Re: [Boost-users] [asio] Problem Assignin a File Descriptor to posix:basic_stream_descriptor

Subject: Re: [Boost-users] [asio] Problem Assignin a File Descriptor to posix:basic_stream_descriptor
From: Nader Salehi (Nader.Salehi_at_[hidden])
Date: 2010-03-18 13:22:32

I see.  At this time the path of least resistance would be to use
libevent which allows me --albiet awkwardly via setenv()-- to choose
the polling method.

Thanks for the reply.

Nader

On 3/17/2010 21:19 Nick Jones writes:
> On Wed, 2010-03-17 at 14:42 -0700, Nader Salehi wrote:
> 
> > I traced down the epoll_reactor::register_descriptor() where the
> > function fails to add the descriptor to the poll list.
> > 
> > Any idea what I am doing wrong?  I would appreciate any comment.
> > 
> 
> Filesystem fds do not support epoll, as they lack the poll function
> internally in the linux kernel.  otoh, select does supports filesystem
> fds.
> 
> If you do an strace of your sample program, you will see that the call
> to epoll_ctl fails with the error number EPERM.  Yes, the value chosen
> is quite unfortunate, I always thought it would have been better to
> return ENOTSUP or EOPNOTSUPP... anyhow, that means that epoll is
> rejecting the fd you supplied, in this case because it was a filesystem
> fd and in Linux, this type of fd lacks a poll function pointer in its
> file_operations structure.  I remember looking through the epoll sources
> in an older version of the kernel, and finding that this was the only
> reason that EPERM is returned as an error.
> 
> You may have to find another method of managing IO from and to the file,
> perhaps you can use another standard or asio provided stream type?
> 
> Thanks
> 
>   Nick
> 
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