Re: [DNG] Purpose of an OS: was network device naming (was: What can I do after netman?)

[karl]

Steve:
> On Sun,  4 Oct 2015 00:08:58 +0200 (CEST)
> k...@aspodata.se wrote:
> > Hendrik:
> > > Hendrik Boom  wrote:
> > > > Can we agree that ww shouldnn't have to change our configurations
> > > > if we do not change anything in the hardware?
> > > That would be a reasonable base requirement.
> > What if I have say 5 disks /dev/sd[a-e]; if someone accidentally
> > pulled out /dev/sdc, and oops put it back before anyone noticed;
> > should it show up again as /dev/sdc or should it be /dev/sdf ?
> This is why you use UUID= or LABEL= in /etc/fstab.

Let's face it, thoose other names of the device is just symlinks, do a
find /dev/disk/ | xargs ls -ld and you will find only dirs. and 
softlinks. But if the disk is mounted we are past that stage.

So that will only help you when the partition is to be mounted or when
you want to unmount it, after all, fstab and /dev/-names are just
for the user space. The kernel mostly only cares about the maj/min
numbers, or am I wrong?

What happens when you unplug your root fs, wait a few seconds till
the kernel gives up and then plug it in again ?

Regards,
/Karl Hammar

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Re: [DNG] Purpose of an OS: was network device naming (was: What can I do after netman?)

[Hendrik Boom]

On Sat, Oct 03, 2015 at 08:49:04AM +0100, Simon Hobson wrote:
> poitr pogo  wrote:
> 
> > > I thought it was stupid for other reasons, but now that you mention it,
> > 
> > > yeah, naming it after the particular slot into which it's plugged in is
> > > stupid, and if you take the box apart and move things around, you can
> > > break your OS.
> > >
> > 
> > no. it is not stupid. it is the most reasonable way. one can replace a part 
> > and do not have to touch any system config.
> 
> And the flip side is that you can't move anything without the name changing. 
> Plug the USB-[ethernet|wifi] adapter into a different orifice and it's now 
> got a different name. Move an ethernet card because you want that slot for 
> something different and it's now got a different name.
> 
> > device by manufactuter name or model name or serial. this is stupid.
> 
> No more or less stupid than by physical location. Eg, taking the above 
> mentioned USB adapter - if you use it's serial number then it keeps it's name 
> regardless of which socket it's plugged into, vs changing name depending on 
> where it's plugged in.
> 
> As I've mentioned before, I know that the Windows guys at work have had the 
> problem where the customer/end user plugs the backup drive into a different 
> USB port and the backups fail. So I believe we normally tell them to leave 
> the cable attached to the computer.
> 
> 
> Lets face it - there is no "right" answer to this other than a system with 
> enough intelligence to read the user/admin's mind and work out what they 
> intend to happen - and I think we're a bit off that yet !
> Looking back, I think I've "moved" something at least as often as I've 
> replaced it with a different something in the same location - probably more 
> in fact.

Can we agree that ww shouldnn't have to change our configurations if we 
do not change anything in the hardware?

-- hendrik
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Re: [DNG] Purpose of an OS: was network device naming (was: What can I do after netman?)

[Simon Hobson]

Hendrik Boom  wrote:

> Can we agree that ww shouldnn't have to change our configurations if we 
> do not change anything in the hardware?

That would be a reasonable base requirement.

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Re: [DNG] Purpose of an OS: was network device naming (was: What can I do after netman?)

[Steve Litt]

On Sun,  4 Oct 2015 00:08:58 +0200 (CEST)
k...@aspodata.se wrote:

> Hendrik:
> > Hendrik Boom  wrote:
> > 
> > > Can we agree that ww shouldnn't have to change our configurations
> > > if we do not change anything in the hardware?
> > 
> > That would be a reasonable base requirement.
> 
> What if I have say 5 disks /dev/sd[a-e]; if someone accidentally
> pulled out /dev/sdc, and oops put it back before anyone noticed;
> should it show up again as /dev/sdc or should it be /dev/sdf ?

This is why you use UUID= or LABEL= in /etc/fstab.

SteveT
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Re: [DNG] Purpose of an OS: was network device naming (was: What can I do after netman?)

[karl]

Hendrik:
> Hendrik Boom  wrote:
> 
> > Can we agree that ww shouldnn't have to change our configurations if we 
> > do not change anything in the hardware?
> 
> That would be a reasonable base requirement.

What if I have say 5 disks /dev/sd[a-e]; if someone accidentally pulled 
out /dev/sdc, and oops put it back before anyone noticed; should it 
show up again as /dev/sdc or should it be /dev/sdf ?

Regards,
/Karl Hammar

---
Aspö Data
Lilla Aspö 148
S-742 94 Östhammar
Sweden
+46 173 140 57


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Re: [DNG] Purpose of an OS: was network device naming (was: What can I do after netman?)

[Simon Hobson]

poitr pogo  wrote:

> > I thought it was stupid for other reasons, but now that you mention it,
> 
> > yeah, naming it after the particular slot into which it's plugged in is
> > stupid, and if you take the box apart and move things around, you can
> > break your OS.
> >
> 
> no. it is not stupid. it is the most reasonable way. one can replace a part 
> and do not have to touch any system config.

And the flip side is that you can't move anything without the name changing. 
Plug the USB-[ethernet|wifi] adapter into a different orifice and it's now got 
a different name. Move an ethernet card because you want that slot for 
something different and it's now got a different name.

> device by manufactuter name or model name or serial. this is stupid.

No more or less stupid than by physical location. Eg, taking the above 
mentioned USB adapter - if you use it's serial number then it keeps it's name 
regardless of which socket it's plugged into, vs changing name depending on 
where it's plugged in.

As I've mentioned before, I know that the Windows guys at work have had the 
problem where the customer/end user plugs the backup drive into a different USB 
port and the backups fail. So I believe we normally tell them to leave the 
cable attached to the computer.


Lets face it - there is no "right" answer to this other than a system with 
enough intelligence to read the user/admin's mind and work out what they intend 
to happen - and I think we're a bit off that yet !
Looking back, I think I've "moved" something at least as often as I've replaced 
it with a different something in the same location - probably more in fact.



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Re: [DNG] Purpose of an OS: was network device naming (was: What can I do after netman?)

[poitr pogo]

29-09-2015 16:48, "Steve Litt"  napisał(a):
>

> I thought it was stupid for other reasons, but now that you mention it,
> yeah, naming it after the particular slot into which it's plugged in is
> stupid, and if you take the box apart and move things around, you can
> break your OS.
>

no. it is not stupid. it is the most reasonable way. one can replace a part
and do not have to touch any system config.
but that's too hard to locate a part for common desktop user and we get a
user frienfly system which is bound tight to the detsils of the hardware it
is using and have to reconfigure itself every time new part is added. even
temporary. and finaly another layer of abstraction is invented, dynamic
reconfiguration instead. all to speed up boot process.

device by manufactuter name or model name or serial. this is stupid.

--
piotr
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Re: [DNG] Purpose of an OS: was network device naming (was: What can I do after netman?)

[Simon Hobson]

Steve Litt  wrote:

>> The whole point of having 'an operating system'
>> is that it provides an abstract interface userspace software can use
>> to interact with the physical components of a different computer
>> according to the functions they're supposed to be provide, regardless
>> of the way this particular computer happens to be assembled.
> 
> Does anyone else agree with me that in the preceding sentence Rainer
> encapsulated the entire philosophy of people desiring simple and
> logical software? Rainer, can I quote your preceding sentence elsewhere?

It seems a good summary to me.


>> Considering this, encoding details of the bus layout and current bus
>> configuration in network interface names is just profoundly stupid.
> 
> I thought it was stupid for other reasons, but now that you mention it,
> yeah, naming it after the particular slot into which it's plugged in is
> stupid, and if you take the box apart and move things around, you can
> break your OS.

Unfortunately, I think this is one of those areas with no right answer - only 
different levels of suckiness.

Constraining "the system" to always loads drivers in a specific order, and 
hence not randomly rename interfaces at boot time is wrong.

Using stupidly long/complicated device names based on physical location is 
wrong. Doubly wrong when location can be highly variable (as in USB devices)*

Using stupidly long/complicated device names incorporating the device serial 
number (or MAC) is wrong.

Using persistent rules files (as with Udev) is wrong.

However, I am happy with the way Udev does it. Booting a "new" system results 
in an initially random device ordering, but once it's created a rules file the 
devices stay stable until "something changes". When changing hardware, or 
shifting the image to new hardware, new devices get created and the admin needs 
to "fix" it - but TBH it's not hard to do.
IMO - the sort of person who cannot edit the system created rules file is also 
not likely to be running the sort of system where it matters. Eg, they are 
likely to be the sort of use who plugs a cable into a hole in the back of the 
computer, and "the system" takes care of enabling it and getting addresses via 
DHCP/autoconf - the user doesn't care if it's eth0, eth57, flurbleport29, or 
anything else as long as "the network works". If for some reason they replace a 
network card, it's not likely to matter to them that eth0 is now called eth1 - 
as long as "it just works".

I don't tend to use ethn anyway on bare metal systems - they all have Udev 
rules to set meaningful names like ethext, ethlan, ethint, and so on. Different 
on my Xen VMs (Debian [Sarge** ... Wheezy] as out of the box there doesn't seem 
to be a Udev rules file created and it's never bugged me enough to figure out 
why !

* I've only hearsay evidence from the screams of colleagues, but it seems that 
some Windows stuff (in this context, setting up automated backups) is sensitive 
to which port the disk is plugged into. As in, if the user plugs the backup 
disk into the wrong USB port, it gets a different drive letter (how 20th 
century !) and the backup (which uses drive letter and not anything more 
sensible) fails.

** Yup. still got one of those running !


There is something of a parallel with filesystems/disks - where the results of 
"getting it wrong" are more significant. I recall back when I had "a bit less 
experience" and the problem was fairly new, having issues with a system where 
disks came up in random order during boot (two different controllers). Now I 
generally use disk (filesystem) labels - though it's "annoying" that Debian 
doesn't support filesystem labels for Grub - which have the advantage of having 
their own persistent storage attached to the device, but the same problems when 
moving things around.
It certainly needs a little care when identifying disks/filesystems by label in 
Xen VM configs.

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Re: [DNG] Purpose of an OS: was network device naming (was: What can I do after netman?)

[Timo Buhrmester]

> > The whole point of having 'an operating system'
> > is that it provides an abstract interface userspace software can use
> > to interact with the physical components of a different computer
> > according to the functions they're supposed to be provide, regardless
> > of the way this particular computer happens to be assembled.
> 
> Does anyone else agree with me that in the preceding sentence Rainer
> encapsulated the entire philosophy of people desiring simple and
> logical software? Rainer, can I quote your preceding sentence elsewhere?

Sounds more like a (rather accurate) explanation on what's the point
of an OS to me.  See Windows for an implementation of this idea that
does not rely on simple and logical software, so, IMO that isn't
implicit to what you quoted.


> > Considering this, encoding details of the bus layout and current bus
> > configuration in network interface names is just profoundly stupid.
> 
> I thought it was stupid for other reasons, but now that you mention it,
> yeah, naming it after the particular slot into which it's plugged in is
> stupid, and if you take the box apart and move things around, you can
> break your OS.

Couldn't agree more.
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