Re: [PATCH V6 00/10] namespaces: log namespaces per task

From: Eric W. Biederman
Date: Mon Apr 27 2015 - 22:21:07 EST

Richard Guy Briggs <rgb@xxxxxxxxxx> writes:

> On 15/04/24, Eric W. Biederman wrote:
>> Richard Guy Briggs <rgb@xxxxxxxxxx> writes:
>> > On 15/04/22, Richard Guy Briggs wrote:
>> >> On 15/04/20, Eric W. Biederman wrote:
>> >> > Richard Guy Briggs <rgb@xxxxxxxxxx> writes:
>> >> >
>> >
>> > Do I even need to report the device number anymore since I am concluding
>> > s_dev is never set (or always zero) in the nsfs filesystem by
>> > mount_pseudo() and isn't even mountable?
>> We still need the dev. We do have a device number get_anon_bdev fills it in.
> Fine, it has a device number. There appears to be only one of these
> allocated per kernel. I can get it from &nsfs->fs_supers (and take the
> first instance given by hlist_for_each_entry and verify there are no
> others). Why do I need it, again?

Because if we have to preserve the inode number over a migration event I
want to preserve the fact that we are talking about inode numbers from a
superblock with a device number.

Otherwise known as I am allergic to kernel global identifiers, because
they can be major pains. I don't want to have to go back and implement
a namespace for namespaces.

>> >> They are all covered:
>> >> sys_unshare > unshare_userns > create_user_ns
>> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_mnt_ns
>> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_utsname > clone_uts_ns
>> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_ipcs > get_ipc_ns
>> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_pid_ns > create_pid_namespace
>> >> sys_unshare > unshare_nsproxy_namespaces > create_new_namespaces > copy_net_ns
>> Then why the special change to fork? That was not reflected on
>> the unshare path as far as I could see.
> Fork can specify more than one CLONE flag at once, so collecting them
> all in one statementn seemed helpful. setns can only set one at a time.

unshare can also specify more than one CLONE flag at once.

I just pointed that out becase that seemed really unsymmetrical.

> Ok, understood, we can't just punt this one to a higher layer...
> So this comes back to a question above, which is how do we determine
> which device it is from? Sounds like we need something added to
> ns_common or one of the 6 namespace types structs.

Or we can just hard code reading it off of the appropriate magic
filesystem. Probably what we want is a well named helper function that
does the job.

I just care that when we talk about these things we are talking about
inode numbers from a superblock that is associated with a given device
number. That way I don't have nightmares about dealing with a namespace
for namespaces.

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