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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <1842689.1596468469@warthog.procyon.org.uk> <1845353.1596469795@warthog.procyon.org.uk> <20200811135419.GA1263716@miu.piliscsaba.redhat.com> <20200812101405.brquf7xxt2q22dd3@ws.net.home> To: Miklos Szeredi Cc: dhowells@redhat.com, Karel Zak , Linus Torvalds , linux-fsdevel , Al Viro , Jeff Layton , Miklos Szeredi , Nicolas Dichtel , Christian Brauner , Lennart Poettering , Linux API , Ian Kent , LSM , Linux Kernel Mailing List Subject: Re: file metadata via fs API (was: [GIT PULL] Filesystem Information) MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <133507.1597239193.1@warthog.procyon.org.uk> Date: Wed, 12 Aug 2020 14:33:13 +0100 Message-ID: <133508.1597239193@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Miklos Szeredi wrote: > You said yourself, that what's really needed is e.g. consistent > snapshot of a complete mount tree topology. And to get the complete > topology FSINFO_ATTR_MOUNT_TOPOLOGY and FSINFO_ATTR_MOUNT_CHILDREN are > needed for *each* individual mount. That's not entirely true. FSINFO_ATTR_MOUNT_ALL can be used instead of FSINFO_ATTR_MOUNT_CHILDREN if you want to scan an entire subtree in one go. It returns the same record type. The result from ALL/CHILDREN includes sufficient information to build the tree. That only requires the parent ID. All the rest of the information TOPOLOGY exposes is to do with propagation. Now, granted, I didn't include all of the topology info in the records returned by ALL/CHILDREN because I don't expect it to change very often. But you can check the event counter supplied with each record to see if it might have changed - and then call TOPOLOGY on the ones that changed. If it simplifies life, I could add the propagation info into ALL/CHILDREN so that you only need to call ALL to scan everything. It requires larger buffers, however. > Adding a few generic binary interfaces is okay. Adding many > specialized binary interfaces is a PITA. Text interfaces are also a PITA, especially when you may get multiple pieces of information returned in one buffer and especially when you throw in character escaping. Of course, we can do it - and we do do it all over - but that doesn't make it efficient. David