Re: [REVIEW v3] Storage mounting API
On Tue, Mar 19, 2013 at 10:38:16AM +0100, Jan Synacek wrote:
On 03/19/2013 09:30 AM, Jan Safranek wrote:
> On 03/18/2013 03:31 PM, Jan Synacek wrote:
>> [ Description (
>> "If not NULL, specifies a directory path where a part of the
original "
>> "file hierarchy is remounted. Also signifies use of a bind
mount." ) ]
>> string BindDir;
>
> Huh? What is 'original hierarchy'? Is it source directory of the bind
> mount? Can we merge it with FileSystemType='bind' and
> FileSystemSpec='/bind/source'?
Unfortunate wording, I admit. I'll try to fix that.
I think that FileSystemType=bind makes no sense as bind is not a filesystem
type is "none", "bind" is mount flag
type. It's just a remount of *the same filesystem* to somewhere
else. Or am I
missing something?
I have doubts that introduce something like BindDir is a good idea.
It would be better to not think about "bind" as about something
special. The bind *operation* creates a new connection between
a filesystem and target (mountpoint). That's all.
mount /dev/sda1 /foo
mount /dev/sda2 /bar
is the same as:
mount /dev/sda1 /foo
mount --bind /foo /bar
the difference is that by bind operation you can mount non-root
directory of the filesystem, for example:
mount --bind /foo/subdir /bar
(the same thing is possible by btrfs subvolumes).
The important is that the "original" mountpoint could be unmounted.
There is not any dependence between the mountpoints (e.g. between /foo
and /bar).
mount /dev/sda1 /foo
mount --bind /foo /bar
umount /foo
rm -rf /foo
The generic rule is to not try to save any information about the current
VFS status somewhere in userspace. If you want to know the current
setting used by your system then always see /proc/self/mountinfo.
Everything else is bogus. We really don't want to introduce another
/etc/mtab :-)
Karel
--
Karel Zak <kzak(a)redhat.com>
http://karelzak.blogspot.com