Re: [dm-devel] Latest dm-userspace kernel code

[FUJITA Tomonori <fujita tomonori lab ntt co jp>]

Seems that 4th patch is delayed or lost. I'll post it again if it will
not be delivered until tomorrow.

From: Dan Smith <danms us ibm com>
Subject: Re: [dm-devel] Latest dm-userspace kernel code
Date: Fri, 29 Sep 2006 19:39:46 -0700

> FT> - What is the purpose of dmu_request->deps? I guess that it is for
> FT> preventing I/O being reordered. if so, again, you don't need to do
> FT> that.
> 
> Well, the problem is that a block copy would overwrite other requests.
> I think that while a copy is happening, you have to be careful to not
> write into that block so that your writes are not lost.

On second thought, I think that it would be better to handle this in
user space.

If you add a feature to notify I/O completion of user space (I think
this feature is necessary for other reasons too), user-space programs
can take care about this easily. I prefer the dm-userspace kernel
module to just perform I/Os according to requests from user space.