netdev - Re: [PATCH net-next v2 3/3] genetlink: fit NLMSG

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Message-ID: <20240319104046.203df045@kernel.org>
Date: Tue, 19 Mar 2024 10:40:46 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Stefano Brivio <sbrivio@...hat.com>, davem@...emloft.net,
 netdev@...r.kernel.org, pabeni@...hat.com, jiri@...nulli.us,
 idosch@...sch.org, johannes@...solutions.net, fw@...len.de,
 pablo@...filter.org, Martin Pitt <mpitt@...hat.com>, Paul Holzinger
 <pholzing@...hat.com>, David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH net-next v2 3/3] genetlink: fit NLMSG_DONE into same
 read() as families

On Tue, 19 Mar 2024 18:17:47 +0100 Eric Dumazet wrote:
> > Hi Stefano! I was worried this may happen :( I think we should revert
> > offending commits, but I'd like to take it on case by case basis.
> > I'd imagine majority of netlink is only exercised by iproute2 and
> > libmnl-based tools. Does passt hang specifically on genetlink family
> > dump? Your commit also mentions RTM_GETROUTE. This is not the only
> > commit which removed DONE:
> >
> > $ git log --since='1 month ago' --grep=NLMSG_DONE --no-merges  --oneline
> >
> > 9cc4cc329d30 ipv6: use xa_array iterator to implement inet6_dump_addr()
> > 87d381973e49 genetlink: fit NLMSG_DONE into same read() as families
> > 4ce5dc9316de inet: switch inet_dump_fib() to RCU protection
> > 6647b338fc5c netlink: fix netlink_diag_dump() return value  
> 
> Lets not bring back more RTNL locking please for the handlers that
> still require it.

Definitely. My git log copy/paste is pretty inaccurate, these two are
better examples:

5d9b7cb383bb nexthop: Simplify dump error handling
02e24903e5a4 netlink: let core handle error cases in dump operations

I was trying to point out that we merged a handful of DONE "coalescing"
patches, and if we need to revert - let's only do that for the exact
commands needed. The comment was raised on my genetlink patch while
the discussion in the link points to RTM_GETROUTE.

> The core can generate an NLMSG_DONE by itself, if we decide this needs
> to be done.

Exactly.