Messages in this thread | | | From | "Henrik Rydberg" <> | Date | Mon, 27 Feb 2012 01:01:29 +0100 | Subject | Re: Can we move device drivers into user-space? |
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Hi David,
> the point that you seem to be missing is that the interfaces between > the different areas of the kernel are not stable, they change over > time.
The argument was based on the idea that they would stabilize over time. However, I realize this may not be true, which was also touched upon in a later reply. The heavy-tailed nature of large changes in open-source projects seems to put some hard numbers behind that claim [1].
> When both sides of the interface are in the kernel, this is > not a problem, both sides get changed, but if one side was out of > the kernel, then you either can't make the change, or have a flag > day change where both sides need to change in lock-step (and > downgrading is hard as both sides need to change again)
Assuming the interfaces changes, this follows naturally, of course.
> This is completely ignoring the performance and security aspects of > userspace components vs kernel components.
Indeed.
> Ted is explaining the performance aspects well, but let's look at > the security aspects as well. > > It's not just a case of "if something in userspace crashes, it > doesn't crash the kerenl", it's also a case that "if you have a > userspace component, then the kernel must sanity check the userspace > interface to defend against rogue userspace". Doing these checks is > not cheap (adding to performance overhead), and may not even be > possible (how do you know if the command being sent to the SCSI bus > is safe or not?)
No doubt, an open-ended system has its own set of problems. At any given system size, the question is how this balances against a closed system. The assumption I made was that as the system grows, the balance would shift in favor of an open-ended system. This may not be the case at all, as you are saying. It would be nice to be able to see this in a quantitative manner if possible.
Thanks for taking the time to respond.
Henrik
[1] http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.91.7114
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