Add method to get kernel driver version

Add a method to allow the userspace library to obtain the API version
of the kernel driver.  This allows us to automatically adjust to
changes in the API and fail cleanly when we detect an incompatibility.

2 files changed, 41 insertions, 0 deletions

diff --git a/bmm_lib.c b/bmm_lib.c
index e6ba3e9..f9d8e69 100644
--- a/bmm_lib.c
+++ b/bmm_lib.c
@@ -30,8 +30,37 @@
 #define pr_debug(fmt, arg...) do { } while(0)
 #endif
 
+#define API_FEAT_MIN		0x0000
+#define API_COMP_MAX		0x0000
+#define API_FEAT(x)		((x) >> 16)
+#define API_COMP(x)		((x) & 0xffff)
+
+static unsigned bmm_api;
 static int bmm_fd = -1;
 
+static int bmm_get_api_version(void)
+{
+	ioctl_arg_t io;
+
+	/* Get the BMM API version */
+	io.input = 0;
+	io.arg = 0;
+	io.output = 0;
+	if (ioctl(bmm_fd, BMM_API_VERSION, &io) == 0 &&
+	    io.input == 0xdeaddead && io.arg == 0xfacebeef)
+		bmm_api = io.output;
+	else
+		bmm_api = 0;
+
+	pr_debug("BMM API version %08x\n", bmm_api);
+
+	if (API_FEAT(bmm_api) < API_FEAT_MIN ||
+	    API_COMP(bmm_api) > API_COMP_MAX)
+		return -1;
+
+	return 0;
+}
+
 int bmm_init()
 {
         /* attempt to open the BMM driver */
@@ -39,9 +68,20 @@ int bmm_init()
 		bmm_fd = open(BMM_DEVICE_FILE, O_RDWR | O_CLOEXEC);
 
 		pr_debug("BMM device fd: %d\n", bmm_fd);
+		if (bmm_fd < 0)
+			goto err_open;
+
+		if (bmm_get_api_version() < 0)
+			goto err_api;
 	}
 
 	return bmm_fd;
+
+ err_api:
+	close(bmm_fd);
+	bmm_fd = -1;
+ err_open:
+	return bmm_fd;
 }
 
 void bmm_exit()
diff --git a/bmm_lib_priv.h b/bmm_lib_priv.h
index 3ae48f2..41cb680 100644
--- a/bmm_lib_priv.h
+++ b/bmm_lib_priv.h
@@ -41,6 +41,7 @@ typedef struct {
 #define BMM_GET_KERN_PHYS_ADDR	_IOWR(BMEM_IOCTL_MAGIC, 15, ioctl_arg_t)
 #define BMM_SYNC_USER		_IOWR(BMEM_IOCTL_MAGIC, 16, ioctl_arg_t)
 #define BMM_MALLOC_ALIGNED	_IOWR(BMEM_IOCTL_MAGIC, 17, ioctl_arg_t)
+#define BMM_API_VERSION		_IOWR(BMEM_IOCTL_MAGIC, 18, ioctl_arg_t)
 
 #define BMM_DEVICE_FILE	"/dev/bmm"