[PATCH 0/2] nvme: Support for fused NVME_IOCTL_SUBMIT_IO

[James Smart]

On 1/5/2021 2:49 PM, klayph at gmail.com wrote:
> From: Clay Mayers <clay.mayers at kioxia.com>
>
> Enables fused compare/write to be issued from user mode.
>
> The first patch allows a pair of pass through requests
> to be linked and submitted as a fused pair to the nvme
> device queue.  The second patch exposes it through an
> nvme ioctl so a cmp/write can be issued from user mode.
>
> There was a question regarding Linux support for this
> functionality in nvme-cli.  With these patches, that
> would be possible.
>
> https://github.com/linux-nvme/nvme-cli/issues/318
>
> Clay Mayers (2):
>    nvme: support fused nvme requests
>    nvme: support fused NVME_IOCTL_SUBMIT_IO
>
>   drivers/nvme/host/core.c | 261 ++++++++++++++++++++++++++++++---------
>   drivers/nvme/host/nvme.h |   2 +
>   drivers/nvme/host/pci.c  |  32 ++++-
>   3 files changed, 234 insertions(+), 61 deletions(-)
>

Hmmm... I don't expect fused support to be simple. There's the whole 
notion of: submitting the two commands such that back-to-back queue_rq() 
calls are made to the transport for the same queue and the back-to-back 
calls (different request contexts) just happen to be the fused commands; 
as well as under error, if queues are frozen, then replayed, the same 
back-to-back calling sequence occurs (and I hope a freeze occuring while 
one sent another not, would recover).

And... the transports better be able to support fused commands as well.  
nvme-fc does not as fused commands were explicitly deemed unsupported.

But - I'll look to see what you have in the patches.

-- james

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