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    SubjectRe: [PATCHv4 5/6] Allow setting O_NONBLOCK flag for new sockets
    Ulrich Drepper wrote:
    > -----BEGIN PGP SIGNED MESSAGE-----
    > 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
    convention):

    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.

    -hpa
    -
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