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 <[email protected]> --- 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
