UBI: introduce attach ioctls

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

include/mtd/ubi-user.h

@@ -22,6 +22,21 @@
 #define __UBI_USER_H__
 
 /*
+ * UBI device creation (the same as MTD device attachment)
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * MTD devices may be attached using %UBI_IOCATT ioctl command of the UBI
+ * control device. The caller has to properly fill and pass
+ * &struct ubi_attach_req object - UBI will attach the MTD device specified in
+ * the request and return the newly created UBI device number as the ioctl
+ * return value.
+ *
+ * UBI device deletion (the same as MTD device detachment)
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * An UBI device maybe deleted with %UBI_IOCDET ioctl command of the UBI
+ * control device.
+ *
  * UBI volume creation
  * ~~~~~~~~~~~~~~~~~~~
  *
@@ -60,11 +75,12 @@
  */
 
 /*
- * When a new volume is created, users may either specify the volume number they
- * want to create or to let UBI automatically assign a volume number using this
- * constant.
+ * When a new UBI volume or UBI device is created, users may either specify the
+ * volume/device number they want to create or to let UBI automatically assign
+ * the number using these constants.
  */
 #define UBI_VOL_NUM_AUTO (-1)
+#define UBI_DEV_NUM_AUTO (-1)
 
 /* Maximum volume name length */
 #define UBI_MAX_VOLUME_NAME 127
@@ -80,6 +96,15 @@
 /* Re-size an UBI volume */
 #define UBI_IOCRSVOL _IOW(UBI_IOC_MAGIC, 2, struct ubi_rsvol_req)
 
+/* IOCTL commands of the UBI control character device */
+
+#define UBI_CTRL_IOC_MAGIC 'o'
+
+/* Attach an MTD device */
+#define UBI_IOCATT _IOW(UBI_CTRL_IOC_MAGIC, 64, struct ubi_attach_req)
+/* Detach an MTD device */
+#define UBI_IOCDET _IOW(UBI_CTRL_IOC_MAGIC, 65, int32_t)
+
 /* IOCTL commands of UBI volume character devices */
 
 #define UBI_VOL_IOC_MAGIC 'O'
@@ -89,6 +114,9 @@
 /* An eraseblock erasure command, used for debugging, disabled by default */
 #define UBI_IOCEBER _IOW(UBI_VOL_IOC_MAGIC, 1, int32_t)
 
+/* Maximum MTD device name length supported by UBI */
+#define MAX_UBI_MTD_NAME_LEN 127
+
 /*
  * UBI volume type constants.
  *
@@ -97,19 +125,55 @@
  */
 enum {
 	UBI_DYNAMIC_VOLUME = 3,
-	UBI_STATIC_VOLUME = 4
+	UBI_STATIC_VOLUME = 4,
+};
+
+/**
+ * struct ubi_attach_req - attach MTD device request.
+ * @ubi_num: UBI device number to create
+ * @mtd_num: MTD device number to attach
+ * @vid_hdr_offset: VID header offset (use defaults if %0)
+ * @padding: reserved for future, not used, has to be zeroed
+ *
+ * This data structure is used to specify MTD device UBI has to attach and the
+ * parameters it has to use. The number which should be assigned to the new UBI
+ * device is passed in @ubi_num. UBI may automatically assing the number if
+ * @UBI_DEV_NUM_AUTO is passed. In this case, the device number is returned in
+ * @ubi_num.
+ *
+ * Most applications should pass %0 in @vid_hdr_offset to make UBI use default
+ * offset of the VID header within physical eraseblocks. The default offset is
+ * the next min. I/O unit after the EC header. For example, it will be offset
+ * 512 in case of a 512 bytes page NAND flash with no sub-page support. Or
+ * it will be 512 in case of a 2KiB page NAND flash with 4 512-byte sub-pages.
+ *
+ * But in rare cases, if this optimizes things, the VID header may be placed to
+ * a different offset. For example, the boot-loader might do things faster if the
+ * VID header sits at the end of the first 2KiB NAND page with 4 sub-pages. As
+ * the boot-loader would not normally need to read EC headers (unless it needs
+ * UBI in RW mode), it might be faster to calculate ECC. This is weird example,
+ * but it real-life example. So, in this example, @vid_hdr_offer would be
+ * 2KiB-64 bytes = 1984. Note, that this position is not even 512-bytes
+ * aligned, which is OK, as UBI is clever enough to realize this is 4th sub-page
+ * of the first page and add needed padding.
+ */
+struct ubi_attach_req {
+	int32_t ubi_num;
+	int32_t mtd_num;
+	int32_t vid_hdr_offset;
+	uint8_t padding[12];
 };
 
 /**
  * struct ubi_mkvol_req - volume description data structure used in
- * volume creation requests.
+ *                        volume creation requests.
  * @vol_id: volume number
  * @alignment: volume alignment
  * @bytes: volume size in bytes
  * @vol_type: volume type (%UBI_DYNAMIC_VOLUME or %UBI_STATIC_VOLUME)
- * @padding1: reserved for future, not used
+ * @padding1: reserved for future, not used, has to be zeroed
  * @name_len: volume name length
- * @padding2: reserved for future, not used
+ * @padding2: reserved for future, not used, has to be zeroed
  * @name: volume name
  *
  * This structure is used by userspace programs when creating new volumes. The
@@ -139,7 +203,7 @@ struct ubi_mkvol_req {
 	int8_t padding1;
 	int16_t name_len;
 	int8_t padding2[4];
-	char name[UBI_MAX_VOLUME_NAME+1];
+	char name[UBI_MAX_VOLUME_NAME + 1];
 } __attribute__ ((packed));
 
 /**