From: Dan Smith <danms@xxxxxxxxxx> Subject: Re: dm-userspace (no in-kernel cache version) Date: Wed, 13 Sep 2006 06:39:25 -0700 > FT> I'm not sure how this works. Have you explained the details of > FT> this feature in the earlier thread? > > For example, in our CoW case: > > A write is made to a previously unremapped block. We queue that block > and let userspace make a mapping. Then, we allow the write to happen, > but intercept the completion (endio) and notify userspace that it has > completed. Then, userspace flushes its metadata to disk and notifies > the kernel to allow the endio to complete. Without this, a crash > could result in an inconsistent CoW device. (Note this only needs to > happen on the _initial_ write to a block) I see. Thanks. > FT> I see. I don't think that you need to implement it now (simple > FT> code is always better for mainline inclusion), however, it would > FT> be nice to have dmu_event structure for this. > > Well, it's crucial for our CoW work, so unless Alasdair would prefer > me to leave it out in the initial upstream push, I would like to > include it. It was already implemented and working in my original > version. Of course, no problem if the maintainer agrees on it. I just meant that user-kernel APIs must be ready for the future extensions because you cannot change them easily after inclusion. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
