Re: RFC: checking file systems support UF_HIDDEN, UF_SYSTEM

On Wed, Jul 2, 2025 at 2:05 PM Shawn Webb <shawn.webb@hardenedbsd.org> wrote:
>
> On Wed, Jul 02, 2025 at 02:02:14PM -0700, Rick Macklem wrote:
> > Hi,
> >
> > I am implementing the "hidden" and "system" attributes for
> > NFSv4 using UF_HIDDEN and UF_SYSTEM.
> >
> > In a couple of places in the code, I need to know if a file
> > system supports these flags.
> > I can think of two ways to do this.
> > #1 - Create a new VFCF_HIDSYS flag that is set via VFS_SET()
> >        for file systems that support the UF_HIDDEN and UF_SYSTEM
> >        flags and test for that flag being set.
> > or
> > #2 - Write it this way...
> >       if (strcmp(vp->v_mount->mnt_vfc->vfc_name, "zfs") != 0 ||
> >           strcmp(vp->v_mount->mnt_vfc->vfc_name, "ufs") != 0 ||
> >           strcmp(vp->v_mount->mnt_vfc->vfc_name, "msdosfs") != 0 ||
> >           strcmp(vp->v_mount->mnt_vfc->vfc_name, "tmpfs") != 0)
> >
> > Which do you think is preferable (or do you have another idea)?
>
> I have no skin in the game, but I'm curious if you could tell me more
> about UF_HIDDEN. Can you explain what that is or perhaps link me to
> some documentation for me to read?
I don't know why or when these were added to FreeBSD, but I believe
their origin is in MSDOS long ago. The fat file system had these two flags
that MSDOS used, called "hiiden" and "system".
I believe "hidden" is somewhat similar to POSIX file
names that start with "." and "system" made the file harder to delete.
(But, I hate to admit I even recall anything about MSDOS;-)

If you google "windows system and hidden" you'll get something that
might answer your question, thanks to their AI.

W.r.t. NFSv4, the current interest is from the group that is working
on the Windows NFSv4.1 client.

rick

>
> Thanks,
>
> --
> Shawn Webb
> Cofounder / Security Engineer
> HardenedBSD
>
> Signal Username:  shawn_webb.74
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