linux-kernel - Re: [PATCH] bpf: use FS_USERNS

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Message-ID: <CAJqdLrpOGmCC2TpUGisBYQCHpjd6L+LQ40UiuNqWS3pOHFkcFQ@mail.gmail.com>
Date: Thu, 5 Feb 2026 18:17:49 +0100
From: Alexander Mikhalitsyn <alexander@...alicyn.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: bot+bpf-ci@...nel.org, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Jeff Layton <jlayton@...nel.org>, 
	Christian Brauner <brauner@...nel.org>, bpf <bpf@...r.kernel.org>, 
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	aleksandr.mikhalitsyn@...urfusion.io, 
	Martin KaFai Lau <martin.lau@...nel.org>, Chris Mason <clm@...a.com>, 
	Ihor Solodrai <ihor.solodrai@...ux.dev>
Subject: Re: [PATCH] bpf: use FS_USERNS_DELEGATABLE for bpffs

Am Do., 5. Feb. 2026 um 17:43 Uhr schrieb Alexei Starovoitov
<alexei.starovoitov@...il.com>:
>
> On Thu, Feb 5, 2026 at 3:27 AM Alexander Mikhalitsyn
> <alexander@...alicyn.com> wrote:
> >
> > Am Do., 5. Feb. 2026 um 12:20 Uhr schrieb <bot+bpf-ci@...nel.org>:
> > >
> > > > diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
> > > > index 005ea3a2c..c350857b2 100644
> > >
> > > [ ... ]
> > >
> > > > @@ -1077,7 +1073,7 @@ static struct file_system_type bpf_fs_type = {
> > > >       .init_fs_context = bpf_init_fs_context,
> > > >       .parameters     = bpf_fs_parameters,
> > > >       .kill_sb        = bpf_kill_super,
> > > > -     .fs_flags       = FS_USERNS_MOUNT,
> > > > +     .fs_flags       = FS_USERNS_DELEGATABLE,
> > > >  };
> > >
> > > FS_USERNS_DELEGATABLE does not appear to be defined anywhere in the kernel
> > > tree. A search of include/linux/fs.h shows only FS_USERNS_MOUNT is defined
> > > (at line 2268), not FS_USERNS_DELEGATABLE.
> > >
> > > The commit message states this flag was "recently introduced", but it is not
> > > present in this codebase. Will this cause a build failure due to an undefined
> > > identifier?
> >
> > Yeah, this should be applied on top of
> > https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/?h=vfs-7.0.misc&id=269c46e936f3b5f2b6b567ca124d5f5ea07a371c
> > in vfs/vfs-7.0.misc I think.

Hi Alexei,

>
> I think it's better to go via bpf-next this after the merge window
> to make sure it goes through full CI run with AI review, etc.

Yeah, thanks to Daniel's suggestion it went through full CI already.
Please, see https://github.com/kernel-patches/bpf/pull/10970#issue-3901410145

Kind regards,
Alex