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Subject[patch] vsyscall feature

On Tue, 22 Feb 2000, Dean Gaudet wrote:

> out of curiosity, has the fast syscall and fast gettimeofday stuff
> with the nifty kernel-supplied code page made it into the
> kernel/glibc/etc?

nope, 2.5 stuff. You can check out the 2.3.32 patch (which has a working
purely-user-space times() syscall) at:

http://www.redhat.com/~mingo/vsyscall-2.3.32-F4

Documentation/syscall.txt has the design:

+
+ 'x86 Virtual System Call Interface', Ingo Molnar <mingo@redhat.com>
+
+ The point is to have an extensible system call interface. The kernel
+ provides a generic entry point, which is a readonly user-visible page
+ range. User-space does not know about the internals of this entry
+ point, it's a simple generic function call.
+

there are several 'trampoline pages' (both data and code) which are
'dual-mapped': kernel-space has a read-write mapping to the data page,
user-space only has a read-only mapping. This is how sys_times() works.

it's in the prototype stage, but pretty promising IMO, will post a
finished patch once the 2.5 is branched off.

-- mingo


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