Date: Sat, 15 Jun 2019 17:59:40 +0200 From: Marius Strobl <marius@freebsd.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r349055 - head/sys/net Message-ID: <20190615155940.GM6782@alchemy.franken.de> In-Reply-To: <154077cb-14b1-1dbc-cb65-3233045963c0@cs.duke.edu> References: <201906151107.x5FB7f6N039968@repo.freebsd.org> <154077cb-14b1-1dbc-cb65-3233045963c0@cs.duke.edu>
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On Sat, Jun 15, 2019 at 09:08:05AM -0400, Andrew Gallatin wrote: > On 2019-06-15 07:07, Marius Strobl wrote: > > Author: marius > > Date: Sat Jun 15 11:07:41 2019 > > New Revision: 349055 > > > Log: > > - Replace unused and only ever written to members of public iflib(9) > > structs with placeholders (in the latter case, IFLIB_MAX_TX_BYTES > > etc. are also only ever used for these write-only members if at all, > > so both these macros and members can just go). Using these spares > > may render it possible to merge certain iflib(9) fixes to stable/12. > > Otherwise, changes extending struct if_irq or struct if_shared_ctx > > in any way would break KBI as instances of these are allocated by > > the driver front-ends (by contrast, struct if_pkt_info as well as > > struct if_softc_ctx instances are provided by iflib(9) and, thus, > > may grow at least at the end without breaking KBI). > > Given the above, why replace ipi_tcp_sum in if_pkt_info with a spare? > Given that if_pkt_info can grow, I would also expect it to be able to > shrink. So I don't quite see why the spare is needed here. > > I also worry about carrying the other spares around forever. Yes, KBI-wise it should be also safe for instances of structures allocated by iflib(9) to shrink at the end (though shrinking structures usually isn't a concern when MFCing as such parts may just be omitted); changes altering the offsets of members would be a problem regarding KBI. Still, I don't like changing the size of publicly visible structures in stable branches without a real good reason even if such a change doesn't strictly break the KBI. So the plan is to MFC the spares but then to get rid of the ones whose removal doesn't break KBI in head. Marius
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