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nvme: introduce generic per-namespace chardev
Userspace has not been allowed to I/O to device that's failed to
be initialized. This patch introduces generic per-namespace character
device to allow userspace to I/O regardless the block device is there or
not.
The chardev naming convention will similar to the existing blkdev naming,
using a ng prefix instead of nvme, i.e.
- /dev/ngXnY
It also supports multipath which means it will not expose chardev for the
hidden namespace blkdevs (e.g., nvmeXcYnZ). If /dev/ngXnY is created for
a ns_head, then I/O request will be routed to a specific controller
selected by the iopolicy of the subsystem.
Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Signed-off-by: Javier González <javier.gonz@samsung.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Tested-by: Kanchan Joshi <joshi.k@samsung.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>