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net: Document dst->obsolete better.
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Add a big comment explaining how the field works, and use defines
instead of magic constants for the values assigned to it.

Suggested by Joe Perches.

Signed-off-by: David S. Miller <davem@davemloft.net>
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@davem330
davem330 committed Jul 20, 2012
1 parent f8126f1 commit f5b0a87
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Showing 7 changed files with 35 additions and 21 deletions.
14 changes: 13 additions & 1 deletion include/net/dst.h
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Original file line number Diff line number Diff line change
Expand Up @@ -65,7 +65,19 @@ struct dst_entry {
unsigned short pending_confirm;

short error;

/* A non-zero value of dst->obsolete forces by-hand validation
* of the route entry. Positive values are set by the generic
* dst layer to indicate that the entry has been forcefully
* destroyed.
*
* Negative values are used by the implementation layer code to
* force invocation of the dst_ops->check() method.
*/
short obsolete;
#define DST_OBSOLETE_NONE 0
#define DST_OBSOLETE_DEAD 2
#define DST_OBSOLETE_FORCE_CHK -1
unsigned short header_len; /* more space at head required */
unsigned short trailer_len; /* space to reserve at tail */
#ifdef CONFIG_IP_ROUTE_CLASSID
Expand Down Expand Up @@ -359,7 +371,7 @@ extern struct dst_entry *dst_destroy(struct dst_entry *dst);

static inline void dst_free(struct dst_entry *dst)
{
if (dst->obsolete > 1)
if (dst->obsolete > 0)
return;
if (!atomic_read(&dst->__refcnt)) {
dst = dst_destroy(dst);
Expand Down
4 changes: 2 additions & 2 deletions net/core/dst.c
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,7 @@ static void dst_gc_task(struct work_struct *work)
* But we do not have state "obsoleted, but
* referenced by parent", so it is right.
*/
if (dst->obsolete > 1)
if (dst->obsolete > 0)
continue;

___dst_free(dst);
Expand Down Expand Up @@ -202,7 +202,7 @@ static void ___dst_free(struct dst_entry *dst)
*/
if (dst->dev == NULL || !(dst->dev->flags&IFF_UP))
dst->input = dst->output = dst_discard;
dst->obsolete = 2;
dst->obsolete = DST_OBSOLETE_DEAD;
}

void __dst_free(struct dst_entry *dst)
Expand Down
4 changes: 2 additions & 2 deletions net/decnet/dn_route.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1176,7 +1176,7 @@ static int dn_route_output_slow(struct dst_entry **pprt, const struct flowidn *o
if (dev_out->flags & IFF_LOOPBACK)
flags |= RTCF_LOCAL;

rt = dst_alloc(&dn_dst_ops, dev_out, 1, 0, DST_HOST);
rt = dst_alloc(&dn_dst_ops, dev_out, 1, DST_OBSOLETE_NONE, DST_HOST);
if (rt == NULL)
goto e_nobufs;

Expand Down Expand Up @@ -1444,7 +1444,7 @@ static int dn_route_input_slow(struct sk_buff *skb)
}

make_route:
rt = dst_alloc(&dn_dst_ops, out_dev, 0, 0, DST_HOST);
rt = dst_alloc(&dn_dst_ops, out_dev, 0, DST_OBSOLETE_NONE, DST_HOST);
if (rt == NULL)
goto e_nobufs;

Expand Down
5 changes: 3 additions & 2 deletions net/ipv4/route.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1221,7 +1221,7 @@ static void rt_set_nexthop(struct rtable *rt, const struct flowi4 *fl4,
static struct rtable *rt_dst_alloc(struct net_device *dev,
bool nopolicy, bool noxfrm)
{
return dst_alloc(&ipv4_dst_ops, dev, 1, -1,
return dst_alloc(&ipv4_dst_ops, dev, 1, DST_OBSOLETE_FORCE_CHK,
DST_HOST | DST_NOCACHE |
(nopolicy ? DST_NOPOLICY : 0) |
(noxfrm ? DST_NOXFRM : 0));
Expand Down Expand Up @@ -1969,9 +1969,10 @@ static struct dst_ops ipv4_dst_blackhole_ops = {

struct dst_entry *ipv4_blackhole_route(struct net *net, struct dst_entry *dst_orig)
{
struct rtable *rt = dst_alloc(&ipv4_dst_blackhole_ops, NULL, 1, 0, 0);
struct rtable *ort = (struct rtable *) dst_orig;
struct rtable *rt;

rt = dst_alloc(&ipv4_dst_blackhole_ops, NULL, 1, DST_OBSOLETE_NONE, 0);
if (rt) {
struct dst_entry *new = &rt->dst;

Expand Down
4 changes: 2 additions & 2 deletions net/ipv6/route.c
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Original file line number Diff line number Diff line change
Expand Up @@ -281,7 +281,7 @@ static inline struct rt6_info *ip6_dst_alloc(struct net *net,
struct fib6_table *table)
{
struct rt6_info *rt = dst_alloc(&net->ipv6.ip6_dst_ops, dev,
0, 0, flags);
0, DST_OBSOLETE_NONE, flags);

if (rt) {
struct dst_entry *dst = &rt->dst;
Expand Down Expand Up @@ -985,7 +985,7 @@ struct dst_entry *ip6_blackhole_route(struct net *net, struct dst_entry *dst_ori
struct rt6_info *rt, *ort = (struct rt6_info *) dst_orig;
struct dst_entry *new = NULL;

rt = dst_alloc(&ip6_dst_blackhole_ops, ort->dst.dev, 1, 0, 0);
rt = dst_alloc(&ip6_dst_blackhole_ops, ort->dst.dev, 1, DST_OBSOLETE_NONE, 0);
if (rt) {
new = &rt->dst;

Expand Down
2 changes: 1 addition & 1 deletion net/sctp/transport.c
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Original file line number Diff line number Diff line change
Expand Up @@ -216,7 +216,7 @@ void sctp_transport_set_owner(struct sctp_transport *transport,
void sctp_transport_pmtu(struct sctp_transport *transport, struct sock *sk)
{
/* If we don't have a fresh route, look one up */
if (!transport->dst || transport->dst->obsolete > 1) {
if (!transport->dst || transport->dst->obsolete) {
dst_release(transport->dst);
transport->af_specific->get_dst(transport, &transport->saddr,
&transport->fl, sk);
Expand Down
23 changes: 12 additions & 11 deletions net/xfrm/xfrm_policy.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1350,7 +1350,7 @@ static inline struct xfrm_dst *xfrm_alloc_dst(struct net *net, int family)
default:
BUG();
}
xdst = dst_alloc(dst_ops, NULL, 0, 0, 0);
xdst = dst_alloc(dst_ops, NULL, 0, DST_OBSOLETE_NONE, 0);

if (likely(xdst)) {
struct dst_entry *dst = &xdst->u.dst;
Expand Down Expand Up @@ -1477,7 +1477,7 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy,
dst1->xfrm = xfrm[i];
xdst->xfrm_genid = xfrm[i]->genid;

dst1->obsolete = -1;
dst1->obsolete = DST_OBSOLETE_FORCE_CHK;
dst1->flags |= DST_HOST;
dst1->lastuse = now;

Expand Down Expand Up @@ -2219,12 +2219,13 @@ EXPORT_SYMBOL(__xfrm_route_forward);
static struct dst_entry *xfrm_dst_check(struct dst_entry *dst, u32 cookie)
{
/* Code (such as __xfrm4_bundle_create()) sets dst->obsolete
* to "-1" to force all XFRM destinations to get validated by
* dst_ops->check on every use. We do this because when a
* normal route referenced by an XFRM dst is obsoleted we do
* not go looking around for all parent referencing XFRM dsts
* so that we can invalidate them. It is just too much work.
* Instead we make the checks here on every use. For example:
* to DST_OBSOLETE_FORCE_CHK to force all XFRM destinations to
* get validated by dst_ops->check on every use. We do this
* because when a normal route referenced by an XFRM dst is
* obsoleted we do not go looking around for all parent
* referencing XFRM dsts so that we can invalidate them. It
* is just too much work. Instead we make the checks here on
* every use. For example:
*
* XFRM dst A --> IPv4 dst X
*
Expand All @@ -2234,9 +2235,9 @@ static struct dst_entry *xfrm_dst_check(struct dst_entry *dst, u32 cookie)
* stale_bundle() check.
*
* When a policy's bundle is pruned, we dst_free() the XFRM
* dst which causes it's ->obsolete field to be set to a
* positive non-zero integer. If an XFRM dst has been pruned
* like this, we want to force a new route lookup.
* dst which causes it's ->obsolete field to be set to
* DST_OBSOLETE_DEAD. If an XFRM dst has been pruned like
* this, we want to force a new route lookup.
*/
if (dst->obsolete < 0 && !stale_bundle(dst))
return dst;
Expand Down

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