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SubjectRe: File Descriptors & Linux 2.0
In article <>,
H. Peter Anvin <> wrote:
>By author: David Schwartz <>
>> It used to be that under 1.3.65 through about 1.3.78 you could go
>> up to 1024 fd's per process by chaning NR_OPEN, NR_FILE, FD_SETSIZE, and
>> a few other little things. That doesn't seem to work on 2.0.0.
>"A few other little things" meaning recompiling libc and all your

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..

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