[Buildroot] Question on udhcpc script

[Buildroot] Question on udhcpc script

[Bhattiprolu RaviKumar]

 All,
  We are using busybox to get DHCPv6  address. However, I am bit confused
on the part of the script /etc/udhcpc.d/50default:

wait_for_ipv6_default_route() {
*        printf "Waiting for IPv6 default route to appear"*
        while [ $IF_WAIT_DELAY -gt 0 ]; do
*                if [ -z "$(ip -6 route list | grep default)" ]; then*
                        printf "\n"
                        return
                fi
                sleep 1
                printf "."
                : $((IF_WAIT_DELAY -= 1))
        done
        printf " timeout!\n"
}

The print says "Waiting for IPv6 default route to appear". However the if
statement is checking for "$(ip -6 route list | grep default)"to be null
(-z check) which means default route is not present.

In our case, after DHCP, default route gets setup and "$(ip -6 route list |
grep default)"returns an entry starting with default and since check is -z,
it continues in the loop and finally prints "timeout".

I am confused here. Am I missing something here?
regards,
Ravi
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[Buildroot] Question on udhcpc script

[Peter Korsgaard]

>>>>> "Bhattiprolu" == Bhattiprolu RaviKumar <ravikumar.bhattiprolu@gmail.com> writes:

 >  All,
 >   We are using busybox to get DHCPv6  address. However, I am bit confused
 > on the part of the script /etc/udhcpc.d/50default:

We don't have have such a script in Buildroot? It looks like yocto does
though:

https://git.yoctoproject.org/cgit.cgi/poky/commit/?id=763b11d0fd6b804c73f0f645a3025c8f82f5aaf1&context=6

Please direct yocto questions to yocto.

-- 
Bye, Peter Korsgaard

[Buildroot] Question on udhcpc script

[Bhattiprolu RaviKumar]

Peter,
  The script in yocto seems to be derived from
package/busybox/udhcpc.script in buildroot. It also had the same
"wait_for_ipv6_default_route" function and same check.
regards,
Ravi

On Mon, Feb 1, 2021 at 5:54 PM Peter Korsgaard <peter@korsgaard.com> wrote:

> >>>>> "Bhattiprolu" == Bhattiprolu RaviKumar <
> ravikumar.bhattiprolu at gmail.com> writes:
>
>  >  All,
>  >   We are using busybox to get DHCPv6  address. However, I am bit
> confused
>  > on the part of the script /etc/udhcpc.d/50default:
>
> We don't have have such a script in Buildroot? It looks like yocto does
> though:
>
>
> https://git.yoctoproject.org/cgit.cgi/poky/commit/?id=763b11d0fd6b804c73f0f645a3025c8f82f5aaf1&context=6
>
> Please direct yocto questions to yocto.
>
> --
> Bye, Peter Korsgaard
>
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[Buildroot] Question on udhcpc script

[Peter Korsgaard]

>>>>> "Bhattiprolu" == Bhattiprolu RaviKumar <ravikumar.bhattiprolu@gmail.com> writes:

 > Peter,

 >  All,
 >   We are using busybox to get DHCPv6  address. However, I am bit confused
 > on the part of the script /etc/udhcpc.d/50default:

 > wait_for_ipv6_default_route() {
 > *        printf "Waiting for IPv6 default route to appear"*
 >         while [ $IF_WAIT_DELAY -gt 0 ]; do
 > *                if [ -z "$(ip -6 route list | grep default)" ]; then*
 >                         printf "\n"
 >                         return
 >                 fi
 >                 sleep 1
 >                 printf "."
 >                 : $((IF_WAIT_DELAY -= 1))
 >         done
 >         printf " timeout!\n"
 > }

 > The print says "Waiting for IPv6 default route to appear". However the if
 > statement is checking for "$(ip -6 route list | grep default)"to be null
 > (-z check) which means default route is not present.

 > In our case, after DHCP, default route gets setup and "$(ip -6 route list |
 > grep default)"returns an entry starting with default and since check is -z,
 > it continues in the loop and finally prints "timeout".

 > I am confused here. Am I missing something here?

 >   The script in yocto seems to be derived from
 > package/busybox/udhcpc.script in buildroot. It also had the same
 > "wait_for_ipv6_default_route" function and same check.

Ok, but please be specific when you ask questions. So your question is
really about the code in package/busybox/udhcpc.script which got added
by:

commit 2d458a2d7c7f3418242aae52464306ef9f4a407f
Author: Samuel Mendoza-Jonas <sam@mendozajonas.com>
Date:   Tue May 21 12:54:28 2019 +1000

   package/busybox: udhcpc.script: wait for ipv6 default route from RA for stateful DHCPv6

   udhcpc6 implements "stateful" DHCPv6 for explicitly requesting an address
   and other configuration information. A major difference between DHCPv4
   and DHCPv6 is that DHCPv6 does *not* advertise a default route; this is
   determined by normal IPv6 autoconfiguration.

   Add logic to wait up to IF_WAIT_DELAY seconds for the IPv6 route to be
   configured; as above this doesn't come from DHCPv6 but rather the IPv6
   Router Advertisement (RA) which happens independently from udhcpc6.  The
   intent here is to try and ensure that the interface is route-able upon the
   script's completion as it would be if called from udhcpc.

   Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
   Signed-off-by: Peter Korsgaard <peter@korsgaard.com>


The test indeed seems to be inverted. Samuel, any comments?

-- 
Bye, Peter Korsgaard

[Buildroot] Question on udhcpc script

[Samuel Mendoza-Jonas]

On Mon, 2021-02-01 at 14:56 +0100, Peter Korsgaard wrote:
> > > > > 
> The test indeed seems to be inverted. Samuel, any comments?

Only that I'm curious to know how this happened! I agree, that logic
looks inverted, the line could be simplified to something like

diff --git a/package/busybox/udhcpc.script
b/package/busybox/udhcpc.script
index ec4d9f6185..c73ad6c2ef 100755
--- a/package/busybox/udhcpc.script
+++ b/package/busybox/udhcpc.script
@@ -18,7 +18,7 @@ fi
 wait_for_ipv6_default_route() {
        printf "Waiting for IPv6 default route to appear"
        while [ $IF_WAIT_DELAY -gt 0 ]; do
-               if [ -z "$(ip -6 route list | grep default)" ]; then
+               if ip -6 route list | grep -q default; then
                        printf "\n"
                        return
                fi

I can send a quick proper patch if you'd like.

Sam

[Buildroot] Question on udhcpc script

[Samuel Mendoza-Jonas]

On Mon, 2021-02-01 at 17:33 -0800, Samuel Mendoza-Jonas wrote:
> On Mon, 2021-02-01 at 14:56 +0100, Peter Korsgaard wrote:
> > > > > > 
> > The test indeed seems to be inverted. Samuel, any comments?
> 
> Only that I'm curious to know how this happened! I agree, that logic
> looks inverted, the line could be simplified to something like
> 
> diff --git a/package/busybox/udhcpc.script
> b/package/busybox/udhcpc.script
> index ec4d9f6185..c73ad6c2ef 100755
> --- a/package/busybox/udhcpc.script
> +++ b/package/busybox/udhcpc.script
> @@ -18,7 +18,7 @@ fi
> ?wait_for_ipv6_default_route() {
> ??????? printf "Waiting for IPv6 default route to appear"
> ??????? while [ $IF_WAIT_DELAY -gt 0 ]; do
> -?????????????? if [ -z "$(ip -6 route list | grep default)" ]; then
> +?????????????? if ip -6 route list | grep -q default; then
> ??????????????????????? printf "\n"
> ??????????????????????? return
> ??????????????? fi
> 
> I can send a quick proper patch if you'd like.
> 
> Sam

In fact, here we go:
https://patchwork.ozlabs.org/project/buildroot/patch/20210202015452.98002-1-sam at mendozajonas.com/

[Buildroot] Question on udhcpc script

[Bhattiprolu RaviKumar]

Thanks Sam,Peter for quick closure.
regards,
Ravi

On Tue, Feb 2, 2021 at 7:26 AM Samuel Mendoza-Jonas <sam@mendozajonas.com>
wrote:

> On Mon, 2021-02-01 at 17:33 -0800, Samuel Mendoza-Jonas wrote:
> > On Mon, 2021-02-01 at 14:56 +0100, Peter Korsgaard wrote:
> > > > > > >
> > > The test indeed seems to be inverted. Samuel, any comments?
> >
> > Only that I'm curious to know how this happened! I agree, that logic
> > looks inverted, the line could be simplified to something like
> >
> > diff --git a/package/busybox/udhcpc.script
> > b/package/busybox/udhcpc.script
> > index ec4d9f6185..c73ad6c2ef 100755
> > --- a/package/busybox/udhcpc.script
> > +++ b/package/busybox/udhcpc.script
> > @@ -18,7 +18,7 @@ fi
> >  wait_for_ipv6_default_route() {
> >         printf "Waiting for IPv6 default route to appear"
> >         while [ $IF_WAIT_DELAY -gt 0 ]; do
> > -               if [ -z "$(ip -6 route list | grep default)" ]; then
> > +               if ip -6 route list | grep -q default; then
> >                         printf "\n"
> >                         return
> >                 fi
> >
> > I can send a quick proper patch if you'd like.
> >
> > Sam
>
> In fact, here we go:
>
> https://patchwork.ozlabs.org/project/buildroot/patch/20210202015452.98002-1-sam at mendozajonas.com/
>
>
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