Replace hardcoded 11 with a define

The 11 comes from the legacy API that we need to be binary compatible with.
Make this clear with a define and a comment.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

3 files changed, 18 insertions, 10 deletions

diff --git a/src/caps.c b/src/caps.c
index 45c185c..2e6b0d4 100644
--- a/src/caps.c
+++ b/src/caps.c
@@ -61,10 +61,10 @@ static struct input_absinfo *get_info(struct mtdev *dev, int code)
                 return NULL;
 
         ix = mtdev_abs2mt(code);
-        if (ix < 11)
+        if (ix < LEGACY_API_NUM_MT_AXES)
                 return &dev->abs[ix];
         else
-                return &dev->state->ext_abs[ix - 11];
+                return &dev->state->ext_abs[ix - LEGACY_API_NUM_MT_AXES];
 }
 
 static void set_info(struct mtdev *dev, int code,
@@ -156,10 +156,10 @@ int mtdev_has_mt_event(const struct mtdev *dev, int code)
                 return 0;
 
         ix = mtdev_abs2mt(code);
-        if (ix < 11)
+        if (ix < LEGACY_API_NUM_MT_AXES)
                 return dev->has_abs[ix];
         else
-                return dev->state->has_ext_abs[ix - 11];
+                return dev->state->has_ext_abs[ix - LEGACY_API_NUM_MT_AXES];
 }
 
 int mtdev_get_abs_minimum(const struct mtdev *dev, int code)
@@ -203,10 +203,10 @@ void mtdev_set_mt_event(struct mtdev *dev, int code, int value)
                 return;
 
         ix = mtdev_abs2mt(code);
-        if (ix < 11)
+        if (ix < LEGACY_API_NUM_MT_AXES)
                 dev->has_abs[ix] = value;
         else
-                dev->state->has_ext_abs[ix - 11] = value;
+                dev->state->has_ext_abs[ix - LEGACY_API_NUM_MT_AXES] = value;
 }
 
 void mtdev_set_abs_maximum(struct mtdev *dev, int code, int value)
diff --git a/src/common.h b/src/common.h
index 2ec8eb8..80a3d6e 100644
--- a/src/common.h
+++ b/src/common.h
@@ -87,6 +87,14 @@ static inline int bitcount(unsigned v)
 /* robust system ioctl calls */
 #define SYSCALL(call) while (((call) == -1) && (errno == EINTR))
 
+/* To be compatible to the original, non-opaque mtdev API, we can only use 11
+ * axes in the basic struct. Everything else is hidden in the state, see the
+ * use of dev->abs[idx] vs dev->state->ext_abs[idx]
+ *
+ * See MT_ABS_SIZE in include/mtdev.h
+ */
+#define LEGACY_API_NUM_MT_AXES 11
+
 /**
  * struct mtdev - represents an input MT device
  * @has_mtdata: true if the device has MT capabilities
@@ -105,9 +113,9 @@ static inline int bitcount(unsigned v)
 struct mtdev {
         int has_mtdata;
         int has_slot;
-        int has_abs[11];
+        int has_abs[LEGACY_API_NUM_MT_AXES];
         struct input_absinfo slot;
-        struct input_absinfo abs[11];
+        struct input_absinfo abs[LEGACY_API_NUM_MT_AXES];
         struct mtdev_state *state;
 };
 
diff --git a/src/state.h b/src/state.h
index 256858a..06e86ae 100644
--- a/src/state.h
+++ b/src/state.h
@@ -72,8 +72,8 @@ static inline void set_sval(struct mtdev_slot *slot, int ix, int value)
  */
 struct mtdev_state {
 
-        int has_ext_abs[MT_ABS_SIZE - 11];
-        struct input_absinfo ext_abs[MT_ABS_SIZE - 11];
+        int has_ext_abs[MT_ABS_SIZE - LEGACY_API_NUM_MT_AXES];
+        struct input_absinfo ext_abs[MT_ABS_SIZE - LEGACY_API_NUM_MT_AXES];
 
         struct mtdev_iobuf iobuf;
         struct mtdev_evbuf inbuf;