A fuse based initfs

[Douglas McClendon]

Jon Nettleton wrote:
> On 8/23/07, Jon Nettleton <jon.nettleton at gmail.com> wrote:
>> On 8/23/07, Andrew Bartlett <abartlet at samba.org> wrote:
>>> On Thu, 2007-08-23 at 18:02 -0400, Jon Nettleton wrote:
>>>> On 8/22/07, Douglas McClendon <dmc.fedora at filteredperception.org> wrote:
>>>>> In general, it sounds like you are outlining several different
>>>>> problem/solutions, but I don't think they all need to be as tightly
>>>>> integrated as you suggest.
>>>>>
>>>>> For instance, the gdm in initramfs (or very very early).  Why do you
>>>>> need this copy-on-write rootfs stuff?  Why not just have a tmpfs, and a
>>>>> gdm configuration that looks there.  Likewise for the early logging
>>>>> stuff.  Later during boot, the early-boot logfiles in tmpfs can be
>>>>> copied to /var/log.  This isn't as nice as the magic
>>>>> unionfs/dm-snapshot-merge automagic merging.  But I don't think that is
>>>>> necessary and worth the steps you are taking to get it.
>>>> The problem is that all the X gdm talk is through fifo sockets.  This
>>>> busies the filesystems
>>>> and makes it impossible to just copy things around.  If we want the
>>>> boot process to be
>>>> smooth and seamless we are going to need some sort of ability to write
>>>> to a "read only" filesystem in place.
>>> Why not just put the fifo on a tmpfs, and keep it around for the life of
>>> the system.  Being tmpfs, it cleans up nicely when shut down.  There are
>>> many other reasons to move the X socket from /tmp (selinux etc).
>>>
>>> Would a permanent symlink from /tmp -> a tmpfs mounted on /var/run/X
>>> solve the legacy issues?
>>>
>> That only leaves some log issues.  However if other people have no
>> problems with /var/run/X and /var/run/gdm being tmpfs or ramfs then
>> this is do-able.
>>
> 
> actually thinking about this.  Moving these files to a tmpfs/ramfs
> filesystem will actually allow us to remove a bunch of cleanup code in
> rc.sysinit for stale filehandles and directories.
> 
> hmmm...this is sounding better by the minute.

Over on fedora-livecd-list, I'm working on using something like a 
usbstick instead of ram for the read-write overlay on top of the 
read-only ext3fs image (that is on the livecd, living in a squashfs).

One of the issues was getting things unmounted cleanly at shutdown. 
While one gross method I used, turned out to not be necessary or the 
right approach, while talking about it, the rather logical idea came up 
of keeping the original initramfs around, and using it to tear things 
down, just as it is used to build things up.

E.g. to eject the livecd at shutdown.  You need the eject command, and a 
completely unmounted rootfs.  Using a tmpfs, or perhaps more logically, 
using the tmpfs from the original initramfs, seems like the way to do this.

And that seems like it might mesh well with the idea of gdm in initramfs 
  that I think you are talking about.

(and maybe somebody can correct me, but does the original initramfs 
really, truly get unmounted currently?  Or is it just lazy unmounted, 
and it is really hanging around hidden somewhere?)

-dmc