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[82.4.199.187]) by smtp.gmail.com with ESMTPSA id w25sm4577450ejy.123.2020.10.25.14.35.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 25 Oct 2020 14:35:11 -0700 (PDT) Sender: =?UTF-8?Q?Edward_Tomasz_Napiera=C5=82a?= Date: Sun, 25 Oct 2020 21:35:09 +0000 From: Edward Tomasz Napierala To: Cy Schubert Cc: Oliver Pinter , "src-committers@freebsd.org" , "svn-src-all@freebsd.org" , "svn-src-head@freebsd.org" Subject: Re: svn commit: r367038 - head/sbin/mount_nullfs Message-ID: <20201025213509.GA1671@brick> Mail-Followup-To: Cy Schubert , Oliver Pinter , "src-committers@freebsd.org" , "svn-src-all@freebsd.org" , "svn-src-head@freebsd.org" References: <202010251409.09PE91aS001781@repo.freebsd.org> <202010251417.09PEH6tE003403@slippy.cwsent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202010251417.09PEH6tE003403@slippy.cwsent.com> X-Rspamd-Queue-Id: 4CKB8M1lVCz4Yr3 X-Spamd-Bar: - Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20161025 header.b=DVK11h9o; dmarc=none; spf=pass (mx1.freebsd.org: domain of etnapierala@gmail.com designates 2a00:1450:4864:20::636 as permitted sender) smtp.mailfrom=etnapierala@gmail.com X-Spamd-Result: default: False [-1.94 / 15.00]; TO_DN_EQ_ADDR_SOME(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; R_SPF_ALLOW(-0.20)[+ip6:2a00:1450:4000::/36]; RCPT_COUNT_FIVE(0.00)[5]; RCVD_COUNT_THREE(0.00)[3]; DKIM_TRACE(0.00)[gmail.com:+]; NEURAL_HAM_SHORT(-0.25)[-0.248]; FORGED_SENDER(0.30)[trasz@freebsd.org,etnapierala@gmail.com]; RECEIVED_SPAMHAUS_PBL(0.00)[82.4.199.187:received]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2a00:1450::/32, country:US]; FROM_NEQ_ENVFROM(0.00)[trasz@freebsd.org,etnapierala@gmail.com]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-0.99)[-0.990]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; FROM_HAS_DN(0.00)[]; NEURAL_HAM_LONG(-1.01)[-1.006]; TAGGED_RCPT(0.00)[]; MIME_GOOD(-0.10)[text/plain]; DMARC_NA(0.00)[freebsd.org]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCVD_IN_DNSWL_NONE(0.00)[2a00:1450:4864:20::636:from]; MID_RHS_NOT_FQDN(0.50)[]; FREEMAIL_CC(0.00)[gmail.com,freebsd.org]; RCVD_TLS_ALL(0.00)[]; MAILMAN_DEST(0.00)[svn-src-all,svn-src-head] X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 25 Oct 2020 21:35:16 -0000 On 1025T0717, Cy Schubert wrote: > In message om> > , Oliver Pinter writes: > > On Sunday, October 25, 2020, Edward Tomasz Napierala > > wrote: > > > > > Author: trasz > > > Date: Sun Oct 25 14:09:00 2020 > > > New Revision: 367038 > > > URL: https://svnweb.freebsd.org/changeset/base/367038 > > > > > > Log: > > > Remove the check that prevents creating "loops" from mount_nullfs(8). > > > > > > > > The simple question is: why? > > I was about to ask that myself. > > The why is usually more important than the how. Two reasons. First, from what I can tell this is an artificial limitation which serves no purpose. I thought it was to prevent some kind of deadlock between vnodes, so I asked kib@, and he mentioned removing that very limitation from the kernel code; thus, it looks to me like a historical leftover. Second, I've stumbled upon this when trying to nullfs-mount '/' on '/compat/ubuntu/bsd/', which would be useful for autochroot functionality, when (or if) it becomes a thing.