Messages in this thread |  | | Date | Thu, 15 Feb 2007 12:07:38 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [patch 05/11] syslets: core code |
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On Thu, 15 Feb 2007, Linus Torvalds wrote: > > So I think that a good implementation just does everything up-front, and > doesn't _need_ a user buffer that is live over longer periods, except for > the actual results. Exactly because the whole alloc/teardown is nasty.
Btw, this doesn't necessarily mean "not supporting multiple atoms at all".
I think the batching of async things is potentially a great idea. I think it's quite workable for "open+fstat" kind of things, and I agree that it can solve other things too (the "socket+bind+connect+sendmsg+rcv" kind of complex setup things).
But I suspect that if we just said: - we limit these atom sequences to just linear sequences of max "n" ops - we read them all in in a single go at startup
we actually avoid several nasty issues. Not just the memory allocation issue in user space (now it's perfectly ok to build up a sequence of ops in temporary memory and throw it away once it's been submitted), but also issues like the 32-bit vs 64-bit compatibility stuff (the compat handlers would just convert it when they do the initial copying, and then the actual run-time wouldn't care about user-level pointers having different sizes etc).
Would it make the interface less cool? Yeah. Would it limit it to just a few linked system calls (to avoid memory allocation issues in the kernel)? Yes again. But it would simplify a lot of the interface issues.
It would _also_ allow the "sys_aio_read()" function to build up its *own* set of atoms in kernel space to actually do the read, and there would be no impact of the actual run-time wanting to read stuff from user space. Again - it's actually the same issue as with the compat system call: by making the interfaces do things up-front rather than dynamically, it becomes more static, but also easier to do interface translations. You can translate into any arbitrary internal format _once_, and be done with it.
I dunno.
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