It makes little sense for fsmount() to output the warning message when
mount_too_revealing() is violated to kmsg. Instead, the warning should
be output (with a "VFS" prefix) to the fscontext log. In addition,
include the same log message for mount_too_revealing() when doing a
regular mount for consistency.

With the newest fsopen()-based mount(8) from util-linux, the error
messages now look like

  # mount -t proc proc /tmp
  mount: /tmp: fsmount() failed: VFS: Mount too revealing.
	 dmesg(1) may have more information after failed mount system call.

which could finally result in mount_too_revealing() errors being easier
for users to detect and understand.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
Changes in v2:
- Log before setting retval. [Al Viro]
- v1: <https://lore.kernel.org/r/20250806-errorfc-mount-too-revealing-v1-0-536540f51560@cyphar.com>

---
Aleksa Sarai (2):
      fscontext: add custom-prefix log helpers
      vfs: output mount_too_revealing() errors to fscontext

 fs/namespace.c             |  6 ++++--
 include/linux/fs_context.h | 18 ++++++++++++++----
 2 files changed, 18 insertions(+), 6 deletions(-)
---
base-commit: 66639db858112bf6b0f76677f7517643d586e575
change-id: 20250805-errorfc-mount-too-revealing-5d9f670ba770

Best regards,
-- 
Aleksa Sarai <cyphar@cyphar.com>

On Wed, 06 Aug 2025 16:07:04 +1000, Aleksa Sarai wrote:
> It makes little sense for fsmount() to output the warning message when
> mount_too_revealing() is violated to kmsg. Instead, the warning should
> be output (with a "VFS" prefix) to the fscontext log. In addition,
> include the same log message for mount_too_revealing() when doing a
> regular mount for consistency.
> 
> With the newest fsopen()-based mount(8) from util-linux, the error
> messages now look like
> 
> [...]

Nice, thank you!

---

Applied to the vfs-6.18.mount branch of the vfs/vfs.git tree.
Patches in the vfs-6.18.mount branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.18.mount

[1/2] fscontext: add custom-prefix log helpers
      https://git.kernel.org/vfs/vfs/c/49e998eb0154
[2/2] vfs: output mount_too_revealing() errors to fscontext
      https://git.kernel.org/vfs/vfs/c/3441e1534e67