From: Jon Maloy <jmaloy@redhat.com>
To: Paolo Abeni <pabeni@redhat.com>,
netdev@vger.kernel.org, davem@davemloft.net
Cc: kuba@kernel.org, passt-dev@passt.top, sbrivio@redhat.com,
lvivier@redhat.com, dgibson@redhat.com
Subject: Re: [RFC net-next] tcp: add support for read with offset when using MSG_PEEK
Date: Thu, 18 Jan 2024 17:22:52 -0500 [thread overview]
Message-ID: <595d89f1-15b1-537d-f876-0ac4627db535@redhat.com> (raw)
In-Reply-To: <df3045c3ec7a4b3c417699ff4950d3d977a0a944.camel@redhat.com>
On 2024-01-16 05:49, Paolo Abeni wrote:
> On Thu, 2024-01-11 at 18:00 -0500, jmaloy@redhat.com wrote:
>> From: Jon Maloy <jmaloy@redhat.com>
>>
>> When reading received messages from a socket with MSG_PEEK, we may want
>> to read the contents with an offset, like we can do with pread/preadv()
>> when reading files. Currently, it is not possible to do that.
[...]
>> + err = -EINVAL;
>> + goto out;
>> + }
>> + peek_offset = msg->msg_iter.__iov[0].iov_len;
>> + msg->msg_iter.__iov = &msg->msg_iter.__iov[1];
>> + msg->msg_iter.nr_segs -= 1;
>> + msg->msg_iter.count -= peek_offset;
>> + len -= peek_offset;
>> + *seq += peek_offset;
>> + }
> IMHO this does not look like the correct interface to expose such
> functionality. Doing the same with a different protocol should cause a
> SIGSEG or the like, right?
I would expect doing the same thing with a different protocol to cause
an EFAULT, as it should. But I haven't tried it.
This is a change to TCP only, at least until somebody decides to
implement it elsewhere (why not?)
>
> What about using/implementing SO_PEEK_OFF support instead?
I looked at SO_PEEK_OFF, and it honestly looks both awkward and limited.
We would have to make frequent calls to setsockopt(), something that
would beat much of the purpose of this feature.
I stand by my opinion here.
This feature is simple, non-intrusive, totally backwards compatible and
implies no changes to the API or BPI.
I would love to hear other opinions on this, though.
Regards
/jon
>
> Cheers,
>
> Paolo
>
next prev parent reply other threads:[~2024-01-18 22:22 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-11 23:00 [RFC net-next] tcp: add support for read with offset when using MSG_PEEK jmaloy
2024-01-16 10:49 ` Paolo Abeni
2024-01-18 22:22 ` Jon Maloy [this message]
2024-01-21 22:16 ` Stefano Brivio
2024-01-22 16:22 ` Jon Maloy
-- strict thread matches above, loose matches on Subject: below --
2024-01-11 22:22 jmaloy
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