Re: [PATCH v4 0/3] fs: allow statmount to fetch the fs_subtype and sb_source

[Ian Kent <raven@themaw.net>]

On 13/11/24 23:18, Jan Kara wrote:
> On Wed 13-11-24 08:45:06, Jeff Layton wrote:
>> On Wed, 2024-11-13 at 12:27 +0100, Karel Zak wrote:
>>> On Tue, Nov 12, 2024 at 02:39:21PM GMT, Christian Brauner wrote:
>>> Next on the wish list is a notification (a file descriptor that can be
>>> used in epoll) that returns a 64-bit ID when there is a change in the
>>> mount node. This will enable us to enhance systemd so that it does not
>>> have to read the entire mount table after every change.
>>>
>> New fanotify events for mount table changes, perhaps?
> Now that I'm looking at it I'm not sure fanotify is a great fit for this
> usecase. A lot of fanotify functionality does not really work for virtual
> filesystems such as proc and hence we generally try to discourage use of
> fanotify for them. So just supporting one type of event (like FAN_MODIFY)
> on one file inside proc looks as rather inconsistent interface. But I
> vaguely remember we were discussing some kind of mount event, weren't we?
> Or was that for something else?

Well, yes, the idea was to be able to avoid the overhead of scanning the

proc mount table(s) pretty much entirely, particularly bad for rapid fire

event handling such as a largish number of rapid mounta or umounts.


Ian