
>
>> We don't want to re-use tcmu's interface.
>>
>> Bodo has been looking into on a new interface to avoid issues tcmu has
>> and to improve performance. If it's allowed to add a tcmu like backend to
>> nvmet then it would be great because lio was not really made with mq and
>> perf in mind so it already starts with issues. I just started doing the
>> basics like removing locks from the main lio IO path but it seems like
>> there is just so much work.
>
> Good to know...
>
> So I hear there is a desire to do this. So I think we should list the
> use-cases for this first because that would lead to different design
> choices.. For example one use-case is just to send read/write/flush
> to userspace, another may want to passthru nvme commands to userspace
> and there may be others...

(resending my reply without truncating the Cc-list)

Hi Sagi,

Haven't these use cases already been mentioned in the email at the start 
of this thread? The use cases I am aware of are implementing 
cloud-specific block storage functionality and also block storage in 
user space for Android. Having to parse NVMe commands and PRP or SGL 
lists would be an unnecessary source of complexity and overhead for 
these use cases. My understanding is that what is needed for these use 
cases is something that is close to the block layer request interface 
(REQ_OP_* + request flags + data buffer).

Thanks,

Bart.