UBI: make gluebi a separate module

[Artem: re-worked the patch: made it release resources when the
module is unloaded, made it do module referencing, made it really
independent on UBI, tested it with the UBI test-suite which can
be found in ubi-2.6.git/tests/ubi-tests, re-named most of the
funcs/variables to get rid of the "ubi" word and make names
consistent.]

Signed-off-by: Dmitry Pervushin <dpervushin@embeddedalley.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

3 files changed, 295 insertions, 98 deletions

diff --git a/drivers/mtd/ubi/Kconfig b/drivers/mtd/ubi/Kconfig
index 3f063108e95f..b1cd7a1a2191 100644
--- a/drivers/mtd/ubi/Kconfig
+++ b/drivers/mtd/ubi/Kconfig
@@ -49,15 +49,16 @@ config MTD_UBI_BEB_RESERVE
           reserved. Leave the default value if unsure.
 
 config MTD_UBI_GLUEBI
-        bool "Emulate MTD devices"
+        tristate "MTD devices emulation driver (gluebi)"
         default n
         depends on MTD_UBI
         help
-           This option enables MTD devices emulation on top of UBI volumes: for
-           each UBI volumes an MTD device is created, and all I/O to this MTD
-           device is redirected to the UBI volume. This is handy to make
-           MTD-oriented software (like JFFS2) work on top of UBI. Do not enable
-           this if no legacy software will be used.
+           This option enables gluebi - an additional driver which emulates MTD
+           devices on top of UBI volumes: for each UBI volumes an MTD device is
+           created, and all I/O to this MTD device is redirected to the UBI
+           volume. This is handy to make MTD-oriented software (like JFFS2)
+           work on top of UBI. Do not enable this unless you use legacy
+           software.
 
 source "drivers/mtd/ubi/Kconfig.debug"
 endmenu
diff --git a/drivers/mtd/ubi/Makefile b/drivers/mtd/ubi/Makefile
index dd834e04151b..c9302a5452b0 100644
--- a/drivers/mtd/ubi/Makefile
+++ b/drivers/mtd/ubi/Makefile
@@ -4,4 +4,4 @@ ubi-y += vtbl.o vmt.o upd.o build.o cdev.o kapi.o eba.o io.o wl.o scan.o
 ubi-y += misc.o
 
 ubi-$(CONFIG_MTD_UBI_DEBUG) += debug.o
-ubi-$(CONFIG_MTD_UBI_GLUEBI) += gluebi.o
+obj-$(CONFIG_MTD_UBI_GLUEBI) += gluebi.o
diff --git a/drivers/mtd/ubi/gluebi.c b/drivers/mtd/ubi/gluebi.c
index 49cd55ade9c8..95aaac03f938 100644
--- a/drivers/mtd/ubi/gluebi.c
+++ b/drivers/mtd/ubi/gluebi.c
@@ -19,17 +19,71 @@
  */
 
 /*
- * This file includes implementation of fake MTD devices for each UBI volume.
- * This sounds strange, but it is in fact quite useful to make MTD-oriented
- * software (including all the legacy software) to work on top of UBI.
+ * This is a small driver which implements fake MTD devices on top of UBI
+ * volumes. This sounds strange, but it is in fact quite useful to make
+ * MTD-oriented software (including all the legacy software) work on top of
+ * UBI.
  *
  * Gluebi emulates MTD devices of "MTD_UBIVOLUME" type. Their minimal I/O unit
- * size (mtd->writesize) is equivalent to the UBI minimal I/O unit. The
+ * size (@mtd->writesize) is equivalent to the UBI minimal I/O unit. The
  * eraseblock size is equivalent to the logical eraseblock size of the volume.
  */
 
+#include <linux/err.h>
+#include <linux/list.h>
+#include <linux/sched.h>
 #include <linux/math64.h>
-#include "ubi.h"
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/mtd/ubi.h>
+#include <linux/mtd/mtd.h>
+#include "ubi-media.h"
+
+#define err_msg(fmt, ...)                                   \
+        printk(KERN_DEBUG "gluebi (pid %d): %s: " fmt "\n", \
+               current->pid, __func__, ##__VA_ARGS__)
+
+/**
+ * struct gluebi_device - a gluebi device description data structure.
+ * @mtd: emulated MTD device description object
+ * @refcnt: gluebi device reference count
+ * @desc: UBI volume descriptor
+ * @ubi_num: UBI device number this gluebi device works on
+ * @vol_id: ID of UBI volume this gluebi device works on
+ * @list: link in a list of gluebi devices
+ */
+struct gluebi_device {
+        struct mtd_info mtd;
+        int refcnt;
+        struct ubi_volume_desc *desc;
+        int ubi_num;
+        int vol_id;
+        struct list_head list;
+};
+
+/* List of all gluebi devices */
+static LIST_HEAD(gluebi_devices);
+static DEFINE_MUTEX(devices_mutex);
+
+/**
+ * find_gluebi_nolock - find a gluebi device.
+ * @ubi_num: UBI device number
+ * @vol_id: volume ID
+ *
+ * This function seraches for gluebi device corresponding to UBI device
+ * @ubi_num and UBI volume @vol_id. Returns the gluebi device description
+ * object in case of success and %NULL in case of failure. The caller has to
+ * have the &devices_mutex locked.
+ */
+static struct gluebi_device *find_gluebi_nolock(int ubi_num, int vol_id)
+{
+        struct gluebi_device *gluebi;
+
+        list_for_each_entry(gluebi, &gluebi_devices, list)
+                if (gluebi->ubi_num == ubi_num && gluebi->vol_id == vol_id)
+                        return gluebi;
+        return NULL;
+}
 
 /**
  * gluebi_get_device - get MTD device reference.
@@ -41,15 +95,18 @@
  */
 static int gluebi_get_device(struct mtd_info *mtd)
 {
-        struct ubi_volume *vol;
+        struct gluebi_device *gluebi;
+        int ubi_mode = UBI_READONLY;
 
-        vol = container_of(mtd, struct ubi_volume, gluebi_mtd);
+        if (!try_module_get(THIS_MODULE))
+                return -ENODEV;
 
-        /*
-         * We do not introduce locks for gluebi reference count because the
-         * get_device()/put_device() calls are already serialized at MTD.
-         */
-        if (vol->gluebi_refcount > 0) {
+        if (mtd->flags & MTD_WRITEABLE)
+                ubi_mode = UBI_READWRITE;
+
+        gluebi = container_of(mtd, struct gluebi_device, mtd);
+        mutex_lock(&devices_mutex);
+        if (gluebi->refcnt > 0) {
                 /*
                  * The MTD device is already referenced and this is just one
                  * more reference. MTD allows many users to open the same
@@ -58,7 +115,8 @@ static int gluebi_get_device(struct mtd_info *mtd)
                  * open the UBI volume again - just increase the reference
                  * counter and return.
                  */
-                vol->gluebi_refcount += 1;
+                gluebi->refcnt += 1;
+                mutex_unlock(&devices_mutex);
                 return 0;
         }
 
@@ -66,11 +124,15 @@ static int gluebi_get_device(struct mtd_info *mtd)
          * This is the first reference to this UBI volume via the MTD device
          * interface. Open the corresponding volume in read-write mode.
          */
-        vol->gluebi_desc = ubi_open_volume(vol->ubi->ubi_num, vol->vol_id,
-                                           UBI_READWRITE);
-        if (IS_ERR(vol->gluebi_desc))
-                return PTR_ERR(vol->gluebi_desc);
-        vol->gluebi_refcount += 1;
+        gluebi->desc = ubi_open_volume(gluebi->ubi_num, gluebi->vol_id,
+                                       ubi_mode);
+        if (IS_ERR(gluebi->desc)) {
+                mutex_unlock(&devices_mutex);
+                module_put(THIS_MODULE);
+                return PTR_ERR(gluebi->desc);
+        }
+        gluebi->refcnt += 1;
+        mutex_unlock(&devices_mutex);
         return 0;
 }
 
@@ -83,13 +145,15 @@ static int gluebi_get_device(struct mtd_info *mtd)
  */
 static void gluebi_put_device(struct mtd_info *mtd)
 {
-        struct ubi_volume *vol;
-
-        vol = container_of(mtd, struct ubi_volume, gluebi_mtd);
+        struct gluebi_device *gluebi;
+
+        gluebi = container_of(mtd, struct gluebi_device, mtd);