mctp: Add SIOCMCTP{ALLOC,DROP}TAG ioctls for tag control

This change adds a couple of new ioctls for mctp sockets:
SIOCMCTPALLOCTAG and SIOCMCTPDROPTAG.  These ioctls provide facilities
for explicit allocation / release of tags, overriding the automatic
allocate-on-send/release-on-reply and timeout behaviours. This allows
userspace more control over messages that may not fit a simple
request/response model.

In order to indicate a pre-allocated tag to the sendmsg() syscall, we
introduce a new flag to the struct sockaddr_mctp.smctp_tag value:
MCTP_TAG_PREALLOC.

Additional changes from Jeremy Kerr <jk@codeconstruct.com.au>.

Contains a fix that was:
Reported-by: kernel test robot <lkp@intel.com>

Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 32 insertions, 2 deletions

diff --git a/include/net/mctp.h b/include/net/mctp.h
index 706d329dd8e8..e80a4baf8379 100644
--- a/include/net/mctp.h
+++ b/include/net/mctp.h
@@ -126,7 +126,7 @@ struct mctp_sock {
  */
 struct mctp_sk_key {
 	mctp_eid_t	peer_addr;
-	mctp_eid_t	local_addr;
+	mctp_eid_t	local_addr; /* MCTP_ADDR_ANY for local owned tags */
 	__u8		tag; /* incoming tag match; invert TO for local */
 
 	/* we hold a ref to sk when set */
@@ -163,6 +163,12 @@ struct mctp_sk_key {
 	 */
 	unsigned long	dev_flow_state;
 	struct mctp_dev	*dev;
+
+	/* a tag allocated with SIOCMCTPALLOCTAG ioctl will not expire
+	 * automatically on timeout or response, instead SIOCMCTPDROPTAG
+	 * is used.
+	 */
+	bool		manual_alloc;
 };
 
 struct mctp_skb_cb {
@@ -239,6 +245,9 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
 		      struct sk_buff *skb, mctp_eid_t daddr, u8 req_tag);
 
 void mctp_key_unref(struct mctp_sk_key *key);
+struct mctp_sk_key *mctp_alloc_local_tag(struct mctp_sock *msk,
+					 mctp_eid_t daddr, mctp_eid_t saddr,
+					 bool manual, u8 *tagp);
 
 /* routing <--> device interface */
 unsigned int mctp_default_net(struct net *net);
diff --git a/include/trace/events/mctp.h b/include/trace/events/mctp.h
index 175b057c507f..165cf25f77a7 100644
--- a/include/trace/events/mctp.h
+++ b/include/trace/events/mctp.h
@@ -15,6 +15,7 @@ enum {
 	MCTP_TRACE_KEY_REPLIED,
 	MCTP_TRACE_KEY_INVALIDATED,
 	MCTP_TRACE_KEY_CLOSED,
+	MCTP_TRACE_KEY_DROPPED,
 };
 #endif /* __TRACE_MCTP_ENUMS */
 
@@ -22,6 +23,7 @@ TRACE_DEFINE_ENUM(MCTP_TRACE_KEY_TIMEOUT);
 TRACE_DEFINE_ENUM(MCTP_TRACE_KEY_REPLIED);
 TRACE_DEFINE_ENUM(MCTP_TRACE_KEY_INVALIDATED);
 TRACE_DEFINE_ENUM(MCTP_TRACE_KEY_CLOSED);
+TRACE_DEFINE_ENUM(MCTP_TRACE_KEY_DROPPED);
 
 TRACE_EVENT(mctp_key_acquire,
 	TP_PROTO(const struct mctp_sk_key *key),
@@ -66,7 +68,8 @@ TRACE_EVENT(mctp_key_release,
 				 { MCTP_TRACE_KEY_TIMEOUT, "timeout" },
 				 { MCTP_TRACE_KEY_REPLIED, "replied" },
 				 { MCTP_TRACE_KEY_INVALIDATED, "invalidated" },
-				 { MCTP_TRACE_KEY_CLOSED, "closed" })
+				 { MCTP_TRACE_KEY_CLOSED, "closed" },
+				 { MCTP_TRACE_KEY_DROPPED, "dropped" })
 	)
 );
 
diff --git a/include/uapi/linux/mctp.h b/include/uapi/linux/mctp.h
index 07b0318716fc..154ab56651f1 100644
--- a/include/uapi/linux/mctp.h
+++ b/include/uapi/linux/mctp.h
@@ -44,7 +44,25 @@ struct sockaddr_mctp_ext {
 
 #define MCTP_TAG_MASK		0x07
 #define MCTP_TAG_OWNER		0x08
+#define MCTP_TAG_PREALLOC	0x10
 
 #define MCTP_OPT_ADDR_EXT	1
 
+#define SIOCMCTPALLOCTAG	(SIOCPROTOPRIVATE + 0)
+#define SIOCMCTPDROPTAG		(SIOCPROTOPRIVATE + 1)
+
+struct mctp_ioc_tag_ctl {
+	mctp_eid_t	peer_addr;
+
+	/* For SIOCMCTPALLOCTAG: must be passed as zero, kernel will
+	 * populate with the allocated tag value. Returned tag value will
+	 * always have TO and PREALLOC set.
+	 *
+	 * For SIOCMCTPDROPTAG: userspace provides tag value to drop, from
+	 * a prior SIOCMCTPALLOCTAG call (and so must have TO and PREALLOC set).
+	 */
+	__u8		tag;
+	__u16		flags;
+};
+
 #endif /* __UAPI_MCTP_H */