Re: [PATCH net] net: enable interface alias removal via rtnl

On 10/9/17 9:25 AM, Nicolas Dichtel wrote:

Le 09/10/2017 à 16:02, David Ahern a écrit :

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On 10/9/17 2:23 AM, Nicolas Dichtel wrote:

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Le 06/10/2017 à 22:10, Oliver Hartkopp a écrit :

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On 10/06/2017 08:18 PM, David Ahern wrote:

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On 10/5/17 4:19 AM, Nicolas Dichtel wrote:

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IFLA_IFALIAS is defined as NLA_STRING. It means that the minimal length of
the attribute is 1 ("\0"). However, to remove an alias, the attribute
length must be 0 (see dev_set_alias()).

why not add a check in dev_set_alias that if len is 1 and the 1
character is '\0' it means remove the alias?

Because it requires an iproute2 patch. iproute2 doesn't send the '\0'. With the
command 'ip link set dummy0 alias ""', the attribute length is 0.

iproute2 needs the feature for 0-len strings or perhaps a 'noalias' option.

iproute2 needs nothing ...

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You can reset the alias using the sysfs file. Given that there is a
workaround for existing kernels and userspace, upstream can get fixed
without changing the UAPI.

I don't get the point with the UAPI. What will be broken?

never mind; I see the error of my ways.

I don't see why allowing an attribute with no data is a problem.

I remember the problem now. I made a patch back in March 2016 that
adjusted the policy validation to allow 0-length string. I never sent it
and forgot about it until today. You changing ifla_policy to NLA_BINARY
is achieving the same thing.

I think a comment above the policy line is warranted that clarifies
IFLA_IFALIAS is a string but to allow a 0-length string to remove the
alias NLA_BINARY is used for policy validation.

Comparing the validation done for NLA_STRING vs NLA_BINARY it does
change the behavior for 256-character strings.