On 11/18/2011 03:26 AM, Tom Gundersen wrote:
On Fri, Nov 18, 2011 at 1:03 PM, Dave Reisner<[email protected]> wrote:
On Thu, Nov 17, 2011 at 10:51:37PM -0300, Gerardo Exequiel Pozzi wrote:
On 11/17/2011 10:21 PM, Dave Reisner wrote:
On Fri, Nov 18, 2011 at 11:42:43AM +1100, Tom Gundersen wrote:
On Fri, Nov 18, 2011 at 5:23 AM, Thomas Bächler<[email protected]> wrote:
Am 17.11.2011 18:07, schrieb Tom Gundersen:
I see two potential issues: boot speed and memory use. Moving stuff
around in memory should be pretty much instantaneous, and the memory
(a couple of MB) will be swapped out quick enough so it shouldn't make
a difference.
I'd be happy to write a new patch where this is optional, but I don't
think we should optimize for stuff unless we know it is a measurable
problem.
Depending on what's in there, it could be big. For example, I once wrote
a hook that extracted a tarfile that was stored inside initramfs (that
tarfile was the whole root filesystem IIRC).
That's something to take into consideration. I think it would be best
if we were able to optimize the cases that need it by adding some
exceptions to the copying, but still keep the bits needed for
shutdown++, rather than disabling it altogether. Having huge
initramfs' being a corner case, any workaround should of course be
unintrusive (if that is not possible then I agree on just allowing
this stuff to be switched off).
[untested: would bindmounting a directory (like say /lib/modules) to
itself exclude it from "cp -ax"?]
No, it won't. Generally, detection of crossing onto another mount is
done by comparing the devno of '.' to the devno of '..'. Bind mounts
aren't special in this regard -- they'll just expose the underlying
physical mount.
Mmm no, you can not access to files in underliying mount from such path.
Anyway the rootfs is the HEAD of vfsmount, so you can not
bind/move/pivot. :P
But supose that you can do a bindmount... -a is used that implies
-d, that implies --preserve=links, in that case cp will fails
because will try to create a link to directory. ;)
No, this has nothing to do with chrooting. The point is that if you're
walking through a directory structure for an operation that's required
to stay on a single filesystem, you're stat'ing every directory before
descending into it (my example was actually backwards). Written in
(probably nonworking) shell..
walk() {
local pwd_dev dir_dev
pwd_dev=$(stat -c %d "$1")
for f in *; do
if [[ -d $f ]]; then
dir_dev=$(stat -c "$1/$f")
if (( pwd_dev != dir_dev )); then
# this is a mountpoint, skip it
continue
fi
walk "$f"
else
callback "$f"
fi
done
}
walk /
Why no just copy the needed files? Yes needs more steps...
Because I don't want to have to calculate what's needed for teardown on
an encrypted LVM root device. Make it optional, and everything is
copasetic.
Thanks for the explanations Dave and Gerardo.
I agree that it would be best to just copy everything, which would not
require us to do anything fancy.
Still not sold on making it optional though. At least wait until
someone can point to a use-case and some numbers that shows a real
problem. If the initramfs is sufficiently huge, the time taken to copy
it to /run would obviously be measurable. However, the time taken to
extract the initramfs in the first place would probably dwarf this
number.
If we start making things optional we'd have something like this:
copying /run/initramfs is required by "shutdown" and "shutdown" is
required by "usr".
But all users who have a separate /usr must use the "usr" hook, and
all users really should use the "shutdown" hook. So unless we find a
case where including a hook causes some sort of real downside I'd say
just make it unconditional, and thereby reduce the number of
configurations we'd have to test.
> From the point of view of initscripts it would be very nice to know
that /usr is always mounted, and if the rootfs is on lvm or something
like that it will always be torn down properly, without worrying about
users possibly disabling these hooks in mkinitcpio.
Just my two cents.
-t
You are welcome!
Note that you can bind mount some dir (outside rootfs) for example in
/run, the overlap /lib/modules.
Anyway the copy can be done at end of init just before switch_root, just
after udev stopped. so you can rm -r /lib/modules ; cp -ax / /run/initramfs
PS: uncompressed archiso.img is 22M.
--
Gerardo Exequiel Pozzi
\cos^2\alpha + \sin^2\alpha = 1
