Re: ublk: expose ublk device info in sysfs or support ioctls on ublk-control

[Keith Busch <kbusch@kernel.org>]

On Fri, Feb 07, 2025 at 11:50:33AM -0800, Matthew Broomfield wrote:
> Hi all,
> 
> It would be great if there was a sysfs file which exposed "struct
> ublksrv_ctrl_dev_info" so programs written in languages without
> io_uring libraries (such as python) could easily read this information
> for management, testing, or record keeping. Ideally if possible this
> could be something like "/sys/block/ublkbX/ublk_info". Is this
> possible?
> 
> Alternatively, the "/dev/ublk-control" file could support ioctls which
> mimic the io_uring cmds such as UBLK_CMD_GET_DEV_INFO,
> UBLK_CMD_ADD_DEV, etc. This would be more powerful as the block device
> lifecycle management program could be completely independent of both
> io_uring and the program which handles the block IO. However I'm
> skeptical it's worth it in the long run to create a ioctl -> io_uring
> adapter. (As opposed to languages natively supporting io_uring)

It's really not that difficult to make an equivalent ioctl from an
existing uring_cmd.

I think it would be even easier if the ioctl was exposed on the
/dev/ublkcX device instead of the general purpose ublk-control. This way
you can just use the path of the device you want to query instead of
having to look up its dev_id.