From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Sutter Subject: Re: [nft PATCH v2 2/2] src: get rid of printf Date: Thu, 21 Sep 2017 18:21:08 +0200 Message-ID: <20170921162108.GY30364@orbyte.nwl.cc> References: <20170903223441.GB12383@salvia> <20170904075558.10129-1-eric@regit.org> <20170904075558.10129-3-eric@regit.org> <20170904204348.GB14434@salvia> <20170904205304.GA14816@salvia> <20170921153745.GX30364@orbyte.nwl.cc> <20170921154309.GD15946@breakpoint.cc> <20170921155112.GA27800@salvia> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Florian Westphal , Eric Leblond , netfilter-devel@vger.kernel.org To: Pablo Neira Ayuso Return-path: Received: from orbyte.nwl.cc ([151.80.46.58]:44350 "EHLO orbyte.nwl.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750790AbdIUQVN (ORCPT ); Thu, 21 Sep 2017 12:21:13 -0400 Content-Disposition: inline In-Reply-To: <20170921155112.GA27800@salvia> Sender: netfilter-devel-owner@vger.kernel.org List-ID: Hi, On Thu, Sep 21, 2017 at 05:51:12PM +0200, Pablo Neira Ayuso wrote: > On Thu, Sep 21, 2017 at 05:43:09PM +0200, Florian Westphal wrote: > > Phil Sutter wrote: > > > With the proposed implementation of nft_print(), this will be > > > problematic: nft_run_cmd_from_buffer() waits for the command to finish > > > before printing all the output at once. This obviously breaks monitor > > > which runs endlessly. > > > > > > Maybe we should reference nft_print via a function pointer in > > > output_ctx? This would allow to configure a different nft_print > > > implementation which flushes the buffer to stdout immediately. > > > > > > What do you think? > > > > I wondered the same thing. > > > > I have following issue: When using new typeof keyword then listing > > a set definition should output something like > > > > set foo { type typeof(meta iifname) } > > > > Because the kernel has no notion of 'meta iifname', we have to > > store this information in the kernel so we can read it back during > > delinearization. > > > > One way to do this would be to store the 'meta iifname' string in the > > sets userdata. > > > > For that, expr_print() would have to be able to print to a buffer > > (or we would need an expr_snprintf or something similar) to extract > > the convert struct *expr back to its original name. > > > > The other solution would be to stash this in the expression > > during parsing but that seems weird as we need to be able to do such > > conversion anyway when printing the ruleset, so we merely need > > to make this accessible outside of plain printf() to stdout. > > Probably the underlying problem is that the monitor code is that not > delinearing, ie. transforming from netlink to abstract syntax tree > (ast) before printing? No, we are talking about different issues (but with a potential common solution): Florian searches for a way to "convert" an expression from it's binary form (a struct expr) into a human readable string (here: "meta iifname"). We have this "converter" already in very limited form, namely expr_print(). Eric's patch changes that function to make use of nft_print(), which effectively allows to define a custom buffer to print into. Florian, did I get this right? Cheers, Phil