LinuxQuestions.org
View the Most Wanted LQ Wiki articles.
Go Back   LinuxQuestions.org > Forums > LinuxQuestions.org > Linux - News
User Name
Password
Linux - News This forum is for original Linux News. If you'd like to write content for LQ, feel free to contact us.
All threads in the forum need to be approved before they will appear.

Notices

Reply
 
Search this Thread
Old 10-03-2013, 11:43 AM   #1
jeremy
root
 
Registered: Jun 2000
Distribution: Debian, Red Hat, Slackware, Fedora, Ubuntu
Posts: 10,390

Rep: Reputation: 2626Reputation: 2626Reputation: 2626Reputation: 2626Reputation: 2626Reputation: 2626Reputation: 2626Reputation: 2626Reputation: 2626Reputation: 2626Reputation: 2626
Ex-Red Hat Employee Matthew Garrett Comments On the State of XMir


Quote:
XMir's been delayed from Ubuntu 13.10. The stated reason is that multi-monitor support isn't sufficiently reliable. That's true, but it's far from the only problem that XMir still has:

It's still broken on some single-monitor systems

Some machines have display corruption. There are writes to freed memory. To be fair, some of the behaviour that's been seen has been down to underlying bugs in the Xorg drivers that were never triggered under normal use but are hit by XMir. Others are down to implicit assumptions made in the drivers that XMir happens to violate. The problem is that there doesn't appear to have been enough room in the schedule to deal with these interactions, presumably because nobody accounted for the inevitable "This thing we thought would be easy turns out to be difficult" part of the project.

The input driver bug still isn't really fixed

I've mentioned this bug before. It's now marked "Fix released" which is kind of true but not really. Mir now tells XMir that the VT is changing before the VT is changed, but it doesn't wait for that to complete before switching the VTs. Until XMir is scheduled and runs, it's still receiving input events. In most circumstances that window is small, so there's no real risk of triggering it accidentally.

There's one corner case where it might still cause problems. Simply running isn't enough - XMir has to make progress through its event loop. That'll only happen if the X server is processing its wakeup events, and it's possible to effectively stall that by submitting a sufficiently awkward drawing request to the server. The X server will appear to freeze, and if the user then attempts to work out what's going on by switching to a VT and logging in, those input events will still be going to XMir. It's left as an exercise to the reader to construct ways to take advantage of this.

This can't happen in Xorg because the VT switch is blocked until the input devices have been released. Mir could have done the same, but doesn't because of a conscious design decision - in the Ubuntu Phone world, clients stop doing things when they're told to. Ubuntu Desktop is expected to behave the same way.

This is an unfortunate situation to be in. Ubuntu Desktop was told that they were switching to XMir, but Mir development seems to be driven primarily by the needs of Ubuntu Phone. XMir has to do things that no other Mir client will ever cope with, and unless Mir development takes that into account it's inevitably going to suffer breakage like this. Canonical management needs to resolve this if there's any hope of ever shipping XMir as the default desktop environment.

It's still missing features

XMir doesn't support colour profiles. XRandR properties aren't exposed, so there's no way to control TV output encoding or overscan. There's still no hardware cursor support. Switching to XMir now would reduce functionality without providing any user-visible gain.

It's clear that XMir has turned into a larger project than Canonical had originally anticipated, but that's hardly surprising. There's only one developer with previous X experience working on it full-time, and the announced schedule provided no opportunity to deal with unexpected problems. As if that weren't enough, there's obvious conflict between Ubuntu Desktop and Ubuntu Phone when it comes to developer time and required functionality. The one hardware vendor who's willing to take a public stand has demonstrated that they have no interest in supporting XMir, despite Canonical assuring people that they were already engaging in productive negotiations with GPU manufacturers.
More on Matthew Garrett's Blog...

--jeremy
 
  


Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
LXer: INTERVIEW: Matthew Garrett LXer Syndicated Linux News 0 01-27-2013 11:41 PM
LXer: INTERVIEW: Matthew Garrett LXer Syndicated Linux News 0 01-27-2013 11:21 PM
LXer: Red Hat CEO Matthew Szulik steps down LXer Syndicated Linux News 0 12-31-2007 02:42 AM
LXer: Analyst Comments Sink Red Hat Shares LXer Syndicated Linux News 0 10-14-2006 01:03 AM
LXer: Red Hat chief executive Matthew Szulik LXer Syndicated Linux News 0 06-05-2006 04:21 AM


All times are GMT -5. The time now is 09:09 AM.

Main Menu
My LQ
Write for LQ
LinuxQuestions.org is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
Syndicate
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
identi.ca: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration