vfs_fruit: Time Machine/FULLSYNC: add mDNS/DNS-SD advertisement

[Omri Mor]

> On Jul 22, 2017, at 01:46, Ralph Böhme <slow at samba.org> wrote:
> 
>> On Sat, Jul 22, 2017 at 12:22:47AM -0700, Omri Mor wrote:
>> 
>> What string handling routines does Samba use?
> 
> The ones based on talloc, see
> <https://talloc.samba.org/talloc/doc/html/group__talloc__string.html>

Thanks for that!
I’ll more than likely need to use it for dns_sd; for Avahi it was far simpler to use their string list interface.

>> The sys record can be static though.
>> 
>> Samba has, apparently, a concept of service name and volume label; I’m not
>> sure which to use.  lp_servicename(), lp_volume(), or volume_label() (which
>> uses the volume if it exists, else the service name).
> 
> lp_servicename should do it.

I’ve used lp_const_servicename(), which seems to do the trick.

The Avahi portion is below—please tell me if there are any glaring errors or coding guideline violations.

The dns_sd interface is more difficult to work with.
Firstly, I think there are some bugs with it as it is:
While Avahi registers with the name from lp_netbios_name(), dns_sd pass NULL, which signifies using the default of the computer name (hostname).
This only differs when the ‘netbios name’ option is set (and differs from the hostname). This is likely an uncommon occurrence.

dns_register_smbd_fde_handler() appears to be bugged (badly) as well.
When the DNSServiceProcessResult() call succeeds, talloc_free() is called on the state struct, which in turn calls the destructor, which deregisters the service.
If the call fails, then the entire service is reinitialized.
I suspect the intent was:
on success, use tevent_add_fd() to wait for the next response
on failure, deregister and free the resources

If my understanding is correct, then dns_sd has been broken since 2009, when it was changed to be event-driven.
I suspect that the only platform using the dns_sd interface is macOS; since Apple ships its own SMB server, there isn’t much of a Samba userbase on the platform.
Samba isn’t even available in Homebrew, while the versions in MacPorts are ancient and unmaintained, as are those in Fink.
In short: is there even anyone using the dns_sd interface that would suffer from its removal?

Omri

diff --git a/source3/smbd/avahi_register.c b/source3/smbd/avahi_register.c
index 368168d..3e8d639 100644
--- a/source3/smbd/avahi_register.c
+++ b/source3/smbd/avahi_register.c
@@ -24,6 +24,7 @@
 #include <avahi-client/client.h>
 #include <avahi-client/publish.h>
 #include <avahi-common/error.h>
+#include <avahi-common/strlst.h>
 
 struct avahi_state_struct {
 	struct AvahiPoll *poll;
@@ -73,6 +74,10 @@ static void avahi_client_callback(AvahiClient *c, AvahiClientState status,
 	struct avahi_state_struct *state = talloc_get_type_abort(
 		userdata, struct avahi_state_struct);
 	int error;
+	int num_services;
+	int snum;
+	int dk;
+	AvahiStringList *adisk = NULL;
 
 	switch (status) {
 	case AVAHI_CLIENT_S_RUNNING:
@@ -97,6 +102,29 @@ static void avahi_client_callback(AvahiClient *c, AvahiClientState status,
 			state->entry_group = NULL;
 			break;
 		}
+		adisk = avahi_string_list_add(adisk, "sys=waMa=0,adVF=0x100");
+		num_services = lp_numservices();
+		dk = 0;
+		for (snum = 0; snum < num_services; snum++) {
+			if (lp_snum_ok(snum) &&
+			    lp_parm_bool(snum, "fruit", "time machine", false))
+			{
+				adisk = avahi_string_list_add_printf(adisk,
+					    "dk%d=adVN=%s,adVF=0x82",
+					    dk++, lp_const_servicename(snum));
+			}
+		}
+		if (dk > 0 && avahi_entry_group_add_service_strlst(
+			    state->entry_group, AVAHI_IF_UNSPEC,
+			    AVAHI_PROTO_UNSPEC, 0, lp_netbios_name(),
+			    "_adisk._tcp", NULL, NULL, 0, adisk) < 0) {
+			error = avahi_client_errno(c);
+			DEBUG(10, ("avahi_entry_group_add_service failed: "
+				   "%s\n", avahi_strerror(error)));
+			avahi_entry_group_free(state->entry_group);
+			state->entry_group = NULL;
+			break;
+		}
 		if (avahi_entry_group_commit(state->entry_group) < 0) {
 			error = avahi_client_errno(c);
 			DEBUG(10, ("avahi_entry_group_commit failed: "
@@ -138,6 +166,7 @@ static void avahi_client_callback(AvahiClient *c, AvahiClientState status,
 			   "AVAHI_CLIENT_CONNECTING\n"));
 		break;
 	}
+	avahi_string_list_free(adisk);
 }
 
 void *avahi_start_register(TALLOC_CTX *mem_ctx, struct tevent_context *ev,