Re: [PATCH v5 3/3] landlock.7: Explain the best-effort fallback mechanism in the example

["Günther Noack" <gnoack3000@gmail.com>]

Hello!

On Sun, Apr 02, 2023 at 12:01:43AM +0200, Alejandro Colomar wrote:
> On 4/1/23 19:19, Günther Noack wrote:
> > (It feels out of scope for this documentation patch, but do you think
> > these bitmasks should be defined in the uapi/linux/landlock.h header?
> > You have looked at so many man pages already -- Do you happen to know
> > other places in the kernel API where such a problem has come up?)
> 
> I don't remember having seen something similar in other pages.
> 
> I think defining a macro in uapi headers could be the right thing to
> do.  Something like LANDLOCK_ACCESS_FS_RIGHTS_MASK_ABI_{1,2,3} or
> other similar name?

Noted it on my TODO list - it's probably best discussed on the kernel
list whether this is the right approach.


> > 1) Make assumptions about the numbers, for brevity
> >    (as done in the patch I sent).
> > 
> >    [...]
> > 
> > 2) Use the constants from the header and OR them.
> > 
> >    [...]
> > 
> > 3) Third option is the middle way,
> >    naming the "highest" known access right for each ABI version:
> > 
> > __u64 landlock_fs_access_rights[] = {
> >     (LANDLOCK_ACCESS_FS_MAKE_SYM << 1) - 1,  /* ABI v1                 */
> >     (LANDLOCK_ACCESS_FS_REFER << 1) - 1,     /* ABI v2: add "refer"    */
> >     (LANDLOCK_ACCESS_FS_TRUNCATE << 1) - 1,  /* ABI v3: add "truncate" */
> > }
> 
> I'm not sure if I like this one.  I'll leave it up to you to decide
> the one you like.  :)

I'll ponder it a bit and send a new patch soon.

Mickaël, do you have any opinions/preferences on this?

–Günther