Re: [PATCH 24/32] vfs: syscall: Add fsopen() to prepare for superblock creation [ver #9]

[Andy Lutomirski]

On Fri, Jul 13, 2018 at 8:40 AM, David Howells <dhowells@xxxxxxxxxx> wrote:
> Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>
>> > Whilst I'm at it, do we want the option of doing the equivalent of
>> > mountat()?  I.e. offering the option to open all the device files used by
>> > a superblock with dfd and AT_* flags in combination with the filename?
>> >
>>
>> Isn't that more or less what I was suggesting?
>
> Yes, you suggested that.  I'm asking if we actually need that.
>

Suppose some program in a container chroots itself and then tries to
create an fscontext backed by "/path/to/blockdev".  The syscall gets
intercepted by a container manager.  That manager now has a somewhat
awkward time of mounting the same fs, although it could use
"/proc/PID/root/path/to/blockdev", I suppose.  Even that approach has
some potentially awkward permission issues.  I would defer to the
people who actually write software like this, but I can imagine fds
being considerably easier to work with.