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[209.85.167.42]) by smtp.gmail.com with ESMTPSA id m8sm10264897lji.12.2020.04.06.09.34.25 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 06 Apr 2020 09:34:26 -0700 (PDT) Received: by mail-lf1-f42.google.com with SMTP id w145so9649lff.3 for ; Mon, 06 Apr 2020 09:34:25 -0700 (PDT) X-Received: by 2002:a19:7706:: with SMTP id s6mr10019987lfc.31.1586190864915; Mon, 06 Apr 2020 09:34:24 -0700 (PDT) MIME-Version: 1.0 References: <2590640.1585757211@warthog.procyon.org.uk> <36e45eae8ad78f7b8889d9d03b8846e78d735d28.camel@themaw.net> <27994c53034c8f769ea063a54169317c3ee62c04.camel@themaw.net> <20200403111144.GB34663@gardel-login> <20200403151223.GB34800@gardel-login> <20200403203024.GB27105@fieldses.org> <20200406091701.q7ctdek2grzryiu3@ws.net.home> In-Reply-To: <20200406091701.q7ctdek2grzryiu3@ws.net.home> From: Linus Torvalds Date: Mon, 6 Apr 2020 09:34:08 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Upcoming: Notifications, FS notifications and fsinfo() To: Karel Zak Cc: "J. Bruce Fields" , Lennart Poettering , Miklos Szeredi , Ian Kent , David Howells , Christian Brauner , Al Viro , dray@redhat.com, Miklos Szeredi , Steven Whitehouse , Jeff Layton , andres@anarazel.de, keyrings@vger.kernel.org, linux-fsdevel , Linux Kernel Mailing List , Aleksa Sarai Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 6, 2020 at 2:17 AM Karel Zak wrote: > > On Fri, Apr 03, 2020 at 04:30:24PM -0400, J. Bruce Fields wrote: > > > > nfs-utils/support/misc/mountpoint.c:check_is_mountpoint() stats the file > > and ".." and returns true if they have different st_dev or the same > > st_ino. Comparing mount ids sounds better. > > BTW, this traditional st_dev+st_ino way is not reliable for bind mounts. > For mountpoint(1) we search the directory in /proc/self/mountinfo. These days you should probably use openat2() with RESOLVE_NO_XDEV. No need for any mountinfo or anything like that. Just look up the pathname and say "don't cross mount-points", and you'll get an error if it's a mount crossing lookup. So this kind of thing is _not_ an argument for another kernel querying interface. We got a new (and better) model for a lot of this. Linus