Re: User-visible context-mount API

On Tue, Jan 16, 2018 at 10:10:12AM +0000, David Howells wrote:

Inside the kernel the MS_* flags appear to belong to a number of fundamentally
different classes:

Good point, but I'm not sure about your terminology -- for example
"topology" sounds strange if we use "propagation" for years.

 (1) Things like MS_SILENT and MS_REMOUNT which affect the behaviour of the
     mount process, but aren't persistent beyond that.

 mount-operation flags  (now including MS_BIND too)

 (2) Inter-namespace topology management, controlling how mounts are shared
     and duplicated between namespaces.

 propagation flags

 (3) Restrictions on accesses through a particular mountpoint, eg. MS_NODEV,
     MS_NOEXEC.

 VFS flags (now including MS_BIND|MS_REMOUNT|MS_RDONLY too)

 (4) Instructions to a filesystem on how a superblock is to behave.

 FS flags

I think the classes are fundamentally different - and we've already separated
(4) from the others inside the kernel.  However, I've no great objection to
keeping (2) and (3) together in the same mask.  It just sounds cleaner to
separate them. 

 I agree.

    Karel

-- 
 Karel Zak  [off-list ref]
 http://karelzak.blogspot.com