Re: [PATCH RFC v2 2/4] ovl: specify layers via file descriptors

[Amir Goldstein <amir73il@gmail.com>]

On Fri, Oct 11, 2024 at 11:46 PM Christian Brauner <brauner@kernel.org> wrote:
>

nit: if you can avoid using the exact same title for the cover letter and
a patch that would be nice (gmail client collapses them together).

> Currently overlayfs only allows specifying layers through path names.
> This is inconvenient for users such as systemd that want to assemble an
> overlayfs mount purely based on file descriptors.
>
> This enables user to specify both:
>
>     fsconfig(fd_overlay, FSCONFIG_SET_FD, "upperdir+", NULL, fd_upper);
>     fsconfig(fd_overlay, FSCONFIG_SET_FD, "workdir+",  NULL, fd_work);
>     fsconfig(fd_overlay, FSCONFIG_SET_FD, "lowerdir+", NULL, fd_lower1);
>     fsconfig(fd_overlay, FSCONFIG_SET_FD, "lowerdir+", NULL, fd_lower2);
>
> in addition to:
>
>     fsconfig(fd_overlay, FSCONFIG_SET_STRING, "upperdir+", "/upper",  0);
>     fsconfig(fd_overlay, FSCONFIG_SET_STRING, "workdir+",  "/work",   0);
>     fsconfig(fd_overlay, FSCONFIG_SET_STRING, "lowerdir+", "/lower1", 0);
>     fsconfig(fd_overlay, FSCONFIG_SET_STRING, "lowerdir+", "/lower2", 0);
>

Please add a minimal example with FSCONFIG_SET_FD to overlayfs.rst.
I am not looking for a user manual, just one example to complement the
FSCONFIG_SET_STRING examples.

I don't mind adding config types on a per need basis, but out of curiosity
do you think the need will arise to support FSCONFIG_SET_PATH{,_EMPTY}
in the future? It is going to be any more challenging than just adding
support for
just FSCONFIG_SET_FD?

Again, not asking you to do extra work for a feature that no user asked for.

Other than that, it looks very nice and useful.

Thanks,
Amir.