Linked by Thom Holwerda on Mon 14th Mar 2011 18:59 UTC
Talk, Rumors, X Versus Y And over the weekend, the saga regarding Canonical, GNOME, and KDE has continued. Lots of comments all over the web, some heated, some well-argued, some wholly indifferent. Most interestingly, Jeff Waugh and Dave Neary have elaborated on GNOME's position after the initial blog posts by Shuttleworth and Seigo, providing a more coherent look at GNOME's side of the story.
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RE[6]: F**k this shit!
by oiaohm on Wed 16th Mar 2011 03:38 UTC in reply to "RE[5]: F**k this shit!"
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"A userspace driver frameworks its far more stable.

So all drivers are better off in userspace?

nt_jerkface good question.

Some drivers at moment will perform badly at the moment done userspace. Mostly due to context switches. But if there was enough demand merging of kernel mode linux would become important. That basically fixes those performance issues completely.

There are a small number like memory management cpu initialization, video card first initialization that simple cannot be done as userspace basically the ones that a base kernel image of linux will not run without. Yes they are still drivers even that they are in the single file kernel blob.

All the module loadable drivers other than a very small percentage(The ones that have todo operations from ring 0 like virtualisation ie ring 0 is not on offer to user-space for very good reasons) would be in most cases be better off done using the userspace api's.

In fact some drivers in the Linux kernel are being tagged to be ported to the userspace api simply to get rid of them out of kernel space.

Most important thing about being done off the userspace api is that if you are having kernel crashes and you suspect a driver if they are are done in the userspace api you could basically switch to a microkernel model. Run the driver in userspace. Application or driver crashing in userspace normally does not equal complete system stop so making it a little simpler to find that one suspect driver.

So why are they not. fuse cuse and buse are the last 8 years. So drivers prior to that were done in kernel space because there really was no other way that would work.

Next is kernel space does have some advantages. Those advantages do explain why the API in there is unstable.

Main reason for using the kernel space over userspace is speed. For the speed there is a price Kernel space driver can bring the system to a grinding halt with a minor error. No such thing as a free lunch.

Due to the fact that kernel space is for speed. Any design error has to be removable at any time. So the API in kernel space are in flux. BKL was a classic example. Good idea a the time. Many years latter it had to go. Stable Kernel ABI based on internal kernel structs would have prevented that removal as fast as it was. Why you are using Kernel mode explains why Linux kernel mode is in flux.

So the deal you choose between with user-space and kernel mode basically is.

Userspace highly stable, issueless with future versions of kernel, unless something really rare happens never crashes you computer(ie driver might get restarted) but slightly slower depending on the device this may even be undetectable, can be cross platform and cross arch at basically the same speed.

Kernel Space. Fast, Can crash your computer with even the smallest error, Will have issues with future versions of kernel at some point due to ABI/API/Locking changes, normally not cross arch or cross platform if cross arch or cross platform normally as slow as the userspace api used from kernel mode or worse slower than using the userspace interfaces in the first place(what is the point).

Note those deals apply to Windows Linux and Solaris to different amounts. Linux with its faster kernel major version cycles shows up will have issues with future versions of kernel more often. Lot of people remember getting Windows 7 and XP before it and finding a stack of devices no longer worked safely ie add the driver upset computer.

Due the risks in kernel space is why Linux people want the source code in there so it can be fully audited. Basically do you like the Blue/Red screen of death or Linux kernel panic. If no you really should agree with what the Linux developers want. Even MS is giving up on the idea. Most of the gains of kernel space are not with the loss in stability.

The way I put is that closed source driver makers wanting to use kernel space are like carrying possible drug using gear into an airport and trying to refuse having you ass and other private areas inspected. Basically inspection should be expected.

Do I expect driver makers or any poor person who has to be inspected at a airport to be happy about it. No I don't that would be asking too much. But they should be understanding why they got what they did.

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