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u : unix-porting@lists.apple.com 18 January 2006 • 12:51AM -0500

Re: kqueue and EVFILT_READ on files
by Denis Bredelet

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>>>> He tested /dev/stdin that didn't work either, and a socket that  
>>>> worked.
>>>
>>> That really depends on what type of file stdin was attached to,  
>>> and whether that file type supported read filters (or not).  
>>> Without knowing that, I can't tell you if it should have worked  
>>> or not.  Obviously, it should always work on sockets, whose data  
>>> is known to arrive asynchronously, and therefore read filters are  
>>> meaningful.
>>>
>>> As a general comment, if you hit an EOF, expect the filter to  
>>> become disabled.
>>
>> I found it doesn't seem to work if stdin is attached to the  
>> standard input.
>> Maybe EV_POLL would be some help in that case?
>
> I'm still not parsing this - I know it's stdin, I just don't know  
> what it's connected to.
>
> Specifically, /dev/stdin is an alias for /dev/fd/0, which is an  
> alias for "whatever is open on this processes fd 0".
>
> Doing a stat on the fd should be informative as to what the heck  
> the descriptor is hooked up to.

This is what I gather from fstat:
device=219b1d4  inode=21bc504  uid=503  gid=4  devicetype=4000005  
size=0

I don't know how to interpret this device type, but it is really the  
standard (console) input. I don't know how to define this better.

>
> If it's a regular file, then yes, EV_POLL might be some help.

I couldn't see a difference with or without EV_POLL in the filter-
specific flags.
I asked the customer for sample code. Can I send it to you after  
weeding it out?

Thanks,
-- Denis.

>
> If it's something like a socket or something else, then he'd be  
> better off if he'd just use fd 0, rather than /dev/fd/0 or /dev/
> stdin, since at present it's not possible to reopen sockets via /
> dev/fd0 or /dev/stdin (he's checking the open to see if it fails,  
> right?).
>
> Like I said before, it really depends on the type of file stdin is  
> attached to.
>
> -- Terry

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