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SubjectRe: [PATCHv4 5/6] Allow setting O_NONBLOCK flag for new sockets
Ulrich Drepper wrote:
> Hash: SHA1
> H. Peter Anvin wrote:
>> No.
>> I already said I'm not looking at changing the calling convention for
>> existing syscalls.
> I did not suggest or ask for that at all.
> I was asking you to consider the real implementation details for a new
> syscall mechanism.
> We do not want to abandon the use of syscall/sysenter and go back to int
> (on x86/x86-64). This means that you have to come up with a mechanism
> which hooks into the current syscall/sysenter path while preserving full
> backward compatibility.
> Now it's your turn. How do you do this without additional costs?

- Add sys_new_call to the syscall table
- Create a stub thunk:

asmlinkage long sys_old_call(long parm1, long parm2, long parm3)
return sys_new_call(parm1, parm2, parm3, 0);

We have 2^n examples on this in the kernel already.

Or, if the new syscall requires more than 6 parameters (with the current

asmlinkage long sys_new_call6(long parm1, long parm2, long parm3,
long parm4, long parm5,
long __user *additional)
long xparm[3]; /* 8 parameters, total */

if (copy_from_user(xparm, additional, sizeof xparm)
!= sizeof xparm)
return -EFAULT;

return sys_new_call(parm1, parm2, parm3, parm4, parm5,
xparm[0], xparm[1], xparm[2]);

This is a fixed-size copy from userspace, which obviously cannot be avoided.

The C version isn't optimal, obviously, hence my mentioning the
possibility of doing it in the arch layer.

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