From owner-freebsd-current  Wed Jan 26  7:18:22 2000
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From: "Yevmenkin, Maksim N, CSCIO" <myevmenkin@att.com>
To: "'Bruce Evans'" <bde@zeta.org.au>
Cc: "'freebsd-current@freebsd.org'" <freebsd-current@FreeBSD.ORG>,
	"'freebsd-hackers@freebsd.org'" <freebsd-hackers@FreeBSD.ORG>
Subject: RE: BPF bug or not?
Date: Wed, 26 Jan 2000 10:17:53 -0500
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Bruce,

[...]

> > I've just found that read from /dev/bpfX never return 
> EAGAIN/EWOULDBLOCK.
> > It means that when you do a non blocking read and there is 
> no data you will
> > always get 0.
> > 
> > Does it suppose work this way?
> 
> I think it is a bug.  Perhaps applications depend on it.
> 
> Untested fix:

[ untested fix removed :) ]

Yes, it works. But it returns EAGAIN for both O_RDONLY|O_NONBLOCK and 
O_RDWR|O_NONBLOCK open modes. In the same time pipe returns 0 for 
O_RDONLY|O_NONBLOCK mode and EAGAIN for O_RDWR|O_NONBLOCK. 

It there any specs for "read" system call? 

I have small problem with blocking read in pthreads under 3.X. Since
blocking read implemented as non-blocking inside pthread (libc_r to be
honest), returning 0 instead of EAGAIN from read confuses libc_r. It 
expects EAGAIN. 

BTW such "blocking" read inside thread gives almost 100% CPU utilization :(

thanks,

emax


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