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    From
    SubjectRe: File Descriptors & Linux 2.0
    Date
    Followup to:  <4qs1aq$4qv@picard.cistron.nl>
    By author: miquels@cistron.nl (Miquel van Smoorenburg)
    In newsgroup: linux.dev.kernel
    >
    > I just checked the Linux-2.0.0 kernel and the sys_select function never
    > writes further in your fd_set than the nr_fds argument to select(). This
    > means that if NR_OPEN is increased, and the size of fd_set increases with it,
    > it doesn't have consequences for older applications. The only thing is that
    > an old application can't handle a fd > 255 in a select() if one is passed
    > through fork()/exec() but I know of no applications that do this. So I think
    > you can do this without trouble.
    >
    > If it's the other way around, and you try to pass a nr_fds > NR_OPEN to
    > select() the kernel sys_select function will round it down to NR_OPEN
    > quietly. So that doesn't cause trouble either.
    >
    > Somehow I get the feeling that sys_select() was coded with this already
    > in mind..
    >

    How many applications do you know that actually check if the file
    descriptor they get from the kernel is in the range 0 <= fd < NR_OPEN?
    Most apps just use FD_SET() without any further checking.

    -hpa
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