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core/trivial: add code comment about DHCP client-id/DUID

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(cherry picked from commit e9630e7d57)
This commit is contained in:
Thomas Haller 2018-11-02 17:48:26 +01:00
parent 525830a4a0
commit 22ffd02f87
1 changed files with 26 additions and 0 deletions
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26
src/dhcp/nm-dhcp-manager.c
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@ -234,6 +234,32 @@ client_start (NMDhcpManager *self,
c_list_link_tail (&priv->dhcp_client_lst_head, &client->dhcp_client_lst);
g_signal_connect (client, NM_DHCP_CLIENT_SIGNAL_STATE_CHANGED, G_CALLBACK (client_state_changed), self);
/* unfortunately, our implementations work differently per address-family regarding client-id/DUID.
*
* - for IPv4, the calling code may determine a client-id (from NM's connection profile).
* If present, it is taken. If not present, the DHCP plugin uses a plugin specific default.
* - for "internal" plugin, the default is just "duid".
* - for "dhclient", we try to get the configuration from dhclient's /etc/dhcp or fallback
* to whatever dhclient uses by default.
* We do it this way, because for dhclient the user may configure a default
* outside of NM, and we want to honor that. Worse, dhclient could be a wapper
* script where the wrapper script overwrites the client-id. We need to distinguish
* between: force a particular client-id and leave it unspecified to whatever dhclient
* wants.
*
* - for IPv6, the calling code always determines a client-id. It also specifies @enforce_duid,
* to determine whether the given client-id must be used.
* - for "internal" plugin @enforce_duid doesn't matter and the given client-id is
* always used.
* - for "dhclient", @enforce_duid FALSE means to first try to load the DUID from the
* lease file, and only otherwise fallback to the given client-id.
* - other plugins don't support DHCPv6.
* It's done this way, so that existing dhclient setups don't change behavior on upgrade.
*
* This difference is cumbersome and only exists because of "dhclient" which supports hacking the
* default outside of NetworkManager API.
*/
if (addr_family == AF_INET) {
success = nm_dhcp_client_start_ip4 (client,
dhcp_client_id,