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

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Message-ID: <CAJqdLroDeo2CFQA_BT_zV+1NC7WGBo_eb5xG1+hna7sOyAF_Pg@mail.gmail.com>
Date: Thu, 5 Feb 2026 13:49:43 +0100
From: Alexander Mikhalitsyn <alexander@...alicyn.com>
To: Daniel Borkmann <daniel@...earbox.net>
Cc: bot+bpf-ci@...nel.org, ast@...nel.org, andrii@...nel.org, 
	martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, jlayton@...nel.org, 
	brauner@...nel.org, bpf@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, aleksandr.mikhalitsyn@...urfusion.io, 
	martin.lau@...nel.org, clm@...a.com, ihor.solodrai@...ux.dev
Subject: Re: [PATCH] bpf: use FS_USERNS_DELEGATABLE for bpffs

Am Do., 5. Feb. 2026 um 13:38 Uhr schrieb Daniel Borkmann
<daniel@...earbox.net>:
>
> Hi Alexander,
>
> On 2/5/26 12:27 PM, Alexander Mikhalitsyn 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 Daniel,

> If this goes via Christian's vfs tree, it would make sense at least to open a
> test PR against https://github.com/kernel-patches/bpf to run this through the
> BPF CI with the vfs branch + your patch on top to make sure the tests don't
> break.

Sure, https://github.com/kernel-patches/bpf/pull/10970#issue-3901410145

Thanks for suggestion ;-)

Kind regards,
Alex

>
> Thanks,
> Daniel