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Re: qemu bsd-user plans

From: Peter Maydell
Subject: Re: qemu bsd-user plans
Date: Fri, 8 Jan 2021 19:56:09 +0000

Adding the people to the CC list who were on the previous discussion thread...

-- PMM

On Fri, 8 Jan 2021 at 19:43, Warner Losh <imp@bsdimp.com> wrote:
> The FreeBSD project has rewritten bsd-user. We've been working on this for 
> quite some time (the earliest commits date from 2013). Maybe a dozen people 
> have worked on this over time, and there's 3 or 4 active developers focused 
> on FreeBSD changes at the moment.
> For a while, we'd merge in upstream changes from qemu. This worked great for 
> us, but left us with a big backlog that was hard to upstream. Each of the 
> updates took some time, so we got a little behind.
> So, a few years ago, I spent several weeks converting the tangled merge mess 
> into a set of linear patches and started moving that forward. This was around 
> the time 4.0 was released. I only managed to get the rebase forward to 3.1 
> release at the time before I hit problems related to poor testing environment 
> making it hard to verify newer versions were still working. Plus, we found a 
> few bugs that took a while to resolve for a number of reasons. Now that they 
> are resolved, we're able to use qemu-bsd-user to build ~30k packages for arm, 
> and ~20k for different types of mips in FreeBSD "ports" system. We now have 
> great confidence that it's working well again.
> Now that those bugs are resolved, I started trying to forward-port the 
> two-year-old base and immediately found myself hitting a number of problems. 
> A big problem was that I was re-doing a lot of work that was due to 
> innoculous changes upstream that I wouldn't have to do if the bsd-user 
> changes were upstream. These changes get in the way of dealing with the more 
> substantial structural changes in qemu that have happened.
> There had been talk of doing a remove and replace update of bsd-user. This 
> talk was before I managed to rebase things as far forward as 3.1 even. This 
> appealed to me because we've accumulated about 150 patches to date, many 
> quite large, and curating them into a set of maybe 400 or 500 changes to 
> match the size and scope of most patches I've seen posted to qemu-devel 
> seemed overwhelming.
> However, it's been another year since that plan was hatched, and it's become 
> clear to me that plan won't end in success. The closest I've been able to get 
> is 3.1 when 4.1 was current (about 6 months behind). It's time for a new plan.
> So, my new plan is to rebase what changes I can to the tip of master and 
> submit those for review. I'll work with the developers on the FreeBSD side to 
> ensure they are included in reviews in addition to the normal qemu-devel 
> list. This will allow us to pare down the deltas between our code and 
> upstream to allow us to make progress. The changes will be held to the 
> standard 'makes things better'. Given how broken bsd-user is today in qemu 
> upstream, at first that will a very easy standard to make.
> The first patch I'll submit will be changing MAINTAINERS to point to me, 
> since I'm acting as the point person in this effort. I'll then re-submit some 
> other changes that I've submitted in the past, but CC the FreeBSD folks that 
> are currently active (they were only CC'd to former developers who lack the 
> time to review).
> But before I get too far down this path, I thought I'd send out what's going 
> on to qemu-devel so I can get feedback and adjust the plan into something 
> that's mutually agreeable so time I put towards this is not wasted.
> So, what do people think of these plans?
> Warner

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