Re: [Virtio-fs] [PATCH] virtiofsd: Show submounts

[Miklos Szeredi]

On Wed, Apr 29, 2020 at 10:31 AM Max Reitz <address@hidden> wrote:
>
> On 28.04.20 21:15, Dr. David Alan Gilbert wrote:

> > So are you saying we need a:
> >        if (mount(NULL, "/", NULL, MS_REC | MS_SHARED, NULL) < 0) {
> >
> >   and can this go straight after (1) ?
>
> Isn’t MS_SHARED and MS_SLAVE mutually exclusive, that is, both are just
> different propagation types?  So shouldn’t putting this after (1) be
> effectively the same as replacing (1)?

No, think of it more like a set of groups (mounts in a group have the
same "shared:$ID" tag in /proc/self/mountinfo) and these groups being
arranged into a tree, where child groups get propagation from the
parent group (mounts have a "master:$PARENT_ID" tag), but not the
other way round.

So if a mount is part of a shared group and this group is also the
child of another shared group, then it will have both a "shared:$ID"
and a "master:$PARENT_ID" tag in /proc/self/mountinfo.

For the gory details see Documentation/filesystems/sharedsubtree.txt

Thanks,
Miklos