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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>
This commit is contained in:
David S. Miller
2012-07-19 12:31:33 -07:00
parent f8126f1d51
commit f5b0a87436
7 changed files with 35 additions and 21 deletions
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23
net/xfrm/xfrm_policy.c
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@@ -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;
@@ -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;
@@ -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
*
@@ -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;