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SubjectRe: [PATCH v3 net-next] net: drop_monitor: support drop reason
On Thu, Jan 27, 2022 at 08:53:04AM -0700, David Ahern wrote:
> On 1/26/22 8:33 PM, menglong8.dong@gmail.com wrote:
> > From: Menglong Dong <imagedong@tencent.com>
> >
> > In the commit c504e5c2f964 ("net: skb: introduce kfree_skb_reason()")
> > drop reason is introduced to the tracepoint of kfree_skb. Therefore,
> > drop_monitor is able to report the drop reason to users by netlink.
> >
> > For now, the number of drop reason is passed to users ( seems it's
> > a little troublesome to pass the drop reason as string ). Therefore,
> > users can do some customized description of the reason.
> >
> > Signed-off-by: Menglong Dong <imagedong@tencent.com>
> > ---
> > v3:
> > - referring to cb->reason and cb->pc directly in
> > net_dm_packet_report_fill()
> >
> > v2:
> > - get a pointer to struct net_dm_skb_cb instead of local var for
> > each field
> > ---
> > include/uapi/linux/net_dropmon.h | 1 +
> > net/core/drop_monitor.c | 16 ++++++++++++----
> > 2 files changed, 13 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/uapi/linux/net_dropmon.h b/include/uapi/linux/net_dropmon.h
> > index 66048cc5d7b3..b2815166dbc2 100644
> > --- a/include/uapi/linux/net_dropmon.h
> > +++ b/include/uapi/linux/net_dropmon.h
> > @@ -93,6 +93,7 @@ enum net_dm_attr {
> > NET_DM_ATTR_SW_DROPS, /* flag */
> > NET_DM_ATTR_HW_DROPS, /* flag */
> > NET_DM_ATTR_FLOW_ACTION_COOKIE, /* binary */
> > + NET_DM_ATTR_REASON, /* u32 */
> >
>
> For userspace to properly convert reason from id to string, enum
> skb_drop_reason needs to be moved from skbuff.h to a uapi file.
> include/uapi/linux/net_dropmon.h seems like the best candidate to me.
> Maybe others have a better idea.

I think the best option would be to convert it to a string in the kernel
(or report both). Then you don't need to update user space tools such as
the Wireshark dissector [1] and DropWatch every time a new reason is
added.

[1] https://www.wireshark.org/docs/dfref/n/net_dm.html

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