Re: [PATCH v5] net: ip, diag -- Add diag interface for raw sockets

On Wed, 2016-09-28 at 14:27 +0300, Cyrill Gorcunov wrote:

On Wed, Sep 28, 2016 at 07:06:26AM -0400, Jamal Hadi Salim wrote:

quoted

quoted

This structure is uapi, so anyone has complete rights to reference
@pad in the userspace programs. Sure it would be more clear to remove
the @pad completely, but if we choose so I think it's better to do
on top instead and then if someone complain we can easily revert
the single trivial commit instead of this big patch.

I am conflicted.
A field labelled "pad" does not appear to be valid as "UAPI". It is
a cosmetic indicator. If you did sizeof() with or without it being
present the value doesnt change.

I think you miss the point what I'm trying to say: currently end-user
may have reference to this member (for any reason) and his program
will compile and run. If we change the name the compilation procedure
fails and this will break API. Yes, referrning @pad is bad idea for
userspace code, and yes (!) better to simply rename it but lets do
that later, on top, so that if we break something in userspace
we could easily revert the oneline change.

Note that some programs could fail to compile with the added union
anyway.

Some gcc versions are unable to compile a static init with an union

struct inet_diag_req_v2 foo = { .pad = 0, sdiag_family = AF_INET, };

When I cooked my recent fq commit I simply removed a pad and replaced
it :

git show fefa569a9d4bc4 -- include