[PATCH conntrack] conntrack: label update requires a previous label in place

[Pablo Neira Ayuso <pablo@netfilter.org>]

You have to set an initial label if you plan to update it later on.  If
conntrack comes with no initial label, then it is not possible to attach
it later because conntrack extensions are created by the time the new
entry is created.

Update manpage to document this behaviour.

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1622
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 conntrack.8 | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/conntrack.8 b/conntrack.8
index 031eaa4e9fef..f3610b15d4a6 100644
--- a/conntrack.8
+++ b/conntrack.8
@@ -193,6 +193,9 @@ Use multiple \-l options to specify multiple labels that need to be set.
 Specify the conntrack label to add to the selected conntracks.
 This option is only available in conjunction with "\-I, \-\-create",
 "\-A, \-\-add" or "\-U, \-\-update".
+You must set a default label for conntracks initially if you plan to update it
+later, that is, "\-U, \-\-update" requires an initial label already. If you
+update a conntrack entry without an initial label, an error will be reported.
 .TP
 .BI "--label-del " "[LABEL]"
 Specify the conntrack label to delete from the selected conntracks.
-- 
2.30.2