Messages in this thread | | | Date | Sat, 23 Jan 1999 16:32:15 +0100 (CET) | From | MOLNAR Ingo <> | Subject | Re: User vs. Kernel (was: To be smug, or not to be smug, that is , the question) |
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On Sat, 23 Jan 1999, Albert D. Cahalan wrote:
> >> * Lack of generalized message passing > > > > (RT-signals in Linux, a feature of Linux 2.2) > > Could user acahalan send 42 bytes to user mmuscovi?
sure, 'mail mmuscovi < ./42bytefile'. What are you trying to achieve and why?
> >> * Lack of a decent privilege/capability model > > > > (i guess you missed include/linux/capability.h, a feature of 2.2. > > Not completely finished, but the main mechanizm is in there.) > > I believe he means "true" capability support. In any case, > Linux can't revoke normal user capabilities.
what do you mean by 'true'. what is 'user capabilities'. If you mean military grade security, where one can restrict a user to be able only to execute the 'nop' assembly instruction, then you are right, Linux's doesnt want to do that. Linux has a capability model that splits up _system_ priviledges (thus risks) so that eg. a security hole in 'ping' doesnt mean a full system compromise.
> >> * Blocking I/O > > > > (whats your problem with that?) > > This limits concurrency. Within the kernel, IO events need not be > serialized. User-space can only get this ability with threads. > Threads are quite a bit of overhead for such a simple need, plus > the use of threads tends to promote bugs.
take a look at async networking IO, fcntl(SETSIG), etc, implemented by Stephen Tweedie recently. (it's in 2.2)
> >> * Interruptible system calls > > > > (what is your point here) > > It is not good to return to userspace, loop around, and make the system > call a second time. The overhead [...]
Albert, do you have the slightest clue how often it happens to restart a system call, in a typical Linux system? Just for kicks, i've added a small hack to my kernel 5 minutes ago to count them:
total syscalls: 28456 restarted syscalls: 7
what overhead exactly are you complaining about? ...
> [...] and app code complexity are annoying.
the application sees _nothing_ from a system call restart to begin with. It's handled in libc.
-- mingo
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