Re: [PATCH] Allow userspace code to use flag IFA_F_SECONDARY tospecify an ip address to be primary or secondary ip on an interface

[Vincent Li]

Thanks Julian for the comments, I imagined it would not be so simple
as it changed old behavior with ip binary and some actions in
__inet_del_ifa() that I am not fully aware of. my intention is to
preserve the old behavior and extend the flexibility, I am unable to
come up with a good patch to achieve the intended behavior.

I had to patch the ip binary to sort of preserve original ip binary
behavior with the kernel patch I provided., the ip command patch
below:

diff --git a/ip/ipaddress.c b/ip/ipaddress.c
index 1c3e4da..9f2802c 100644
--- a/ip/ipaddress.c
+++ b/ip/ipaddress.c
@@ -1259,6 +1259,7 @@ static int ipaddr_modify(int cmd, int flags, int
argc, char **argv)
        req.n.nlmsg_flags = NLM_F_REQUEST | flags;
        req.n.nlmsg_type = cmd;
        req.ifa.ifa_family = preferred_family;
+       req.ifa.ifa_flags |= IFA_F_SECONDARY;

        while (argc > 0) {
                if (strcmp(*argv, "peer") == 0 ||
@@ -1307,6 +1308,11 @@ static int ipaddr_modify(int cmd, int flags,
int argc, char **argv)
                                invarg("invalid scope value.", *argv);
                        req.ifa.ifa_scope = scope;
                        scoped = 1;
+                } else if (strcmp(*argv, "secondary") == 0 ||
+                           strcmp(*argv, "temporary") == 0) {
+                        req.ifa.ifa_flags |= IFA_F_SECONDARY;
+                } else if (strcmp(*argv, "primary") == 0) {
+                        req.ifa.ifa_flags &= ~IFA_F_SECONDARY;
                } else if (strcmp(*argv, "dev") == 0) {
                        NEXT_ARG();
                        d = *argv;

if someone can point me to the right patch directions or coming up
with better patches, it is very much appreciated.


On Tue, Sep 24, 2013 at 2:13 PM, Julian Anastasov <ja@xxxxxx> wrote:
>
>         Hello,
>
> On Tue, 24 Sep 2013, Vincent Li wrote:
>
>> the current behavior is when an IP is added to an interface, the primary
>> or secondary attributes is depending on the order of ip added to the interface
>> the first IP will be primary and second, third,... or alias IP will be secondary
>> if the IP subnet matches
>>
>> this patch add the flexiblity to allow user to specify an argument 'primary' or 'secondary'
>> (use 'ip addr add ip/mask primary|secondary dev ethX ' from iproute2 for example) to specify
>> an IP address to be  primary or secondary.
>>
>> the reason for this patch is that we have a multi blade cluster platform sharing 'floating management ip'
>> and also that each blade has its own management ip on the management interface, so whichever blade in the
>> cluster becomes primary blade, the 'floating mangaement ip' follows it, and we want any of our traffic
>> originated from the primary blade source from the 'floating management ip' for consistency. but in this
>> case, since the local blade management ip is always the primary ip on the mangaement interface and 'floating
>> management ip' is always secondary, kernel always choose the primary ip as source ip address. thus we would
>> like to add the flexibility in kernel to allow us to specify which ip to be primary or secondary.
>>
>> Signed-off-by: Vincent Li <vincent.mc.li@xxxxxxxxx>
>> ---
>>  net/ipv4/devinet.c |    9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
>> index a1b5bcb..bfc702a 100644
>> --- a/net/ipv4/devinet.c
>> +++ b/net/ipv4/devinet.c
>> @@ -440,9 +440,11 @@ static int __inet_insert_ifa(struct in_ifaddr *ifa, struct nlmsghdr *nlh,
>>               return 0;
>>       }
>>
>> -     ifa->ifa_flags &= ~IFA_F_SECONDARY;
>>       last_primary = &in_dev->ifa_list;
>>
>> +     if((*last_primary) == NULL)
>> +             ifa->ifa_flags &= ~IFA_F_SECONDARY;
>> +
>>       for (ifap = &in_dev->ifa_list; (ifa1 = *ifap) != NULL;
>>            ifap = &ifa1->ifa_next) {
>>               if (!(ifa1->ifa_flags & IFA_F_SECONDARY) &&
>> @@ -458,7 +460,10 @@ static int __inet_insert_ifa(struct in_ifaddr *ifa, struct nlmsghdr *nlh,
>>                               inet_free_ifa(ifa);
>>                               return -EINVAL;
>>                       }
>> -                     ifa->ifa_flags |= IFA_F_SECONDARY;
>
>         There is some confusion here, when ifa has
> IFA_F_SECONDARY bit set, in the 'else' we set it again.
> I guess the 'else' part is not needed.
>
>> +                        if (!(ifa->ifa_flags & IFA_F_SECONDARY))
>> +                                ifa1->ifa_flags |= IFA_F_SECONDARY;
>> +                        else
>> +                                ifa->ifa_flags |= IFA_F_SECONDARY;
>
>         It should not be so simple. You can not
> just change the flag of existing address (ifa1) to secondary.
> See __inet_del_ifa(), there are many more actions that
> follow:
>
> - kernel routes that use this primary address
> should be deleted and recreated with the new primary
> address as source. This includes local routes to secondary
> IPs.
>
> - RTM_NEWADDR should be sent, so that user space see
> the IFA_F_SECONDARY flag
>
>         Some questions:
>
> - should we allow adding of secondary IPs when no primary
> address exists for the subnet, it can happen when primary
> for another subnet already exists
>
> - by default, existing 'ip addr' binaries will provide
> address without IFA_F_SECONDARY flag. Before now we added
> such addresses as last for the subnet, now the
> behaviour changes, we start to add addresses in reverse
> order. Is that true? I.e. before now the operation was
> APPEND, now we need a way to provide PREPEND operation.
>
> Regards
>
> --
> Julian Anastasov <ja@xxxxxx>
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