Thread-safe error handling

In order for the interface to become more thread safe, the error
handling was revised to no longer depend on a static errno and
error string buffer.

This patch converts all error paths to return a libnl specific
error code which can be translated to a error message using
nl_geterror(int error). The functions nl_error() and
nl_get_errno() are therefore obsolete.

This change required various sets of function prototypes to be
changed in order to return an error code, the most prominent
are:

    struct nl_cache *foo_alloc_cache(...);
changed to:
    int foo_alloc_cache(..., struct nl_cache **);

    struct nl_msg *foo_build_request(...);
changed to:
    int foo_build_request(..., struct nl_msg **);

    struct foo *foo_parse(...);
changed to:
    int foo_parse(..., struct foo **);

This pretty much only leaves trivial allocation functions to
still return a pointer object which can still return NULL to
signal out of memory.

This change is a serious API and ABI breaker, sorry!

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/route/qdisc_api.c b/lib/route/qdisc_api.c
index ef4d07a..089f212 100644
--- a/lib/route/qdisc_api.c
+++ b/lib/route/qdisc_api.c
@@ -46,7 +46,7 @@ int rtnl_qdisc_register(struct rtnl_qdisc_ops *qops)
 
 	for (op = &qdisc_ops_list; (o = *op) != NULL; op = &o->qo_next)
 		if (!strcasecmp(qops->qo_kind, o->qo_kind))
-			return nl_errno(EEXIST);
+			return -NLE_EXIST;
 
 	qops->qo_next = NULL;
 	*op = qops;
@@ -67,7 +67,7 @@ int rtnl_qdisc_unregister(struct rtnl_qdisc_ops *qops)
 			break;
 
 	if (!o)
-		return nl_errno(ENOENT);
+		return -NLE_OBJ_NOTFOUND;
 
 	*op = qops->qo_next;