linux-ext4 - Re: [PATCH 23/33] generic/{409,410,411,589}: check for stacking mount support

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Message-ID: <CAOQ4uxgQe5thjp_Pfmbwf-P+o9n7a93a7dzS4S0_Rnw--ULBfA@mail.gmail.com>
Date: Thu, 30 Oct 2025 11:25:12 +0100
From: Amir Goldstein <amir73il@...il.com>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: zlang@...hat.com, neal@...pa.dev, fstests@...r.kernel.org, 
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	joannelkoong@...il.com, bernd@...ernd.com
Subject: Re: [PATCH 23/33] generic/{409,410,411,589}: check for stacking mount support

On Wed, Oct 29, 2025 at 2:29 AM Darrick J. Wong <djwong@...nel.org> wrote:
>
> From: Darrick J. Wong <djwong@...nel.org>
>
> _get_mount depends on the ability for commands such as "mount /dev/sda
> /a/second/mountpoint -o per_mount_opts" to succeed when /dev/sda is
> already mounted elsewhere.
>
> The kernel isn't going to notice that /dev/sda is already mounted, so
> the mount(8) call won't do the right thing even if per_mount_opts match
> the existing mount options.
>
> If per_mount_opts doesn't match, we'd have to convey the new per-mount
> options to the kernel.  In theory we could make the fuse2fs argument
> parsing even more complex to support this use case, but for now fuse2fs
> doesn't know how to do that.
>
> Until that happens, let's _notrun these tests.
>
> Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
> ---
>  common/rc         |   24 ++++++++++++++++++++++++
>  tests/generic/409 |    1 +
>  tests/generic/410 |    1 +
>  tests/generic/411 |    1 +
>  tests/generic/589 |    1 +
>  5 files changed, 28 insertions(+)
>
>
> diff --git a/common/rc b/common/rc
> index f5b10a280adec9..b6e76c03a12445 100644
> --- a/common/rc
> +++ b/common/rc
> @@ -364,6 +364,30 @@ _clear_mount_stack()
>         MOUNTED_POINT_STACK=""
>  }
>
> +# Check that this filesystem supports stack mounts
> +_require_mount_stack()
> +{
> +       case "$FSTYP" in
> +       fuse.ext[234])
> +               # _get_mount depends on the ability for commands such as
> +               # "mount /dev/sda /a/second/mountpoint -o per_mount_opts" to
> +               # succeed when /dev/sda is already mounted elsewhere.
> +               #
> +               # The kernel isn't going to notice that /dev/sda is already
> +               # mounted, so the mount(8) call won't do the right thing even
> +               # if per_mount_opts match the existing mount options.
> +               #
> +               # If per_mount_opts doesn't match, we'd have to convey the new
> +               # per-mount options to the kernel.  In theory we could make the
> +               # fuse2fs argument parsing even more complex to support this
> +               # use case, but for now fuse2fs doesn't know how to do that.
> +               _notrun "fuse2fs servers do not support stacking mounts"
> +               ;;

I believe this is true for fuse* in general. no?

Thanks,
Amir.