Re: [PATCH v2 00/16] fanotify: add pre-content hooks

[Dave Chinner <david@fromorbit.com>]

On Thu, Aug 08, 2024 at 03:27:02PM -0400, Josef Bacik wrote:
> v1: https://lore.kernel.org/linux-fsdevel/cover.1721931241.git.josef@toxicpanda.com/
> 
> v1->v2:
> - reworked the page fault logic based on Jan's suggestion and turned it into a
>   helper.
> - Added 3 patches per-fs where we need to call the fsnotify helper from their
>   ->fault handlers.
> - Disabled readahead in the case that there's a pre-content watch in place.
> - Disabled huge faults when there's a pre-content watch in place (entirely
>   because it's untested, theoretically it should be straightforward to do).
> - Updated the command numbers.
> - Addressed the random spelling/grammer mistakes that Jan pointed out.
> - Addressed the other random nits from Jan.
> 
> --- Original email ---
> 
> Hello,
> 
> These are the patches for the bare bones pre-content fanotify support.  The
> majority of this work is Amir's, my contribution to this has solely been around
> adding the page fault hooks, testing and validating everything.  I'm sending it
> because Amir is traveling a bunch, and I touched it last so I'm going to take
> all the hate and he can take all the credit.

Brave man. :)

> There is a PoC that I've been using to validate this work, you can find the git
> repo here
> 
> https://github.com/josefbacik/remote-fetch
> 
> This consists of 3 different tools.
> 
> 1. populate.  This just creates all the stub files in the directory from the
>    source directory.  Just run ./populate ~/linux ~/hsm-linux and it'll
>    recursively create all of the stub files and directories.
> 2. remote-fetch.  This is the actual PoC, you just point it at the source and
>    destination directory and then you can do whatever.  ./remote-fetch ~/linux
>    ~/hsm-linux.
> 3. mmap-validate.  This was to validate the pagefault thing, this is likely what
>    will be turned into the selftest with remote-fetch.  It creates a file and
>    then you can validate the file matches the right pattern with both normal
>    reads and mmap.  Normally I do something like
> 
>    ./mmap-validate create ~/src/foo
>    ./populate ~/src ~/dst
>    ./rmeote-fetch ~/src ~/dst
>    ./mmap-validate validate ~/dst/foo

This smells like something that should be added to fstests.

FWIW, fstests used to have a whole "fake-hsm" infrastructure
subsystem in it for testing DMAPI events used by HSMs. They were
removed in this commit:

commit 6497ede7ad4e9fc8e5a5a121bd600df896b7d9c6
Author: Darrick J. Wong <djwong@kernel.org>
Date:   Thu Feb 11 13:33:38 2021 -0800

    fstests: remove DMAPI tests

    Upstream XFS has never supported DMAPI, so remove the tests for this
    feature.

    Signed-off-by: Darrick J. Wong <djwong@kernel.org>
    Acked-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Eryu Guan <guaneryu@gmail.com>

See ./dmapi/src/sample_hsm/ for the HSM test code that was removed
in that patchset - it might provide some infrastructure that can be
used to test the fanotify HSM event infrastructure without
reinventing the entire wheel...

-Dave.
-- 
Dave Chinner
david@fromorbit.com