netdev - Re: [Intel-wired-lan] [PATCH bpf-next v4 03/11] libbpf: add flags to umem config

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Date:   Thu, 1 Aug 2019 09:34:47 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Kevin Laatz <kevin.laatz@...el.com>,
        Netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Maxim Mikityanskiy <maximmi@...lanox.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Bruce Richardson <bruce.richardson@...el.com>,
        ciara.loftus@...el.com,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [Intel-wired-lan] [PATCH bpf-next v4 03/11] libbpf: add flags to
 umem config

On Thu, 1 Aug 2019 at 08:59, Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
>
> On Wed, Jul 31, 2019 at 8:21 AM Björn Töpel <bjorn.topel@...il.com> wrote:
> >
> > On Tue, 30 Jul 2019 at 19:43, Kevin Laatz <kevin.laatz@...el.com> wrote:
> > >
> > > This patch adds a 'flags' field to the umem_config and umem_reg structs.
> > > This will allow for more options to be added for configuring umems.
> > >
> > > The first use for the flags field is to add a flag for unaligned chunks
> > > mode. These flags can either be user-provided or filled with a default.
> > >
> > > Signed-off-by: Kevin Laatz <kevin.laatz@...el.com>
> > > Signed-off-by: Ciara Loftus <ciara.loftus@...el.com>
> > >
> > > ---
> > > v2:
> > >   - Removed the headroom check from this patch. It has moved to the
> > >     previous patch.
> > >
> > > v4:
> > >   - modified chunk flag define
> > > ---
>
> [...]
>
> > > diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
> > > index 833a6e60d065..44a03d8c34b9 100644
> > > --- a/tools/lib/bpf/xsk.h
> > > +++ b/tools/lib/bpf/xsk.h
> > > @@ -170,12 +170,14 @@ LIBBPF_API int xsk_socket__fd(const struct xsk_socket *xsk);
> > >  #define XSK_UMEM__DEFAULT_FRAME_SHIFT    12 /* 4096 bytes */
> > >  #define XSK_UMEM__DEFAULT_FRAME_SIZE     (1 << XSK_UMEM__DEFAULT_FRAME_SHIFT)
> > >  #define XSK_UMEM__DEFAULT_FRAME_HEADROOM 0
> > > +#define XSK_UMEM__DEFAULT_FLAGS 0
> > >
> > >  struct xsk_umem_config {
> > >         __u32 fill_size;
> > >         __u32 comp_size;
> > >         __u32 frame_size;
> > >         __u32 frame_headroom;
> > > +       __u32 flags;
> >
> > And the flags addition here, unfortunately, requires symbol versioning
> > of xsk_umem__create(). That'll be the first in libbpf! :-)
>
> xsk_umem_config is passed by pointer to xsk_umem__create(), so this
> doesn't break ABI, does it?
>

Old application, dynamically linked to new libbpf.so will crash,
right? Old application passes old version of xsk_umem_config, and new
library accesses (non-existing) flag struct member.

Björn

> >
> >
> > Björn
> >
> > >  };
> > >
> > >  /* Flags for the libbpf_flags field. */
> > > --
> > > 2.17.1
> > >
> > > _______________________________________________
> > > Intel-wired-lan mailing list
> > > Intel-wired-lan@...osl.org
> > > https://lists.osuosl.org/mailman/listinfo/intel-wired-lan

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