linux-kernel - Re: [PATCH] af_unix: Allow Unix sockets to raise SIGURG

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Message-ID: <20210129120250.269c366d@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 29 Jan 2021 12:02:50 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Shoaib Rao <rao.shoaib@...cle.com>
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        andy.rudoff@...el.com
Subject: Re: [PATCH] af_unix: Allow Unix sockets to raise SIGURG

On Fri, 29 Jan 2021 11:48:15 -0800 Shoaib Rao wrote:
> >> SO_OOBINLINE does not control the delivery of signal, It controls how
> >> OOB Byte is delivered. It may not be obvious but this change does not
> >> deliver any Byte, just a signal. So, as long as sendmsg flag contains
> >> MSG_OOB, signal will be delivered just like it happens for TCP.  
> > Not as far as I can read this code. If MSG_OOB is set the data from the
> > message used to be discarded, and EOPNOTSUPP returned. Now the data gets
> > queued to the socket, and will be read inline.  
> 
> Data was discarded because the flag was not supported, this patch 
> changes that but does not support any urgent data.

When you say it does not support any urgent data do you mean the
message len must be == 0 because something is checking it, or that 
the code does not support its handling?

I'm perfectly fine with the former, just point me at the check, please.

> OOB data has some semantics that would have to be followed and if we 
> support SO_OOBINLINE we would have to support NOT SO_OOBINLINE.
> 
> One can argue that we add a socket option to allow this OR just do what 
> TCP does.