netdev - Re: [PATCH iproute2-next v3 5/8] veth,vxcan: Save/reinitialize/restore whole @struct ifinfomsg

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Message-ID: <0a97556a-d678-21d4-e028-35077b317a71@gmail.com>
Date:   Mon, 26 Feb 2018 17:48:16 +0200
From:   Serhey Popovych <serhe.popovych@...il.com>
To:     David Ahern <dsahern@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH iproute2-next v3 5/8] veth,vxcan:
 Save/reinitialize/restore whole @struct ifinfomsg

David Ahern wrote:
> On 2/22/18 6:02 AM, Serhey Popovych wrote:
>> Now in iplink_parse() we use ->ifi_change and ->ifi_flags fields and
>> plan to use ->ifi_index with upcoming change.
>>
>> Saving, restoring and reinitializing individual fields is error prone:
>> using new field in iplink_parse() without updating callers in veth and
>> vxcan will overwrite main device ifinfomsg data.
>>
>> Since @struct ifinfomsg is small enough with known sizeof() compiler may
>> inline memcpy()/memset() with few load/store instructions.
>>
>> Signed-off-by: Serhey Popovych <serhe.popovych@...il.com>
>> ---
>>  ip/iplink_vxcan.c |   22 ++++++++--------------
>>  ip/link_veth.c    |   22 ++++++++--------------
>>  2 files changed, 16 insertions(+), 28 deletions(-)
> 
> I don't agree that this change has any benefit. Only the flags and
> change field are wanted; there is no need to save the entire struct,
> 

Struct is small enough, only ifi_change and ifi_flags being used right
now, but next patch also changes ifi_index. Remaining values are fit in
single u32 (ifi_family, ifi_type and pad). So we copy only one extra u32
at the moment. Later if something gets changed and iplink_parse() starts
using ifi_family, ifi_type, ifi_pad... we do not need to modify vxcan
and veth modules.



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