Hello Miklos,
I'm working on some better documentation of mount namespaces,
and there's a detail that puzzles me, and I hope you might be
able to help, since you added the detail...
In Documentation/filesystems/proc.txt there is this text in the
description of /proc/PID/mountinfo:
[[
Parsers should ignore all unrecognised optional fields. Currently the
possible optional fields are:
shared:X mount is shared in peer group X
master:X mount is slave to peer group X
propagate_from:X mount is slave and receives propagation from peer group X (*)
unbindable mount is unbindable
(*) X is the closest dominant peer group under the process's root. If
X is the immediate master of the mount, or if there's no dominant peer
group under the same root, then only the "master:X" field is present
and not the "propagate_from:X" field.
]]
What is a dominant peer group, as distinct from the immediate master?
I can see in fs/proc_namespaces.c that there is this distinction made:
[[
/* Tagged fields ("foo:X" or "bar") */
if (IS_MNT_SHARED(r))
seq_printf(m, " shared:%i", r->mnt_group_id);
if (IS_MNT_SLAVE(r)) {
int master = r->mnt_master->mnt_group_id;
int dom = get_dominating_id(r, &p->root);
seq_printf(m, " master:%i", master);
if (dom && dom != master)
seq_printf(m, " propagate_from:%i", dom);
}
]]
But I can't relate that to some user-space semantics. I suppose another
way of asking my question is: how could I create a slave that is
propagating from a peer group other than it's immediate master?
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
