Date: Mon, 29 Jan 2024 15:26:31 +0000 (UTC) From: "Bjoern A. Zeeb" <bzeeb-lists@lists.zabbadoz.net> To: Warner Losh <imp@FreeBSD.org> Cc: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: Re: git: 3be59adbb5a2 - main - vtnet: Adjust for ethernet alignment. Message-ID: <n4s5849r-4q46-3628-qq82-p50q3698172n@yvfgf.mnoonqbm.arg> In-Reply-To: <202401290514.40T5Eb1i061789@gitrepo.freebsd.org> References: <202401290514.40T5Eb1i061789@gitrepo.freebsd.org>
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On Mon, 29 Jan 2024, Warner Losh wrote: > The branch main has been updated by imp: > > URL: https://cgit.FreeBSD.org/src/commit/?id=3be59adbb5a2ae7600d46432d3bc82286e507e95 > > commit 3be59adbb5a2ae7600d46432d3bc82286e507e95 > Author: Warner Losh <imp@FreeBSD.org> > AuthorDate: 2024-01-29 05:08:55 +0000 > Commit: Warner Losh <imp@FreeBSD.org> > CommitDate: 2024-01-29 05:08:55 +0000 > > vtnet: Adjust for ethernet alignment. > > If the header that we add to the packet's size is 0 % 4 and we're > strictly aligning, then we need to adjust where we store the header so > the packet that follows will have it's struct ip header properly > aligned. We do this on allocation (and when we check the length of the > mbufs in the lro_nomrg case). We can't just adjust the clustersz in the > softc, because it's also used to allocate the mbufs and it needs to be > the proper size for that. Since we otherwise use the size of the mbuf > (or sometimes the smaller size of the received packet) to compute how > much we can buffer, this ensures no overflows. The 2 byte adjustment > also does not affect how many packets we can receive in the lro_nomrg > case. Doesn't this still include at least these two un-asserted/un-documented asumptions: (a) mbuf space is large enough to hold 2 extra bytes? Is this always the case? (b) the struct sizes assigned to vtnet_hdr_size are not odd numbers of bytes? Could add comments or CTASSERTs? > PR: 271288 > Sponsored by: Netflix > Reviewed by: bryanv > Differential Revision: https://reviews.freebsd.org/D43224 -- Bjoern A. Zeeb r15:7
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