How to find the root partition with root=dhcp root-path=iscsi:::...

How to find the root partition with root=dhcp root-path=iscsi:::...

[Harald Hoyer]

If we have root=dhcp and root-path from dhcp with "iscsi::... " nothing is know 
about the partition where root lives in.

RFC:
provide a pre-mount fallback, which tries to mount

/dev/disk/by-label/\x2f (LABEL=/)
/dev/disk/by-label/ROOT (LABEL=ROOT)


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Re: How to find the root partition with root=dhcp root-path=iscsi:::...

[Warren Togami]

On 06/18/2009 10:30 AM, Harald Hoyer wrote:
> If we have root=dhcp and root-path from dhcp with "iscsi::... " nothing
> is know about the partition where root lives in.
>
> RFC:
> provide a pre-mount fallback, which tries to mount
>
> /dev/disk/by-label/\x2f (LABEL=/)
> /dev/disk/by-label/ROOT (LABEL=ROOT)

I think this was the intent of netroot=dhcp for remote block device 
protocols, then you can define something else in root=.  Whether it is 
implemented yet I don't know.

Warren
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Re: How to find the root partition with root=dhcp root-path=iscsi:::...

[Harald Hoyer]

On 06/18/2009 06:06 PM, Warren Togami wrote:
> On 06/18/2009 10:30 AM, Harald Hoyer wrote:
>> If we have root=dhcp and root-path from dhcp with "iscsi::... " nothing
>> is know about the partition where root lives in.
>>
>> RFC:
>> provide a pre-mount fallback, which tries to mount
>>
>> /dev/disk/by-label/\x2f (LABEL=/)
>> /dev/disk/by-label/ROOT (LABEL=ROOT)
>
> I think this was the intent of netroot=dhcp for remote block device
> protocols, then you can define something else in root=. Whether it is
> implemented yet I don't know.
>
> Warren

Well, but the root-path does not specify the root partition!
Either we extend the iscsi:::: spec with a root partition or we make 
requirements like I did above.
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Re: How to find the root partition with root=dhcp root-path=iscsi:::...

[Warren Togami]

On 06/18/2009 01:01 PM, Harald Hoyer wrote:
> On 06/18/2009 06:06 PM, Warren Togami wrote:
>> On 06/18/2009 10:30 AM, Harald Hoyer wrote:
>>> If we have root=dhcp and root-path from dhcp with "iscsi::... " nothing
>>> is know about the partition where root lives in.
>>>
>>> RFC:
>>> provide a pre-mount fallback, which tries to mount
>>>
>>> /dev/disk/by-label/\x2f (LABEL=/)
>>> /dev/disk/by-label/ROOT (LABEL=ROOT)
>>
>> I think this was the intent of netroot=dhcp for remote block device
>> protocols, then you can define something else in root=. Whether it is
>> implemented yet I don't know.
>>
>> Warren
>
> Well, but the root-path does not specify the root partition!
> Either we extend the iscsi:::: spec with a root partition or we make
> requirements like I did above.

root= cannot specify the root partition?

In any case, nothing really stops us from extending the iscsi RFC spec 
if we really want to.

Warren Togami
wtogami-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org
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Re: How to find the root partition with root=dhcp root-path=iscsi:::...

[Warren Togami]

On 06/18/2009 10:30 AM, Harald Hoyer wrote:
> If we have root=dhcp and root-path from dhcp with "iscsi::... " nothing
> is know about the partition where root lives in.
>
> RFC:
> provide a pre-mount fallback, which tries to mount
>
> /dev/disk/by-label/\x2f (LABEL=/)
> /dev/disk/by-label/ROOT (LABEL=ROOT)
>

BTW, I'm not against this as a fallback, but am I incorrect about root= 
being explicitly usable with netroot=dhcp?

Warren
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Re: How to find the root partition with root=dhcp root-path=iscsi:::...

[David Dillow]

On Thu, 2009-06-18 at 19:01 +0200, Harald Hoyer wrote:
> On 06/18/2009 06:06 PM, Warren Togami wrote:
> > On 06/18/2009 10:30 AM, Harald Hoyer wrote:
> >> If we have root=dhcp and root-path from dhcp with "iscsi::... " nothing
> >> is know about the partition where root lives in.
> >>
> >> RFC:
> >> provide a pre-mount fallback, which tries to mount
> >>
> >> /dev/disk/by-label/\x2f (LABEL=/)
> >> /dev/disk/by-label/ROOT (LABEL=ROOT)
> >
> > I think this was the intent of netroot=dhcp for remote block device
> > protocols, then you can define something else in root=. Whether it is
> > implemented yet I don't know.
> >
> > Warren
> 
> Well, but the root-path does not specify the root partition!
> Either we extend the iscsi:::: spec with a root partition or we make 
> requirements like I did above.

The RFC only says we need to boot off the LUN specified, 0 if none
listed. That's your default partition.

It's workable, as these can be virtual disks anyways, but as Warren
mentions, we can extend the RFC.

Also, you can specify root=LABEL=ROOT or root=/dev/sda1 etc and it
should work, or at least it used to with the netroot= code. I haven't
tested it this week -- vacation.
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Re: How to find the root partition with root=dhcp root-path=iscsi:::...

[Harald Hoyer]

On 06/19/2009 04:55 AM, David Dillow wrote:
> On Thu, 2009-06-18 at 19:01 +0200, Harald Hoyer wrote:
>> On 06/18/2009 06:06 PM, Warren Togami wrote:
>>> On 06/18/2009 10:30 AM, Harald Hoyer wrote:
>>>> If we have root=dhcp and root-path from dhcp with "iscsi::... " nothing
>>>> is know about the partition where root lives in.
>>>>
>>>> RFC:
>>>> provide a pre-mount fallback, which tries to mount
>>>>
>>>> /dev/disk/by-label/\x2f (LABEL=/)
>>>> /dev/disk/by-label/ROOT (LABEL=ROOT)
>>> I think this was the intent of netroot=dhcp for remote block device
>>> protocols, then you can define something else in root=. Whether it is
>>> implemented yet I don't know.
>>>
>>> Warren
>> Well, but the root-path does not specify the root partition!
>> Either we extend the iscsi:::: spec with a root partition or we make
>> requirements like I did above.
>
> The RFC only says we need to boot off the LUN specified, 0 if none
> listed. That's your default partition.

ok, so the LUN is the partition number?
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Re: How to find the root partition with root=dhcp root-path=iscsi:::...

[David Dillow]

On Fri, 2009-06-19 at 08:21 +0200, Harald Hoyer wrote:
> On 06/19/2009 04:55 AM, David Dillow wrote:
> > The RFC only says we need to boot off the LUN specified, 0 if none
> > listed. That's your default partition.
> 
> ok, so the LUN is the partition number?

No, a LUN is a whole disk. You would map the LUN to /dev/sda or /dev/sdb
or such depending on which one it is, and use the entire disk -- no
partitions needed. If you wanted to separate /var or /home etc, you
would put them on a different LUN(s) -- partitions optional -- and
use /etc/fstab to mount them.
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Re: How to find the root partition with root=dhcp root-path=iscsi:::...

[Harald Hoyer]

On 06/19/2009 06:05 PM, David Dillow wrote:
> On Fri, 2009-06-19 at 08:21 +0200, Harald Hoyer wrote:
>> On 06/19/2009 04:55 AM, David Dillow wrote:
>>> The RFC only says we need to boot off the LUN specified, 0 if none
>>> listed. That's your default partition.
>> ok, so the LUN is the partition number?
>
> No, a LUN is a whole disk. You would map the LUN to /dev/sda or /dev/sdb
> or such depending on which one it is, and use the entire disk -- no
> partitions needed. If you wanted to separate /var or /home etc, you
> would put them on a different LUN(s) -- partitions optional -- and
> use /etc/fstab to mount them.

hmm, so I would have to create a rule, which would look for the next disk which 
appears and has some /sys magic iSCSI attributes  and try to mount the whole disk.
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Re: How to find the root partition with root=dhcp root-path=iscsi:::...

[David Dillow]

On Fri, 2009-06-19 at 18:40 +0200, Harald Hoyer wrote:
> On 06/19/2009 06:05 PM, David Dillow wrote:
> > On Fri, 2009-06-19 at 08:21 +0200, Harald Hoyer wrote:
> >> On 06/19/2009 04:55 AM, David Dillow wrote:
> >>> The RFC only says we need to boot off the LUN specified, 0 if none
> >>> listed. That's your default partition.
> >> ok, so the LUN is the partition number?
> >
> > No, a LUN is a whole disk. You would map the LUN to /dev/sda or /dev/sdb
> > or such depending on which one it is, and use the entire disk -- no
> > partitions needed. If you wanted to separate /var or /home etc, you
> > would put them on a different LUN(s) -- partitions optional -- and
> > use /etc/fstab to mount them.
> 
> hmm, so I would have to create a rule, which would look for the next disk which 
> appears and has some /sys magic iSCSI attributes  and try to mount the whole disk.

You're looking for the disk that makes the directory
/sys/class/scsi_disk/<HOST>:0:0:<LUN>

HOST will almost always be 0, unless we try multiple iSCSI roots in
sequence. LUN will be the one specified by root-path.

I'm not sure if you can match this via udev rules, perhaps using a match
rule such as SYMLINK=="by-path/*-scsi-0:0:0:<LUN>"
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