Re: [PATCH] net: qualcomm: rmnet: Allow partial updates of IFLA_FLAGS

[Alex Elder]

On 4/22/21 6:28 PM, subashab@xxxxxxxxxxxxxx wrote:
> On 2021-04-22 12:29, Alex Elder wrote:
> > On 4/22/21 1:20 PM, Bjorn Andersson wrote:
> > > The idiomatic way to handle the changelink flags/mask pair seems to be
> > > allow partial updates of the driver's link flags. In contrast the rmnet
> > > driver masks the incoming flags and then use that as the new flags.
> > >
> > > Change the rmnet driver to follow the common scheme, before the
> > > introduction of IFLA_RMNET_FLAGS handling in iproute2 et al.
> >
> > I like this a lot.  It should have been implemented this way
> > to begin with; there's not much point to have the mask if
> > it's only applied to the passed-in value.
> >
> > KS, are you aware of *any* existing user space code that
> > would not work correctly if this were accepted?
> >
> > I.e., the way it was (is), the value passed in *assigns*
> > the data format flags.  But with Bjorn's changes, the
> > data format flags would be *updated* (i.e., any bits not
> > set in the mask field would remain with their previous
> > value).
> >
> > Reviewed-by: Alex Elder <elder@xxxxxxxxxx>
>
> What rmnet functionality which was broken without this change.
> That doesnt seem to be listed in this patch commit text.

The broken functionality is that RMNet is not using the
value/flag pair in the proper way.

Currently, the RMNet driver assigns the flags value,
and (strangly) applies the mask to that value.

The intent of the value/flag pair interface is to allow
a value to be provided, with a mask of bits that indicate
which bits in the value should be *updated* in the target
field stored in the kernel.

That way, one can *assign* a value (by providing a value
with flag value 0xffffffff), but one can also update one
or any number of bits, preserving existing values.

It means, for example, that a request can preserve
existing settings, while *adding* a receive checksum
offload.

> If this is an enhancement, then patch needs to be targeted to net-next
> instead of net

Bjorn targeted neither net nor net-next.  He just posted
the patch.  I think it could be either.

					-Alex