Re: [PATCH 05/17] nvme: wire-up support for async-passthru on char-device.

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+int nvme_ns_head_chr_async_cmd(struct io_uring_cmd *ioucmd)
+{
+     struct cdev *cdev = file_inode(ioucmd->file)->i_cdev;
+     struct nvme_ns_head *head = container_of(cdev, struct nvme_ns_head, cdev);
+     int srcu_idx = srcu_read_lock(&head->srcu);
+     struct nvme_ns *ns = nvme_find_path(head);
+     int ret = -EWOULDBLOCK;
+
+     if (ns)
+             ret = nvme_ns_async_ioctl(ns, ioucmd);
+     srcu_read_unlock(&head->srcu, srcu_idx);
+     return ret;
+}

No one cares that this has no multipathing capabilities what-so-ever?
despite being issued on the mpath device node?

I know we are not doing multipathing for userspace today, but this
feels like an alternative I/O interface for nvme, seems a bit cripled
with zero multipathing capabilities...

Multipathing is on the radar. Either in the first cut or in
subsequent. Thanks for bringing this up.

Good to know...

So the char-node (/dev/ngX) will be exposed to the host if we enable
controller passthru on the target side. And then the host can send
commands using uring-passthru in the same way.

Not sure I follow...

May I know what are the other requirements here.

Again, not sure I follow... The fundamental capability is to
requeue/failover I/O if there is no I/O capable path available...

Bit of a shame that I missed adding that in the LSF proposal, but it's
correctible.




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