From nobody Wed Dec 08 20:22:44 2021 X-Original-To: freebsd-fs@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id BF39218D9980 for ; Wed, 8 Dec 2021 20:22:52 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 4J8TB35nnlz3j8p for ; Wed, 8 Dec 2021 20:22:51 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kib@localhost [127.0.0.1]) by kib.kiev.ua (8.16.1/8.16.1) with ESMTPS id 1B8KMiVK018062 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NO); Wed, 8 Dec 2021 22:22:47 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua 1B8KMiVK018062 Received: (from kostik@localhost) by tom.home (8.16.1/8.16.1/Submit) id 1B8KMi3c018061; Wed, 8 Dec 2021 22:22:44 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Wed, 8 Dec 2021 22:22:44 +0200 From: Konstantin Belousov To: Luoqi Chen Cc: freebsd-fs Subject: Re: nullfs traversing mount points (with working code) Message-ID: References: List-Id: Filesystems List-Archive: https://lists.freebsd.org/archives/freebsd-fs List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-fs@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.5 X-Spam-Checker-Version: SpamAssassin 3.4.5 (2021-03-20) on tom.home X-Rspamd-Queue-Id: 4J8TB35nnlz3j8p X-Spamd-Bar: / Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=gmail.com (policy=none); spf=softfail (mx1.freebsd.org: 2001:470:d5e7:1::1 is neither permitted nor denied by domain of kostikbel@gmail.com) smtp.mailfrom=kostikbel@gmail.com X-Spamd-Result: default: False [-0.96 / 15.00]; RCVD_TLS_ALL(0.00)[]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-0.96)[-0.960]; FROM_HAS_DN(0.00)[]; FREEMAIL_FROM(0.00)[gmail.com]; TAGGED_RCPT(0.00)[]; MIME_GOOD(-0.10)[text/plain]; HAS_XAW(0.00)[]; R_SPF_SOFTFAIL(0.00)[~all]; TO_MATCH_ENVRCPT_SOME(0.00)[]; TO_DN_ALL(0.00)[]; NEURAL_HAM_SHORT(-1.00)[-1.000]; RCPT_COUNT_TWO(0.00)[2]; NEURAL_SPAM_LONG(1.00)[0.998]; FREEMAIL_TO(0.00)[gmail.com]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:6939, ipnet:2001:470::/32, country:US]; RCVD_COUNT_TWO(0.00)[2]; FREEMAIL_ENVFROM(0.00)[gmail.com]; DMARC_POLICY_SOFTFAIL(0.10)[gmail.com : No valid SPF, No valid DKIM,none] X-ThisMailContainsUnwantedMimeParts: N On Mon, Dec 06, 2021 at 10:31:28PM -0800, Luoqi Chen wrote: > Hi, > > Recently I had the need to access nfs automounts (for example /net) from > within jails, I searched everywhere but couldn't find any suitable > solution. It seems we still don't support mount point traversal in nullfs, > even though many people have asked for it. I had no choice so I spent a bit > of time adding the support myself, which worked satisfactorily for my own > purpose. I wonder if anyone's interested in taking the code, polishing it > and eventually checking it in. The patch against 13.0-RELENG is at > https://people.freebsd.org/~luoqi/nullxmnt.diff Let's put a note about wanting this feature aside. It is not just polishing, the code is mostly wrong. From a very quick look, it breaks a lot of VFS expectations from a filesystem. For instance, nullfs inherits some behavior flags from the lower fs, which is no longer true with your patch, like mnt_kern_flags initialization in nullfs_mount(). A look at the update to the null_lookup() indicates that you are busying some filesystem while owning some other vnode lock. I suspect that after this update, null_lookup() might call VOP_LOOKUP() for dotdot on rootvp for some mountpoint. At this point I stopped looking.