[PATCH 2/3] tun: reuse IFF_ flags internally

["Michael S. Tsirkin" <mst@redhat.com>]

By reusing IFF_ flags for internal tun device flags,
we can get rid of a bunch of code translating back
and forth.

This cleanup exposes a bug: TUNGETFEATURES reports IFF_TUN and IFF_TAP
which aren't legal for TUNSETFEATURES (but, correctly, doesn't report
IFF_PERSIST which also isn't legal there).

I'm not fixing this bug at the moment, just in case some weird
userspace depends on it, using TUNGETFEATURES to check device type.

Follow-up patches will get rid of some of TUN_ macros,
using IFF_ directly instead.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/net/tun.c | 83 +++++++++++++++----------------------------------------
 1 file changed, 22 insertions(+), 61 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 81735f5..e4bd542 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -104,19 +104,23 @@ do {								\
 #endif
 
 /* TUN device flags */
-#define TUN_TUN_DEV 	0x0001
-#define TUN_TAP_DEV	0x0002
-#define TUN_TYPE_MASK   0x000f
+#define TUN_TUN_DEV 	IFF_TUN
+#define TUN_TAP_DEV	IFF_TAP
+#define TUN_TYPE_MASK   (IFF_TUN | IFF_TAP)
 
-#define TUN_FASYNC	0x0010
-#define TUN_NOCHECKSUM	0x0020
-#define TUN_NO_PI	0x0040
+/* IFF_ATTACH_QUEUE is never stored in device flags,
+ * overload it to mean fasync when stored there.
+ */
+#define TUN_FASYNC	IFF_ATTACH_QUEUE
+#define TUN_NO_PI	IFF_NO_PI
 /* This flag has no real effect */
-#define TUN_ONE_QUEUE	0x0080
-#define TUN_PERSIST 	0x0100
-#define TUN_VNET_HDR 	0x0200
-#define TUN_TAP_MQ      0x0400
+#define TUN_ONE_QUEUE	IFF_ONE_QUEUE
+#define TUN_PERSIST 	IFF_PERSIST
+#define TUN_VNET_HDR 	IFF_VNET_HDR
+#define TUN_TAP_MQ      IFF_MULTI_QUEUE
 
+#define TUN_FEATURES (IFF_NO_PI | IFF_ONE_QUEUE | IFF_VNET_HDR | \
+		      IFF_MULTI_QUEUE)
 #define GOODCOPY_LEN 128
 
 #define FLT_EXACT_COUNT 8
@@ -1529,32 +1533,7 @@ static struct proto tun_proto = {
 
 static int tun_flags(struct tun_struct *tun)
 {
-	int flags = 0;
-
-	if (tun->flags & TUN_TUN_DEV)
-		flags |= IFF_TUN;
-	else
-		flags |= IFF_TAP;
-
-	if (tun->flags & TUN_NO_PI)
-		flags |= IFF_NO_PI;
-
-	/* This flag has no real effect.  We track the value for backwards
-	 * compatibility.
-	 */
-	if (tun->flags & TUN_ONE_QUEUE)
-		flags |= IFF_ONE_QUEUE;
-
-	if (tun->flags & TUN_VNET_HDR)
-		flags |= IFF_VNET_HDR;
-
-	if (tun->flags & TUN_TAP_MQ)
-		flags |= IFF_MULTI_QUEUE;
-
-	if (tun->flags & TUN_PERSIST)
-		flags |= IFF_PERSIST;
-
-	return flags;
+	return tun->flags & (TUN_FEATURES | IFF_PERSIST | IFF_TUN | IFF_TAP);
 }
 
 static ssize_t tun_show_flags(struct device *dev, struct device_attribute *attr,
@@ -1714,28 +1693,8 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
 
 	tun_debug(KERN_INFO, tun, "tun_set_iff\n");
 
-	if (ifr->ifr_flags & IFF_NO_PI)
-		tun->flags |= TUN_NO_PI;
-	else
-		tun->flags &= ~TUN_NO_PI;
-
-	/* This flag has no real effect.  We track the value for backwards
-	 * compatibility.
-	 */
-	if (ifr->ifr_flags & IFF_ONE_QUEUE)
-		tun->flags |= TUN_ONE_QUEUE;
-	else
-		tun->flags &= ~TUN_ONE_QUEUE;
-
-	if (ifr->ifr_flags & IFF_VNET_HDR)
-		tun->flags |= TUN_VNET_HDR;
-	else
-		tun->flags &= ~TUN_VNET_HDR;
-
-	if (ifr->ifr_flags & IFF_MULTI_QUEUE)
-		tun->flags |= TUN_TAP_MQ;
-	else
-		tun->flags &= ~TUN_TAP_MQ;
+	tun->flags = (tun->flags & ~TUN_FEATURES) |
+		(ifr->ifr_flags & TUN_FEATURES);
 
 	/* Make sure persistent devices do not get stuck in
 	 * xoff state.
@@ -1898,9 +1857,11 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	if (cmd == TUNGETFEATURES) {
 		/* Currently this just means: "what IFF flags are valid?".
 		 * This is needed because we never checked for invalid flags on
-		 * TUNSETIFF. */
-		return put_user(IFF_TUN | IFF_TAP | IFF_NO_PI | IFF_ONE_QUEUE |
-				IFF_VNET_HDR | IFF_MULTI_QUEUE,
+		 * TUNSETIFF.  Why do we report IFF_TUN and IFF_TAP which are
+		 * not legal for TUNSETIFF here?  It's probably a bug, but it
+		 * doesn't seem to be worth fixing.
+		 */
+		return put_user(IFF_TUN | IFF_TAP | TUN_FEATURES,
 				(unsigned int __user*)argp);
 	} else if (cmd == TUNSETQUEUE)
 		return tun_set_queue(file, &ifr);
-- 
MST