On Tue, Feb 13, 2007 at 03:20:42PM +0100, Ingo Molnar wrote: > +Arguments to the system call are implemented via pointers to arguments. > +This not only increases the flexibility of syslet atoms (multiple syslets > +can share the same variable for example), but is also an optimization: > +copy_uatom() will only fetch syscall parameters up until the point it > +meets the first NULL pointer. 50% of all syscalls have 2 or less > +parameters (and 90% of all syscalls have 4 or less parameters). > + > + [ Note: since the argument array is at the end of the atom, and the > + kernel will not touch any argument beyond the final NULL one, atoms > + might be packed more tightly. (the only special case exception to > + this rule would be SKIP_TO_NEXT_ON_STOP atoms, where the kernel will > + jump a full syslet_uatom number of bytes.) ]
What if you need to increase the number of arguments passed to a system call later? That would be an API change since the size of syslet_uatom would change? Also, what if you have an ABI such that: sys_foo(int fd, long long a) where: arg[0] <= fd arg[1] <= unused arg[2] <= low 32-bits a arg[3] <= high 32-bits a it seems you need to point arg[1] to some valid but dummy variable. How do you propose syslet users know about these kinds of ABI issues (including the endian-ness of 64-bit arguments) ? -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
