download_dev-random hook question

download_dev-random hook question

[Christian Storm]

Hi,

I just stumbled over the download_dev-random multistrap hook:
Why is it that you only create /dev/{,u}random?
Why not also create other essential files like /dev/{null,zero}
as well, e.g., like this:

```
--- a/meta/recipes-devtools/buildchroot/files/download_dev-random
+++ b/meta/recipes-devtools/buildchroot/files/download_dev-random
@@ -4,10 +4,14 @@ set -e
 
 readonly ROOTFS="$1"
 
-mknod "${ROOTFS}/dev/random" c 1 8
-chmod 640 "${ROOTFS}/dev/random"
+mknod -m 640 "${ROOTFS}/dev/random" c 1 8
 chown 0:0 "${ROOTFS}/dev/random"
 
-mknod "${ROOTFS}/dev/urandom" c 1 9
-chmod 640 "${ROOTFS}/dev/urandom"
+mknod -m 640 "${ROOTFS}/dev/urandom" c 1 9
 chown 0:0 "${ROOTFS}/dev/urandom"
+
+mknod -m 666 "${ROOTFS}/dev/null" c 1 3
+chown 0:0 "${ROOTFS}/dev/null"
+
+mknod -m 666 "${ROOTFS}/dev/zero" c 1 5
+chown 0:0 "${ROOTFS}/dev/zero"
```



Besten Gru�,
   Christian

-- 
Dr. Christian Storm
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Otto-Hahn-Ring 6, 81739 M�nchen, Germany

Re: download_dev-random hook question

[Henning Schild]

Good question, looking at the commit it does not become clear. Putting
the author on CC.

Christian, you patched it to shrink it. Did you try removing that step?
I can just guess that nodes will be created by packages/hooks and
something in multistrap needs certain nodes before that happens.


Henning

Am Mon, 13 Nov 2017 17:35:46 +0100
schrieb "[ext] Christian Storm" <christian.storm@siemens.com>:

> Hi,
> 
> I just stumbled over the download_dev-random multistrap hook:
> Why is it that you only create /dev/{,u}random?
> Why not also create other essential files like /dev/{null,zero}
> as well, e.g., like this:
> 
> ```
> --- a/meta/recipes-devtools/buildchroot/files/download_dev-random
> +++ b/meta/recipes-devtools/buildchroot/files/download_dev-random
> @@ -4,10 +4,14 @@ set -e
>  
>  readonly ROOTFS="$1"
>  
> -mknod "${ROOTFS}/dev/random" c 1 8
> -chmod 640 "${ROOTFS}/dev/random"
> +mknod -m 640 "${ROOTFS}/dev/random" c 1 8
>  chown 0:0 "${ROOTFS}/dev/random"
>  
> -mknod "${ROOTFS}/dev/urandom" c 1 9
> -chmod 640 "${ROOTFS}/dev/urandom"
> +mknod -m 640 "${ROOTFS}/dev/urandom" c 1 9
>  chown 0:0 "${ROOTFS}/dev/urandom"
> +
> +mknod -m 666 "${ROOTFS}/dev/null" c 1 3
> +chown 0:0 "${ROOTFS}/dev/null"
> +
> +mknod -m 666 "${ROOTFS}/dev/zero" c 1 5
> +chown 0:0 "${ROOTFS}/dev/zero"
> ```
> 
> 
> 
> Besten Gruß,
>    Christian
> 

Re: download_dev-random hook question

[[ext] Christian Storm]

> [...]
> Christian, you patched it to shrink it. Did you try removing that step?

Nope, and I'd like to extend that step in terms of /dev/ nodes to be
created instead of removing it :)

> I can just guess that nodes will be created by packages/hooks and
> something in multistrap needs certain nodes before that happens.

Yes, a subset of the standard ones (TM) are required, i.e.,
/dev/{null,{u,}random,...}, you name it.

So, I'd like to have a static /dev/ setup in such a way that the
essential files required to boot are present, even without udev or the
like having created them dynamically.
To be precise, I'd like a to-be-renamed download_dev-random to include
  mknod -m 666 /dev/null c 1 3
  mknod -m 666 /dev/zero c 1 5
  mknod -m 666 /dev/random c 1 8
  mknod -m 666 /dev/urandom c 1 9
  mkdir -m 755 /dev/pts
  mkdir -m 1777 /dev/shm
  mknod -m 666 /dev/tty c 5 0
  mknod -m 600 /dev/console c 5 1
  mknod -m 666 /dev/tty0 c 4 0
  mknod -m 666 /dev/full c 1 7
  mknod -m 600 /dev/initctl p
  mknod -m 666 /dev/ptmx c 5 2


Besten Gru�,
   Christian

-- 
Dr. Christian Storm
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Otto-Hahn-Ring 6, 81739 M�nchen, Germany

Re: download_dev-random hook question

[[ext] Christian Storm]

> I just stumbled over the download_dev-random multistrap hook:
> Why is it that you only create /dev/{,u}random?
> Why not also create other essential files like /dev/{null,zero}
> as well [...]

... and, a further question that just came to my mind: Why is this handled
in a multistrap hook in the first place? Seems rather implicit to me. Why 
not do it explicitly in buildchroot.bb and isar-image-base.bb?


Besten Gru�,
   Christian

-- 
Dr. Christian Storm
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Otto-Hahn-Ring 6, 81739 M�nchen, Germany

Re: download_dev-random hook question

[Alexander Smirnov]

Hi,

On 11/16/2017 12:04 PM, [ext] Christian Storm wrote:
>> I just stumbled over the download_dev-random multistrap hook:
>> Why is it that you only create /dev/{,u}random?
>> Why not also create other essential files like /dev/{null,zero}
>> as well [...]
> 
> ... and, a further question that just came to my mind: Why is this handled
> in a multistrap hook in the first place? Seems rather implicit to me. Why
> not do it explicitly in buildchroot.bb and isar-image-base.bb?
>

IIRC correctly multistrap configuration was taken from Debian/Embian 
examples. So I'd personally prefer to drop all the hooks and make 
necessary calls explicitly in recipes.

So I see it like the following:
  - recipe creates rootfs, mounts necessary folders and creates device 
files.
  - recipe calls multistrap which only downloads the packages and unpack 
them to rootfs.
  - recipe calls configscript which performs post-configuration for rootfs.

This would be very helpful in context of switching to debootstrap.

Alex

Re: download_dev-random hook question

[Christian Storm]

> >> I just stumbled over the download_dev-random multistrap hook:
> >> Why is it that you only create /dev/{,u}random?
> >> Why not also create other essential files like /dev/{null,zero}
> >> as well [...]
> > 
> > ... and, a further question that just came to my mind: Why is this handled
> > in a multistrap hook in the first place? Seems rather implicit to me. Why
> > not do it explicitly in buildchroot.bb and isar-image-base.bb?
> >
> 
> IIRC correctly multistrap configuration was taken from Debian/Embian 
> examples. So I'd personally prefer to drop all the hooks and make 
> necessary calls explicitly in recipes.

Ah, I see... I totally agree.

> So I see it like the following:
>   - recipe creates rootfs, mounts necessary folders and creates device files.
>   - recipe calls multistrap which only downloads the packages and unpack 
>     them to rootfs.
>   - recipe calls configscript which performs post-configuration for rootfs.

Yes, we're on the same page here, agreed.

> This would be very helpful in context of switching to debootstrap.

Even without the switch, I do find the explicit variant, well, more explicit :)


Besten Gru�,
   Christian

-- 
Dr. Christian Storm
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Otto-Hahn-Ring 6, 81739 M�nchen, Germany

Re: download_dev-random hook question

[Alexander Smirnov]

Hi,

On 11/16/2017 12:41 PM, Christian Storm wrote:
>>>> I just stumbled over the download_dev-random multistrap hook:
>>>> Why is it that you only create /dev/{,u}random?
>>>> Why not also create other essential files like /dev/{null,zero}
>>>> as well [...]
>>>
>>> ... and, a further question that just came to my mind: Why is this handled
>>> in a multistrap hook in the first place? Seems rather implicit to me. Why
>>> not do it explicitly in buildchroot.bb and isar-image-base.bb?
>>>
>>
>> IIRC correctly multistrap configuration was taken from Debian/Embian
>> examples. So I'd personally prefer to drop all the hooks and make
>> necessary calls explicitly in recipes.
> 
> Ah, I see... I totally agree.
> 
>> So I see it like the following:
>>    - recipe creates rootfs, mounts necessary folders and creates device files.
>>    - recipe calls multistrap which only downloads the packages and unpack
>>      them to rootfs.
>>    - recipe calls configscript which performs post-configuration for rootfs.
> 
> Yes, we're on the same page here, agreed.
> 
>> This would be very helpful in context of switching to debootstrap.
> 
> Even without the switch, I do find the explicit variant, well, more explicit :)
> 

Will you handle this? :-) Or I could add it to TODO?

Alex

Re: download_dev-random hook question

[Christian Storm]

> >>>> I just stumbled over the download_dev-random multistrap hook:
> >>>> Why is it that you only create /dev/{,u}random?
> >>>> Why not also create other essential files like /dev/{null,zero}
> >>>> as well [...]
> >>>
> >>> ... and, a further question that just came to my mind: Why is this handled
> >>> in a multistrap hook in the first place? Seems rather implicit to me. Why
> >>> not do it explicitly in buildchroot.bb and isar-image-base.bb?
> >>>
> >>
> >> IIRC correctly multistrap configuration was taken from Debian/Embian
> >> examples. So I'd personally prefer to drop all the hooks and make
> >> necessary calls explicitly in recipes.
> > 
> > Ah, I see... I totally agree.
> > 
> >> So I see it like the following:
> >>    - recipe creates rootfs, mounts necessary folders and creates device files.
> >>    - recipe calls multistrap which only downloads the packages and unpack
> >>      them to rootfs.
> >>    - recipe calls configscript which performs post-configuration for rootfs.
> > 
> > Yes, we're on the same page here, agreed.
> > 
> >> This would be very helpful in context of switching to debootstrap.
> > 
> > Even without the switch, I do find the explicit variant, well, more explicit :)
> > 
> 
> Will you handle this? :-) Or I could add it to TODO?

It fell on my feet, so I'll prepare patches, stay tuned...



Besten Gru�,
   Christian

-- 
Dr. Christian Storm
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Otto-Hahn-Ring 6, 81739 M�nchen, Germany

Re: download_dev-random hook question

[Henning Schild]

Am Thu, 16 Nov 2017 10:04:53 +0100
schrieb "[ext] [ext] Christian Storm" <christian.storm@siemens.com>:

> > I just stumbled over the download_dev-random multistrap hook:
> > Why is it that you only create /dev/{,u}random?
> > Why not also create other essential files like /dev/{null,zero}
> > as well [...]  
> 
> ... and, a further question that just came to my mind: Why is this
> handled in a multistrap hook in the first place? Seems rather
> implicit to me. Why not do it explicitly in buildchroot.bb and
> isar-image-base.bb?

Is a hook not explicit? I do not get the point. Using a script outside
of do_build even allows for sharing between the two users. And these two
recipes should probably be deduplicated one day.

Henning

> 
> Besten Gruß,
>    Christian
> 

Re: download_dev-random hook question

[Christian Storm]

> > > I just stumbled over the download_dev-random multistrap hook:
> > > Why is it that you only create /dev/{,u}random?
> > > Why not also create other essential files like /dev/{null,zero}
> > > as well [...]  
> > 
> > ... and, a further question that just came to my mind: Why is this
> > handled in a multistrap hook in the first place? Seems rather
> > implicit to me. Why not do it explicitly in buildchroot.bb and
> > isar-image-base.bb?
> 
> Is a hook not explicit? I do not get the point. 

It depends :)

In my opinion it's not explicit as /dev node generation is kind of a
side-effect of running multistrap realized via its hooks. If multistrap
would have done it anyway without us placing the hook in there, fine.
But we're placing a hook script in multistrap that does the work -
which could as well be done in do_build(), there named explicitly as
/dev node generation. If I wanted to know how/where /dev node generation
is done, there's as of now one more indirection in terms of the
multistrap hook. That said, I'm not strongly opinionated on this as I
guess it's mostly a matter of taste though...


> Using a script outside of do_build even allows for sharing between the
> two users. 

Yes, but this is also true if this external script is called from within
the two do_builds, explicitly.


> And these two recipes should probably be deduplicated one day.

Yes, I agree but that's another issue...



   Christian

-- 
Dr. Christian Storm
Siemens AG, Corporate Technology, CT RDA ITP SES-DE
Otto-Hahn-Ring 6, 81739 M�nchen, Germany