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    SubjectRe: [PATCH 2.6.21-rc4-mm1 4/4] sys_futex64 : allows 64bit futexes
    On Wed, Mar 21, 2007 at 10:54:36AM +0100, wrote:
    > This last patch is an adaptation of the sys_futex64 syscall provided in -rt
    > patch (originally written by Ingo Molnar). It allows the use of 64-bit futex.
    > I have re-worked most of the code to avoid the duplication of the code.
    > It does not provide the functionality for all architectures (only for x64 for now).

    I don't think you should blindly add all operations to sys_futex64 without
    thinking what they really do.
    E.g. FUTEX_{{,UN,TRY}LOCK,CMP_REQUEUE}_PI doesn't really make any sense for 64-bit
    futexes, the format of PI futexes is hardcoded in the kernel and is always
    32-bit, see FUTEX_TID_MASK, FUTEX_WAITERS, FUTEX_OWNER_DIED definitions.
    exit_robust_list/handle_futex_death will handle 32-bit PI futexes anyway.
    Similarly, sys_futex64 shouldn't support the obsolete operations that
    are there solely for compatibility (e.g. FUTEX_REQUEUE or FUTEX_FD).

    When you just -ENOSYS on the PI ops, there is no need to implement

    FUTEX_WAKE_OP is questionable for 64-bit, IMHO it is better to just
    -ENOSYS on it and only if anyone ever finds actual uses for it, add it.

    For 64-bit futexes the only needed operations are actually
    FUTEX_WAIT and perhaps FUTEX_CMP_REQUEUE, so I wonder if it isn't
    better to just add FUTEX_WAIT64 and FUTEX_CMP_REQUEUE64 ops to sys_futex
    instead of adding a new syscall.

    But the FUTEX_{{,UN,TRY}LOCK,CMP_REQUEUE}_PI removal for 64-bit futexes
    is IMHO the most important part of my complain.

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