On Mon, 2020-08-03 at 18:42 +0200, Miklos Szeredi wrote:

On Mon, Aug 3, 2020 at 5:50 PM David Howells [off-list ref]
wrote:

quoted

Hi Linus,

Here's a set of patches that adds a system call, fsinfo(), that
allows
information about the VFS, mount topology, superblock and files to
be
retrieved.

The patchset is based on top of the mount notifications patchset so
that
the mount notification mechanism can be hooked to provide event
counters
that can be retrieved with fsinfo(), thereby making it a lot faster
to work
out which mounts have changed.

Note that there was a last minute change requested by Miklós: the
event
counter bits got moved from the mount notification patchset to this
one.
The counters got made atomic_long_t inside the kernel and __u64 in
the
UAPI.  The aggregate changes can be assessed by comparing pre-
change tag,
fsinfo-core-20200724 to the requested pull tag.

Karel Zak has created preliminary patches that add support to
libmount[*]
and Ian Kent has started working on making systemd use these and
mount
notifications[**].

So why are you asking to pull at this stage?

Has anyone done a review of the patchset?

I have been working with the patch set as it has evolved for quite a
while now.

I've been reading the kernel code quite a bit and forwarded questions
and minor changes to David as they arose.

As for a review, not specifically, but while the series implements a
rather large change it's surprisingly straight forward to read.

In the time I have been working with it I haven't noticed any problems
except for those few minor things that I reported to David early on (in
some cases accompanied by simple patches).

And more recently (obviously) I've been working with the mount
notifications changes and, from a readability POV, I find it's the
same as the fsinfo() code.

I think it's obvious that this API needs more work.  The integration
work done by Ian is a good direction, but it's not quite the full
validation and review that a complex new API needs.

Maybe but the system call is fundamental to making notifications useful
and, as I say, after working with it for quite a while I don't fell
there's missing features (that David hasn't added along the way) and
have found it provides what's needed for what I'm doing (for mount
notifications at least).

I'll be posting a github PR for systemd for discussion soon while I
get on with completing the systemd change. Like overflow handling and
meson build system changes to allow building with and without the
util-linux libmount changes.

So, ideally, I'd like to see the series merged, we've been working on
it for quite a considerable time now.

Ian