On Tue, Apr 28, 2009 at 20:45, Alasdair G Kergon <agk@xxxxxxxxxx> wrote:
> On Tue, Apr 28, 2009 at 07:41:10PM +0200, Kay Sievers wrote:
>> Please do not rename kernel devices, they should match the kernel
>> names. Only create SYMLINK+= to the kernel names, or change the kernel
>> to ceate the proper names, which will not work I guess, so please
>> leave them as they are today.
>
>> In general we do not want any unneeded disconnect from kernel names
>> and /dev names, and dm block devices should stay as /dev/dm-* device
>> nodes.
>
> The /dev/dm-* devices have been a support headache for us. I don't know
> how they first sneaked into some distros but I maintain that dm-* are
> internal kernel names only of use for debugging purposes and the average
> sysadmin should never have to encounter them. If I had my way they
> would never have become visible to userspace. (Unfortunately the size
> restriction on the field prevents us from replacing them with our
> preferred names within the kernel, unless that's changed since
> I last looked.)
There is no size limit anymore.
> There is nothing fundamental about dm-*, they are meaningless to the
> user, absolutely not persistent across boots and tools may need to
> change what they mean whenever there is some reconfiguration. Their
> presence causes no end of problems as they 'leak' out into initrds,
> fstabs, error messages etc. On a normal, functioning system, absolutely
> nothing in userspace should ever reference them.
No, the kernel logs use these names, and therefore we want these names
in /dev too.
> The namespace for dm devices is currently *only* under /dev/mapper.
No, not the last years, since udev. The /dev/mapper/ nodes are racy
and wrongly timed to use in hotplug setups. Most people who do
hotplug-like stuff with dm use the /dev/by-id/dm-{uuid,name}* links
because they are reliably created timing wise.
> If people *really* think dm devices need to appear directly in a flat
> namespace in /dev (why?) then we should drop the /dev/mapper directory
> and move them to /dev/mapper-vg1-lvol1 for example. (The whole strength
> of udev is that it makes it easy to do something like that, in fact.)
Sure, but there is still not enough reason to be different from the
kernel name. You support rename, that should never happen, that a
device node needs to be renamed, if the kernel does not change the
device name.
> Alternatively, we could see about making dm uuids mandatory and
> go for something like /dev/dm-<uuid>.
Sounds fine, as long as the /dev names match the kernel devices. I
suggest you change the kernel to use the names right away, or go for
symlinks in /dev/mapper/, like some people already do with the dm/udev
integration hack, which gets hopefully replaced by the new stuff you
are coming up with.
Thanks,
Kay
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