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SubjectRe: ioctls, etc. (was Re: [PATCH 1/4] sas: add flag for locally attached PHYs)
Douglas Gilbert wrote:
> However, the block layer is used in the context of a
> block device (and in some cases a char device).
> If SAS domain discovery is done from the user space, and
> the root file system is the far side of a SAS expander,
> there are no suitable devices, just the SAS initiator
> (HBA) which currently we cannot address via the block layer.

Invalid example. All of the methods listed -- request_queue, netlink,
chrdev, sysfs, ioctl -- will work just fine when the root filesystem is
on the far side of a SAS expander. These are just methods of
communication, nothing more.

In your example -- userspace discovery required before root filesystem
can be found -- a program running from initrd/initramfs would create an
SMP device node, open it, and then proceed with the discovery and
configuration process, which in turn creates the device nodes necessary
to mount the root filesystem.

A request_queue is just a queue. You are in complete control of who are
the producer(s) of requests, and who are consumer(s).


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