[PATCH v2] genl: modify genl_ctrl_resolve and friends to allow for module auto-loading

Thomas Graf tgraf at infradead.org
Sun Jun 3 07:59:59 EDT 2012


On Fri, Jun 01, 2012 at 12:59:24PM -0400, Neil Horman wrote:
> Generic netlink has the ability to autoload modules in response to a request for
> a family.  Currently libnl uses a GETFAMILY call with the NLM_F_DUMP flag to
> list all the available families, but doing so neglects the possibility of an
> autoloaded module.  This patch modifies the genl code to probe the kernel for a
> specific family rather than dumping a list of all the currenlty available ones,
> making autoload work properly.

Applied, thanks Neil!

I took the liberty to slightly modify the patch. I hope you don't mind.

I changed genl_ctrl_probe_by_name() to create a clone of the socket cb
structure instead of modying it directly. This avoids overwriting the
NL_CB_VALID callback a user might have set on the socket.

I moved the mcast parsing code into its own function to share it with
the msg_parser() function.

I added a small test case to tests/test-genl.c to run genl_ctrl_resolve()
and make sure it works.

Maybe you can have a quick look over the new patch and yell if you
disagree with anything

commit 0c408aad1fc564b53d6382f1076019a7694adff4
Author: Neil Horman <nhorman at tuxdriver.com>
Date:   Fri Jun 1 12:59:24 2012 -0400

    genl: modify genl_ctrl_resolve and friends to allow for module auto-loading
    
    Generic netlink has the ability to autoload modules in response to a request for
    a family.  Currently libnl uses a GETFAMILY call with the NLM_F_DUMP flag to
    list all the available families, but doing so neglects the possibility of an
    autoloaded module.  This patch modifies the genl code to probe the kernel for a
    specific family rather than dumping a list of all the currenlty available ones,
    making autoload work properly.
    
    Signed-off-by: Neil Horman <nhorman at tuxdriver.com>
    CC: Thomas Graf <tgraf at redhat.com>

diff --git a/lib/genl/ctrl.c b/lib/genl/ctrl.c
index ddb7603..3902f09 100644
--- a/lib/genl/ctrl.c
+++ b/lib/genl/ctrl.c
@@ -61,6 +61,47 @@ static struct nla_policy family_grp_policy[CTRL_ATTR_MCAST_GRP_MAX+1] = {
        [CTRL_ATTR_MCAST_GRP_ID]   = { .type = NLA_U32 },
 };
 
+static int parse_mcast_grps(struct genl_family *family, struct nlattr *grp_attr)
+{
+       struct nlattr *nla;
+       int remaining, err;
+
+       if (!grp_attr)
+               BUG();
+
+       nla_for_each_nested(nla, grp_attr, remaining) {
+               struct nlattr *tb[CTRL_ATTR_MCAST_GRP_MAX+1];
+               int id;
+               const char * name;
+
+               err = nla_parse_nested(tb, CTRL_ATTR_MCAST_GRP_MAX, nla,
+                                      family_grp_policy);
+               if (err < 0)
+                       goto errout;
+
+               if (tb[CTRL_ATTR_MCAST_GRP_ID] == NULL) {
+                       err = -NLE_MISSING_ATTR;
+                       goto errout;
+               }
+               id = nla_get_u32(tb[CTRL_ATTR_MCAST_GRP_ID]);
+
+               if (tb[CTRL_ATTR_MCAST_GRP_NAME] == NULL) {
+                       err = -NLE_MISSING_ATTR;
+                       goto errout;
+               }
+               name = nla_get_string(tb[CTRL_ATTR_MCAST_GRP_NAME]);
+
+               err = genl_family_add_grp(family, id, name);
+               if (err < 0)
+                       goto errout;
+       }
+
+       err = 0;
+
+errout:
       return err;
+}
+
 static int ctrl_msg_parser(struct nl_cache_ops *ops, struct genl_cmd *cmd,
                           struct genl_info *info, void *arg)
 {
@@ -137,45 +178,115 @@ static int ctrl_msg_parser(struct nl_cache_ops *ops, struct genl_cmd *cmd,
        }
        
        if (info->attrs[CTRL_ATTR_MCAST_GROUPS]) {
-               struct nlattr *nla, *nla_grps;
-               int remaining;
+               err = parse_mcast_grps(family, info->attrs[CTRL_ATTR_MCAST_GROUPS]);
+               if (err < 0)
+                       goto errout;
+       }
 
-               nla_grps = info->attrs[CTRL_ATTR_MCAST_GROUPS];
-               nla_for_each_nested(nla, nla_grps, remaining) {
-                       struct nlattr *tb[CTRL_ATTR_MCAST_GRP_MAX+1];
-                       int id;
-                       const char * name;
+       err = pp->pp_cb((struct nl_object *) family, pp);
+errout:
+       genl_family_put(family);
+       return err;
+}
 
-                       err = nla_parse_nested(tb, CTRL_ATTR_MCAST_GRP_MAX, nla,
-                                              family_grp_policy);
-                       if (err < 0)
-                               goto errout;
+/**
+ * process responses from from the query sent by genl_ctrl_probe_by_name 
+ * @arg nl_msg         Returned message.
+ * @arg name           genl_family structure to fill out.
+ *
+ * Process returned messages, filling out the missing informatino in the
+ * genl_family structure
+ *
+ * @return Indicator to keep processing frames or not
+ *
+ */
+static int probe_response(struct nl_msg *msg, void *arg)
+{
+       struct nlattr *tb[CTRL_ATTR_MAX+1];
+       struct nlmsghdr *nlh = nlmsg_hdr(msg);
+       struct genl_family *ret = (struct genl_family *)arg;
 
-                       if (tb[CTRL_ATTR_MCAST_GRP_ID] == NULL) {
-                               err = -NLE_MISSING_ATTR;
-                               goto errout;
-                       }
-                       id = nla_get_u32(tb[CTRL_ATTR_MCAST_GRP_ID]);
+       if (genlmsg_parse(nlh, 0, tb, CTRL_ATTR_MAX, ctrl_policy))
+               return NL_SKIP;
 
-                       if (tb[CTRL_ATTR_MCAST_GRP_NAME] == NULL) {
-                               err = -NLE_MISSING_ATTR;
-                               goto errout;
-                       }
-                       name = nla_get_string(tb[CTRL_ATTR_MCAST_GRP_NAME]);
+       if (tb[CTRL_ATTR_FAMILY_ID])
+               genl_family_set_id(ret, nla_get_u16(tb[CTRL_ATTR_FAMILY_ID]));
 
-                       err = genl_family_add_grp(family, id, name);
-                       if (err < 0)
-                               goto errout;
-               }
+       if (tb[CTRL_ATTR_MCAST_GROUPS])
+               if (parse_mcast_grps(ret, tb[CTRL_ATTR_MCAST_GROUPS]) < 0)
+                       return NL_SKIP;
+
+       return NL_STOP;
+}
+
+/**
+ * Look up generic netlink family by family name querying the kernel directly
+ * @arg sk             Socket.
+ * @arg name           Family name.
+ *
+ * Directly query's the kernel for a given family name.  The caller will own a
+ * reference on the returned object which needsd to be given back after usage
+ * using genl_family_put.
+ *
+ * Note: This API call differs from genl_ctrl_search_by_name in that it querys
+ * the kernel directly, alowing for module autoload to take place to resolve the
+ * family request. Using an nl_cache prevents that operation
+ *
+ * @return Generic netlink family object or NULL if no match was found.
+ */
+static struct genl_family *genl_ctrl_probe_by_name(struct nl_sock *sk, const char *name)
+{
+       struct nl_msg *msg;
+       struct genl_family *ret = NULL;
+       struct nl_cb *cb;
+       int rc;
+
+       ret = genl_family_alloc();
+       if (!ret)
+               goto out;
+
+       genl_family_set_name(ret, name);
+
+       msg = nlmsg_alloc();
+       if (!msg)
+               goto out_fam_free;
 
+       if (!(cb = nl_cb_clone(nl_socket_get_cb(sk))))
+               goto out_msg_free;
+
+
+       genlmsg_put(msg, NL_AUTO_PID, NL_AUTO_SEQ, GENL_ID_CTRL,
+                   0, 0, CTRL_CMD_GETFAMILY, 1);
+
+       if (nla_put_string(msg, CTRL_ATTR_FAMILY_NAME, name))
+               goto out_cb_free;
+
+       rc = nl_send_auto_complete(sk, msg);
+       if (rc < 0)
+               goto out_cb_free;
+
+       nl_cb_set(cb, NL_CB_VALID, NL_CB_CUSTOM, probe_response, (void *)ret);
+
+       nl_recvmsgs(sk, cb);
+
+       if (genl_family_get_id(ret) != 0) {
+               nlmsg_free(msg);
+               nl_cb_put(cb);
+               return ret;
        }
 
-       err = pp->pp_cb((struct nl_object *) family, pp);
-errout:
-       genl_family_put(family);
-       return err;
+out_cb_free:
+       nl_cb_put(cb);
+out_msg_free:
+       nlmsg_free(msg);
+out_fam_free:
+       genl_family_put(ret);
+       ret = NULL;
+out:
+       return ret;
 }
 
+
 /** @endcond */
 
 /**
@@ -299,14 +410,10 @@ struct genl_family *genl_ctrl_search_by_name(struct nl_cache *cache,
  */
 int genl_ctrl_resolve(struct nl_sock *sk, const char *name)
 {
-       struct nl_cache *cache;
        struct genl_family *family;
        int err;
 
-       if ((err = genl_ctrl_alloc_cache(sk, &cache)) < 0)
-               return err;
-
-       family = genl_ctrl_search_by_name(cache, name);
+       family = genl_ctrl_probe_by_name(sk, name);
        if (family == NULL) {
                err = -NLE_OBJ_NOTFOUND;
                goto errout;
@@ -315,8 +422,6 @@ int genl_ctrl_resolve(struct nl_sock *sk, const char *name)
        err = genl_family_get_id(family);
        genl_family_put(family);
 errout:
-       nl_cache_free(cache);
-
        return err;
 }
 
@@ -348,14 +453,11 @@ static int genl_ctrl_grp_by_name(const struct genl_family *family,
 int genl_ctrl_resolve_grp(struct nl_sock *sk, const char *family_name,
                          const char *grp_name)
 {
-       struct nl_cache *cache;
+
        struct genl_family *family;
        int err;
 
-       if ((err = genl_ctrl_alloc_cache(sk, &cache)) < 0)
-               return err;
-
-       family = genl_ctrl_search_by_name(cache, family_name);
+       family = genl_ctrl_probe_by_name(sk, family_name);
        if (family == NULL) {
                err = -NLE_OBJ_NOTFOUND;
                goto errout;
@@ -364,8 +466,6 @@ int genl_ctrl_resolve_grp(struct nl_sock *sk, const char *family_name,
        err = genl_ctrl_grp_by_name(family, grp_name);
        genl_family_put(family);
 errout:
-       nl_cache_free(cache);
-
        return err;
 }
 
diff --git a/tests/test-genl.c b/tests/test-genl.c
index 63862b3..74aea10 100644
--- a/tests/test-genl.c
+++ b/tests/test-genl.c
@@ -84,6 +84,9 @@ int main(int argc, char *argv[])
        if ((err = genl_ops_resolve(sock, &ops)) < 0)
                nl_cli_fatal(err, "Unable to resolve family name");
 
+       if (genl_ctrl_resolve(sock, "nlctrl") != GENL_ID_CTRL)
+               nl_cli_fatal(NLE_INVAL, "Resolving of \"nlctrl\" failed");
+
        msg = nlmsg_alloc();
        if (msg == NULL)
                nl_cli_fatal(NLE_NOMEM, "Unable to allocate netlink message");




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