Michael Tokarev wrote:
Neil Brown wrote:
On Monday July 3, bluca@xxxxxxxxxx wrote:
Hello,
the following patch aims at solving an issue that is confusing a lot of
users.
when using udev, device files are created only when devices are
registered with the kernel, and md devices are registered only when
started.
mdadm needs the device file _before_ starting the array.
so when using udev you must add --auto=yes to the mdadm commandline or
to the ARRAY line in mdadm.conf
following patch makes auto=yes the default when using udev
The principle I'm reasonably happy with, though you can now make this
the default with a line like
CREATE auto=yes
in mdadm.conf.
However....
+
+ /* if we are using udev and auto is not set, mdadm will almost
+ * certainly fail, so we force it here.
+ */
+ if (autof == 0 && access("/dev/.udevdb",F_OK) == 0)
+ autof=2;
+
I'm worried that this test is not very robust.
On my Debian/unstable system running used, there is no
/dev/.udevdb
though there is a
/dev/.udev/db
I guess I could test for both, but then udev might change
again.... I'd really like a more robust check.
Why to test for udev at all? If the device does not exist, regardless
if udev is running or not, it might be a good idea to try to create it.
Because IT IS NEEDED, period. Whenever the operation fails or not, and
whenever we fail if it fails or not - it's another question, and I think
that w/o explicit auto=yes, we may ignore create error and try to continue,
and with auto=yes, we fail on create error.
I have to agree here, I can't think of a case where creation of the
device name would not be desirable, udev or no. But to be cautious,
perhaps the default should be to create the device if the path starts
with /dev/ or /tmp/ unless auto creation is explicitly off. I don't
think udev or mount points come into the default decision at all, there
are just too many options on naming.
Note that /dev might be managed by some other tool as well, like mudev
from busybox, or just a tiny shell /sbin/hotplug script.
Note also that the whole root filesystem might be on tmpfs (like in
initramfs), so /dev will not be a mountpoint.
Agree with both points.
Also, I think mdadm should stop creating strange temporary nodes somewhere
as it does now. If /dev/whatever exist, use it. If not, create it (unless,
perhaps, auto=no is specified) directly with proper mknod("/dev/mdX"), but
don't try to use some temporary names in /dev or elsewhere.
True, but I don't see a case where this would be useful. And if it is,
then add an auto=obscure_names option for the case where you really want
that behaviour.
In case of nfs-mounted read-only root filesystem, if someone will ever need
to assemble raid arrays in that case.. well, he can either prepare proper
/dev on the nfs server, or use tmpfs-based /dev, or just specify /tmp/mdXX
instead of /dev/mdXX - whatever suits their needs better.
Because /dev and /tmp are well known special cases, I would default auto
for them. In other cases explicit behavior could be specified.
Feel free to point out something bad which occurs by using this default
behavior.
--
bill davidsen <davidsen@xxxxxxx>
CTO TMR Associates, Inc
Doing interesting things with small computers since 1979
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