There is some ambiguity in how various drivers support
NL80211_CMD_SET_INTERFACE on devices where the underlying netdev is UP.
mac80211 for example supports this if the underlying driver provides a
change_interface operation. However, most devices do not. For FullMac
devices, the situation is even less clear.
This patch introduces a new feature flag that lets userspace know
whether it can expect a mode change (via SET_INTERFACE) to work while
the device is still UP or it should bring down the device first.
This commit also updates the documentation for SET_INTERFACE with hints
as to how it should be used.
Signed-off-by: Denis Kenzior <denkenz@xxxxxxxxx>
---
include/uapi/linux/nl80211.h | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
diff --git a/include/uapi/linux/nl80211.h b/include/uapi/linux/nl80211.h
index bf7c4222f512..a9ca2fe67f52 100644
--- a/include/uapi/linux/nl80211.h
+++ b/include/uapi/linux/nl80211.h
@@ -275,6 +275,29 @@
* single %NL80211_ATTR_IFINDEX is supported.
* @NL80211_CMD_SET_INTERFACE: Set type of a virtual interface, requires
* %NL80211_ATTR_IFINDEX and %NL80211_ATTR_IFTYPE.
+ *
+ * Note that it is driver-dependent whether a SET_INTERFACE will be
+ * allowed if the underlying netdev is currently UP. Userspace
+ * can obtain a hint as to whether this is allowed by looking at
+ * the %NL80211_EXT_FEATURE_LIVE_IFTYPE_CHANGE, but certain restrictions
+ * will still apply.
+ *
+ * Prior to Kernel 5.4, userspace applications should implement the
+ * following behavior:
+ * 1. (Optionally) Attempt SET_INTERFACE on a wireless device
+ * with the underlying netdev in the UP state. If -EBUSY
+ * is returned proceed to 2. Note that a SET_INTERFACE
+ * which results in -EBUSY might still result in other
+ * side-effects, such as Deauthentication, exiting AP mode,
+ * etc.
+ * 2. Bring the netdev DOWN via RTNL
+ * 3. Attempt SET_INTERFACE on the underlying netdev in the DOWN
+ * state. If successful, proceed to 4.
+ * 4. Bring the netdev UP via RTNL
+ *
+ * Note that bringing down the device might trigger a firmware reset /
+ * power cycling and/or other effects that are driver dependent.
+ *
* @NL80211_CMD_NEW_INTERFACE: Newly created virtual interface or response
* to %NL80211_CMD_GET_INTERFACE. Has %NL80211_ATTR_IFINDEX,
* %NL80211_ATTR_WIPHY and %NL80211_ATTR_IFTYPE attributes. Can also
@@ -5481,6 +5504,18 @@ enum nl80211_feature_flags {
* @NL80211_EXT_FEATURE_SAE_OFFLOAD: Device wants to do SAE authentication in
* station mode (SAE password is passed as part of the connect command).
*
+ * @NL80211_EXT_FEATURE_LIVE_IFTYPE_CHANGE: This device supports switching
+ * the IFTYPE of an interface without having to bring the device DOWN
+ * first via RTNL. Exact semantics of this feature is driver
+ * implementation dependent. For mac80211, the following restrictions
+ * apply:
+ * - Only devices currently in IFTYPE AP, P2P_GO, P2P_CLIENT,
+ * STATION, ADHOC and OCB can be switched.
+ * - The target IFTYPE must be one of: AP, P2P_GO, P2P_CLIENT,
+ * STATION, ADHOC or OCB.
+ * Other drivers are expected to follow similar restrictions.
+ * This flag was introduced in Kernel v5.4
+ *
* @NUM_NL80211_EXT_FEATURES: number of extended features.
* @MAX_NL80211_EXT_FEATURES: highest extended feature index.
*/
@@ -5526,6 +5561,7 @@ enum nl80211_ext_feature_index {
NL80211_EXT_FEATURE_EXT_KEY_ID,
NL80211_EXT_FEATURE_STA_TX_PWR,
NL80211_EXT_FEATURE_SAE_OFFLOAD,
+ NL80211_EXT_FEATURE_LIVE_IFTYPE_CHANGE,
/* add new features before the definition below */
NUM_NL80211_EXT_FEATURES,
--
2.19.2
