netdev - Re: [PATCH v2 net-next 2/2] 6lowpan: Remove redundant initialisation.

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Date:   Tue, 28 Mar 2023 12:00:31 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     <mbloch@...dia.com>
CC:     <davem@...emloft.net>, <dsahern@...nel.org>, <edumazet@...gle.com>,
        <kuba@...nel.org>, <kuni1840@...il.com>, <kuniyu@...zon.com>,
        <netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH v2 net-next 2/2] 6lowpan: Remove redundant initialisation.

From:   Mark Bloch <mbloch@...dia.com>
Date:   Tue, 28 Mar 2023 09:27:43 +0300
> On 28/03/2023 2:54, Kuniyuki Iwashima wrote:
> > We'll call memset(&tmp, 0, sizeof(tmp)) later.
> 
> Why not just remove the first memset() then?

The same pattern (memset(), init, compare) is repeated twice, and
I thought it's cleaner.  I don't have no strong preference though.

Also, we need not init it if we hit 'goto out' in the first switch.

---8<---
static u8 lowpan_compress_ctx_addr(u8 **hc_ptr, const struct net_device *dev,
				   const struct in6_addr *ipaddr,
				   const struct lowpan_iphc_ctx *ctx,
				   const unsigned char *lladdr, bool sam)
{
	struct in6_addr tmp;
	u8 dam;

	switch (lowpan_dev(dev)->lltype) {
	case LOWPAN_LLTYPE_IEEE802154:
		if (lowpan_iphc_compress_ctx_802154_lladdr(ipaddr, ctx,
							   lladdr)) {
			dam = LOWPAN_IPHC_DAM_11;
			goto out;
		}
		break;
	default:
		if (lowpan_iphc_addr_equal(dev, ctx, ipaddr, lladdr)) {
			dam = LOWPAN_IPHC_DAM_11;
			goto out;
		}
		break;
	}

	memset(&tmp, 0, sizeof(tmp));
	/* check for SAM/DAM = 10 */
	tmp.s6_addr[11] = 0xFF;
	tmp.s6_addr[12] = 0xFE;
	memcpy(&tmp.s6_addr[14], &ipaddr->s6_addr[14], 2);
	/* context information are always used */
	ipv6_addr_prefix_copy(&tmp, &ctx->pfx, ctx->plen);
	if (ipv6_addr_equal(&tmp, ipaddr)) {
		lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr[14], 2);
		dam = LOWPAN_IPHC_DAM_10;
		goto out;
	}

	memset(&tmp, 0, sizeof(tmp));
	/* check for SAM/DAM = 01, should always match */
	memcpy(&tmp.s6_addr[8], &ipaddr->s6_addr[8], 8);
	/* context information are always used */
	ipv6_addr_prefix_copy(&tmp, &ctx->pfx, ctx->plen);
	if (ipv6_addr_equal(&tmp, ipaddr)) {
		lowpan_push_hc_data(hc_ptr, &ipaddr->s6_addr[8], 8);
		dam = LOWPAN_IPHC_DAM_01;
		goto out;
	}
...
}
---8<---


> 
> Mark
> 
> > 
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> > ---
> >  net/6lowpan/iphc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/6lowpan/iphc.c b/net/6lowpan/iphc.c
> > index 52fad5dad9f7..e116d308a8df 100644
> > --- a/net/6lowpan/iphc.c
> > +++ b/net/6lowpan/iphc.c
> > @@ -848,7 +848,7 @@ static u8 lowpan_compress_ctx_addr(u8 **hc_ptr, const struct net_device *dev,
> >  				   const struct lowpan_iphc_ctx *ctx,
> >  				   const unsigned char *lladdr, bool sam)
> >  {
> > -	struct in6_addr tmp = {};
> > +	struct in6_addr tmp;
> >  	u8 dam;
> >  
> >  	switch (lowpan_dev(dev)->lltype) {