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    SubjectRe: [PATCH] poll(2) timeout values
    Willy Tarreau wrote:

    >On Thu, Nov 10, 2005 at 05:15:56PM +0000, Alan Cox wrote:
    >>On Iau, 2005-11-10 at 11:31 -0500, Peter Staubach wrote:
    >>>Clearly, the timeout calculations problem can be fixed without changing
    >>>the arguments to the sys_poll() routine. However, it is cleaner to fix
    >>>it this way by ensuring the sizes and types of arguments match.
    >>There really is no need for the kernel API to match the userspace one,
    >>many of our others differ between the syscall interface which is most
    >>definitely 'exported' in one sense and the POSIX interface which is
    >>defined by libc, posix and the LSB etc
    >>No argument about the timeout fix.
    >I posted a different fix here about a month ago (but I sent it 3 times,
    >as it was twice wrong). Andrew was about to merge it in his tree but I
    >have not checked yet. It was different in the sense that it used
    >msecs_to_jiffies() to do the arithmetic in the best possible way depending
    >on the HZ value and the ints size. Most of the time (when 1000 % HZ == 0),
    >it will simplify the operations to a single divide by a constant and
    >correctly check for integer overflows. Eg, with HZ=250, a simple 2 bits
    >right shift will replace a multiply followed by an divide.
    >I'll check whether 2.6.14-mm1 has it, otherwise I can repost it.

    Yes, I remember the conversation. I hadn't seen the final patch included
    anywhere, so I posted this one.

    That said, I think that msecs_to_jiffies() can still suffer from overflows
    if (HZ % MSECS_PER_SEC) != 0 && (MSECS_PER_SEC % HZ) != 0. I'd like to
    see the rest of your patch to see how this was worked around.

    The patch that I posted does not suffer from overflow issues.


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