block: don't depend on consecutive minor space

* Implement disk_devt() and part_devt() and use them to directly
  access devt instead of computing it from ->major and ->first_minor.

  Note that all references to ->major and ->first_minor outside of
  block layer is used to determine devt of the disk (the part0) and as
  ->major and ->first_minor will continue to represent devt for the
  disk, converting these users aren't strictly necessary.  However,
  convert them for consistency.

* Implement disk_max_parts() to avoid directly deferencing
  genhd->minors.

* Update bdget_disk() such that it doesn't assume consecutive minor
  space.

* Move devt computation from register_disk() to add_disk() and make it
  the only one (all other usages use the initially determined value).

These changes clean up the code and will help disk->part dereference
fix and extended block device numbers.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

16 files changed, 132 insertions, 67 deletions

diff --git a/block/genhd.c b/block/genhd.c
index dc9ad4c171e2..fa32d09fda24 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -186,13 +186,14 @@ void add_disk(struct gendisk *disk)
         int retval;
 
         disk->flags |= GENHD_FL_UP;
-        blk_register_region(MKDEV(disk->major, disk->first_minor),
-                            disk->minors, NULL, exact_match, exact_lock, disk);
+        disk->dev.devt = MKDEV(disk->major, disk->first_minor);
+        blk_register_region(disk_devt(disk), disk->minors, NULL,
+                            exact_match, exact_lock, disk);
         register_disk(disk);
         blk_register_queue(disk);
 
         bdi = &disk->queue->backing_dev_info;
-        bdi_register_dev(bdi, MKDEV(disk->major, disk->first_minor));
+        bdi_register_dev(bdi, disk_devt(disk));
         retval = sysfs_create_link(&disk->dev.kobj, &bdi->dev->kobj, "bdi");
         WARN_ON(retval);
 }
@@ -205,8 +206,7 @@ void unlink_gendisk(struct gendisk *disk)
         sysfs_remove_link(&disk->dev.kobj, "bdi");
         bdi_unregister(&disk->queue->backing_dev_info);
         blk_unregister_queue(disk);
-        blk_unregister_region(MKDEV(disk->major, disk->first_minor),
-                              disk->minors);
+        blk_unregister_region(disk_devt(disk), disk->minors);
 }
 
 /**
@@ -225,6 +225,38 @@ struct gendisk *get_gendisk(dev_t devt, int *partno)
         return  kobj ? dev_to_disk(dev) : NULL;
 }
 
+/**
+ * bdget_disk - do bdget() by gendisk and partition number
+ * @disk: gendisk of interest
+ * @partno: partition number
+ *
+ * Find partition @partno from @disk, do bdget() on it.
+ *
+ * CONTEXT:
+ * Don't care.
+ *
+ * RETURNS:
+ * Resulting block_device on success, NULL on failure.
+ */
+extern struct block_device *bdget_disk(struct gendisk *disk, int partno)
+{
+        dev_t devt = MKDEV(0, 0);
+
+        if (partno == 0)
+                devt = disk_devt(disk);
+        else {
+                struct hd_struct *part = disk->part[partno - 1];
+
+                if (part && part->nr_sects)
+                        devt = part_devt(part);
+        }
+
+        if (likely(devt != MKDEV(0, 0)))
+                return bdget(devt);
+        return NULL;
+}
+EXPORT_SYMBOL(bdget_disk);
+
 /*
  * print a full list of all partitions - intended for places where the root
  * filesystem can't be mounted and thus to give the victim some idea of what
@@ -255,7 +287,7 @@ void __init printk_all_partitions(void)
                  * option takes.
                  */
                 printk("%02x%02x %10llu %s",
-                       disk->major, disk->first_minor,
+                       MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)),
                        (unsigned long long)get_capacity(disk) >> 1,
                        disk_name(disk, 0, buf));
                 if (disk->driverfs_dev != NULL &&
@@ -266,15 +298,15 @@ void __init printk_all_partitions(void)
                         printk(" (driver?)\n");
 
                 /* now show the partitions */
-                for (n = 0; n < disk->minors - 1; ++n) {
-                        if (disk->part[n] == NULL)
-                                continue;
-                        if (disk->part[n]->nr_sects == 0)
+                for (n = 0; n < disk_max_parts(disk); ++n) {
+                        struct hd_struct *part = disk->part[n];
+
+                        if (!part || !part->nr_sects)
                                 continue;
                         printk("  %02x%02x %10llu %s\n",
-                               disk->major, n + 1 + disk->first_minor,
-                               (unsigned long long)disk->part[n]->nr_sects >> 1,
-                               disk_name(disk, n + 1, buf));
+                               MAJOR(part_devt(part)), MINOR(part_devt(part)),
+                               (unsigned long long)part->nr_sects >> 1,
+                               disk_name(disk, part->partno, buf));
                 }
         }
         class_dev_iter_exit(&iter);
@@ -343,26 +375,27 @@ static int show_partition(struct seq_file *seqf, void *v)
         char buf[BDEVNAME_SIZE];
 
         /* Don't show non-partitionable removeable devices or empty devices */
-        if (!get_capacity(sgp) ||
-                        (sgp->minors == 1 && (sgp->flags & GENHD_FL_REMOVABLE)))
+        if (!get_capacity(sgp) || (!disk_max_parts(sgp) &&
+                                   (sgp->flags & GENHD_FL_REMOVABLE)))
                 return 0;
         if (sgp->flags & GENHD_FL_SUPPRESS_PARTITION_INFO)
                 return 0;
 
         /* show the full disk and all non-0 size partitions of it */
         seq_printf(seqf, "%4d  %4d %10llu %s\n",
-                sgp->major, sgp->first_minor,
+                MAJOR(disk_devt(sgp)), MINOR(disk_devt(sgp)),
                 (unsigned long long)get_capacity(sgp) >> 1,
                 disk_name(sgp, 0, buf));
-        for (n = 0; n < sgp->minors - 1; n++) {
-                if (!sgp->part[n])
+        for (n = 0; n < disk_max_parts(sgp); n++) {
+                struct hd_struct *part = sgp->part[n];
+                if (!part)
                         continue;
-                if (sgp->part[n]->nr_sects == 0)
+                if (part->nr_sects == 0)
                         continue;
                 seq_printf(seqf, "%4d  %4d %10llu %s\n",
-                        sgp->major, n + 1 + sgp->first_minor,
-                        (unsigned long long)sgp->part[n]->nr_sects >> 1 ,
-                        disk_name(sgp, n + 1, buf));
+                           MAJOR(part_devt(part)), MINOR(part_devt(part)),
+                           (unsigned long long)part->nr_sects >> 1,
+                           disk_name(sgp, part->partno, buf));
         }
 
         return 0;
@@ -578,7 +611,8 @@ static int diskstats_show(struct seq_file *seqf, void *v)
         disk_round_stats(gp);
         preempt_enable();
         seq_printf(seqf, "%4d %4d %s %lu %lu %llu %u %lu %lu %llu %u %u %u %u\n",
-                gp->major, gp->first_minor, disk_name(gp, 0, buf),
+                MAJOR(disk_devt(gp)), MINOR(disk_devt(gp)),
+                disk_name(gp, 0, buf),
                 disk_stat_read(gp, ios[0]), disk_stat_read(gp, merges[0]),
                 (unsigned long long)disk_stat_read(gp, sectors[0]),
                 jiffies_to_msecs(disk_stat_read(gp, ticks[0])),
@@ -590,7 +624,7 @@ static int diskstats_show(struct seq_file *seqf, void *v)
                 jiffies_to_msecs(disk_stat_read(gp, time_in_queue)));
 
         /* now show all non-0 size partitions of it */
-        for (n = 0; n < gp->minors - 1; n++) {
+        for (n = 0; n < disk_max_parts(gp); n++) {
                 struct hd_struct *hd = gp->part[n];
 
                 if (!hd || !hd->nr_sects)
@@ -601,8 +635,8 @@ static int diskstats_show(struct seq_file *seqf, void *v)
                 preempt_enable();
                 seq_printf(seqf, "%4d %4d %s %lu %lu %llu "
                            "%u %lu %lu %llu %u %u %u %u\n",
-                           gp->major, n + gp->first_minor + 1,
-                           disk_name(gp, n + 1, buf),
+                           MAJOR(part_devt(hd)), MINOR(part_devt(hd)),
+                           disk_name(gp, hd->partno, buf),
                            part_stat_read(hd, ios[0]),
                            part_stat_read(hd, merges[0]),
                            (unsigned long long)part_stat_read(hd, sectors[0]),
@@ -661,11 +695,22 @@ dev_t blk_lookup_devt(const char *name, int partno)
         while ((dev = class_dev_iter_next(&iter))) {
                 struct gendisk *disk = dev_to_disk(dev);
 
-                if (!strcmp(dev->bus_id, name) && partno < disk->minors) {
-                        devt = MKDEV(MAJOR(dev->devt),
-                                     MINOR(dev->devt) + partno);
-                        break;
+                if (strcmp(dev->bus_id, name))
+                        continue;
+                if (partno < 0 || partno > disk_max_parts(disk))
+                        continue;
+
+                if (partno == 0)
+                        devt = disk_devt(disk);
+                else {
+                        struct hd_struct *part = disk->part[partno - 1];
+
+                        if (!part || !part->nr_sects)
+                                continue;
+
+                        devt = part_devt(part);
                 }
+                break;
         }
         class_dev_iter_exit(&iter);
         return devt;
@@ -755,7 +800,7 @@ void set_disk_ro(struct gendisk *disk, int flag)
 {
         int i;
         disk->policy = flag;
-        for (i = 0; i < disk->minors - 1; i++)
+        for (i = 0; i < disk_max_parts(disk); i++)
                 if (disk->part[i]) disk->part[i]->policy = flag;
 }
 
diff --git a/block/ioctl.c b/block/ioctl.c
index d77f5e280a6e..403f7d7e0c28 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -29,7 +29,7 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
         if (bdev != bdev->bd_contains)
                 return -EINVAL;
         partno = p.pno;
-        if (partno <= 0 || partno >= disk->minors)
+        if (partno <= 0 || partno > disk_max_parts(disk))
                 return -EINVAL;
         switch (a.op) {
                 case BLKPG_ADD_PARTITION:
@@ -47,7 +47,7 @@ static int blkpg_ioctl(struct block_device *bdev, struct blkpg_ioctl_arg __user
                         mutex_lock(&bdev->bd_mutex);
 
                         /* overlap? */
-                        for (i = 0; i < disk->minors - 1; i++) {
+                        for (i = 0; i < disk_max_parts(disk); i++) {
                                 struct hd_struct *s = disk->part[i];
 
                                 if (!s)
@@ -96,7 +96,7 @@ static int blkdev_reread_part(struct block_device *bdev)
         struct gendisk *disk = bdev->bd_disk;
         int res;
 
-        if (disk->minors == 1 || bdev != bdev->bd_contains)
+        if (!disk_max_parts(disk) || bdev != bdev->bd_contains)
                 return -EINVAL;
         if (!capable(CAP_SYS_ADMIN))
                 return -EACCES;
diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index 29b7a648cc6e..e1a90bbb4747 100644
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -2911,7 +2911,7 @@ static int pkt_setup_dev(dev_t dev, dev_t* pkt_dev)
         if (!disk->queue)
                 goto out_mem2;
 
-        pd->pkt_dev = MKDEV(disk->major, disk->first_minor);
+        pd->pkt_dev = MKDEV(pktdev_major, idx);
         ret = pkt_new_dev(pd, dev);
         if (ret)
                 goto out_new_dev;
diff --git a/drivers/block/ps3disk.c b/drivers/block/ps3disk.c
index 4b0d6c7f4c66..936466f62afd 100644
--- a/drivers/block/ps3disk.c
+++ b/drivers/block/ps3disk.c
@@ -541,7 +541,7 @@ static int ps3disk_remove(struct ps3_system_bus_device *_dev)
         struct ps3disk_private *priv = dev->sbd.core.driver_data;
 
         mutex_lock(&ps3disk_mask_mutex);
-        __clear_bit(priv->gendisk->first_minor / PS3DISK_MINORS,
+        __clear_bit(MINOR(disk_devt(priv->gendisk)) / PS3DISK_MINORS,
                     &ps3disk_mask);
         mutex_unlock(&ps3disk_mask_mutex);
         del_gendisk(priv->gendisk);
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 7ce1ac4baa6d..6af435b89867 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -661,10 +661,10 @@ void add_disk_randomness(struct gendisk *disk)
         if (!disk || !disk->random)
                 return;
         /* first major is 1, so we get >= 0x200 here */
-        DEBUG_ENT("disk event %d:%d\n", disk->major, disk->first_minor);
+        DEBUG_ENT("disk event %d:%d\n",
+                  MAJOR(disk_devt(disk)), MINOR(disk_devt(disk)));
 
-        add_timer_randomness(disk->random,
-                             0x100 + MKDEV(disk->major, disk->first_minor));
+        add_timer_randomness(disk->random, 0x100 + disk_devt(disk));
 }
 #endif
 
diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index b262c0042de3..c3de311117a1 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -426,7 +426,7 @@ static int list_devices(struct dm_ioctl *param, size_t param_size)
                                 old_nl->next = (uint32_t) ((void *) nl -
                                                            (void *) old_nl);
                         disk = dm_disk(hc->md);
-                        nl->dev = huge_encode_dev(MKDEV(disk->major, disk->first_minor));
+                        nl->dev = huge_encode_dev(disk_devt(disk));
                         nl->next = 0;
                         strcpy(nl->name, hc->name);
 
@@ -539,7 +539,7 @@ static int __dev_status(struct mapped_device *md, struct dm_ioctl *param)
         if (dm_suspended(md))
                 param->flags |= DM_SUSPEND_FLAG;
 
-        param->dev = huge_encode_dev(MKDEV(disk->major, disk->first_minor));
+        param->dev = huge_encode_dev(disk_devt(disk));
 
         /*
          * Yes, this will be out of date by the time it gets back
diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
index 4de90ab3968b..b745d8ac625b 100644
--- a/drivers/md/dm-stripe.c
+++ b/drivers/md/dm-stripe.c
@@ -284,8 +284,8 @@ static int stripe_end_io(struct dm_target *ti, struct bio *bio,
 
         memset(major_minor, 0, sizeof(major_minor));
         sprintf(major_minor, "%d:%d",
-                bio->bi_bdev->bd_disk->major,
-                bio->bi_bdev->bd_disk->first_minor);
+                MAJOR(disk_devt(bio->bi_bdev->bd_disk)),
+                MINOR(disk_devt(bio->bi_bdev->bd_disk)));
 
         /*
          * Test to see which stripe drive triggered the event
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index ace998ce59f6..a78caad29996 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1146,7 +1146,7 @@ static void unlock_fs(struct mapped_device *md);
 
 static void free_dev(struct mapped_device *md)
 {
-        int minor = md->disk->first_minor;
+        int minor = MINOR(disk_devt(md->disk));
 
         if (md->suspended_bdev) {
                 unlock_fs(md);
@@ -1267,7 +1267,7 @@ static struct mapped_device *dm_find_md(dev_t dev)
 
         md = idr_find(&_minor_idr, minor);
         if (md && (md == MINOR_ALLOCED ||
-                   (dm_disk(md)->first_minor != minor) ||
+                   (MINOR(disk_devt(dm_disk(md))) != minor) ||
                    test_bit(DMF_FREEING, &md->flags))) {
                 md = NULL;
                 goto out;
@@ -1318,7 +1318,8 @@ void dm_put(struct mapped_device *md)
 
         if (atomic_dec_and_lock(&md->holders, &_minor_lock)) {
                 map = dm_get_table(md);
-                idr_replace(&_minor_idr, MINOR_ALLOCED, dm_disk(md)->first_minor);
+                idr_replace(&_minor_idr, MINOR_ALLOCED,
+                            MINOR(disk_devt(dm_disk(md))));
                 set_bit(DMF_FREEING, &md->flags);
                 spin_unlock(&_minor_lock);
                 if (!dm_suspended(md)) {
diff --git a/drivers/memstick/core/mspro_block.c b/drivers/memstick/core/mspro_block.c
index d2d2318dafa4..82bf649ef138 100644
--- a/drivers/memstick/core/mspro_block.c
+++ b/drivers/memstick/core/mspro_block.c
@@ -197,7 +197,7 @@ static int mspro_block_bd_open(struct inode *inode, struct file *filp)
 static int mspro_block_disk_release(struct gendisk *disk)
 {
         struct mspro_block_data *msb = disk->private_data;
-        int disk_id = disk->first_minor >> MSPRO_BLOCK_PART_SHIFT;
+        int disk_id = MINOR(disk_devt(disk)) >> MSPRO_BLOCK_PART_SHIFT;
 
         mutex_lock(&mspro_block_disk_lock);
 
diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index ebc8b9d77613..97156b689e82 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -83,7 +83,7 @@ static void mmc_blk_put(struct mmc_blk_data *md)
         mutex_lock(&open_lock);
         md->usage--;
         if (md->usage == 0) {
-                int devidx = md->disk->first_minor >> MMC_SHIFT;
+                int devidx = MINOR(disk_devt(md->disk)) >> MMC_SHIFT;
                 __clear_bit(devidx, dev_use);
 
                 put_disk(md->disk);
diff --git a/drivers/s390/block/dasd_proc.c b/drivers/s390/block/dasd_proc.c
index 03c0e40a92ff..e3b5c4d3036e 100644
--- a/drivers/s390/block/dasd_proc.c
+++ b/drivers/s390/block/dasd_proc.c
@@ -76,7 +76,8 @@ dasd_devices_show(struct seq_file *m, void *v)
         /* Print kdev. */
         if (block->gdp)
                 seq_printf(m, " at (%3d:%6d)",
-                           block->gdp->major, block->gdp->first_minor);
+                           MAJOR(disk_devt(block->gdp)),
+                           MINOR(disk_devt(block->gdp)));
         else
                 seq_printf(m, "  at (???:??????)");
         /* Print device name. */
diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
index 711b3004b3e6..9481e4a3f76e 100644
--- a/drivers/s390/block/dcssblk.c
+++ b/drivers/s390/block/dcssblk.c
@@ -114,7 +114,7 @@ dcssblk_assign_free_minor(struct dcssblk_dev_info *dev_info)
                 found = 0;
                 // test if minor available
                 list_for_each_entry(entry, &dcssblk_devices, lh)
-                        if (minor == entry->gd->first_minor)
+                        if (minor == MINOR(disk_devt(entry->gd)))
                                 found++;
                 if (!found) break; // got unused minor
         }
@@ -397,7 +397,7 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
                 goto unload_seg;
         }
         sprintf(dev_info->gd->disk_name, "dcssblk%d",
-                dev_info->gd->first_minor);
+                MINOR(disk_devt(dev_info->gd)));
         list_add_tail(&dev_info->lh, &dcssblk_devices);
 
         if (!try_module_get(THIS_MODULE)) {
diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
index 27f5bfd1def3..8dbe3798d5fd 100644
--- a/drivers/scsi/sr.c
+++ b/drivers/scsi/sr.c
@@ -878,7 +878,7 @@ static void sr_kref_release(struct kref *kref)
         struct gendisk *disk = cd->disk;
 
         spin_lock(&sr_index_lock);
-        clear_bit(disk->first_minor, sr_index_bits);
+        clear_bit(MINOR(disk_devt(disk)), sr_index_bits);
         spin_unlock(&sr_index_lock);
 
         unregister_cdrom(&cd->cdi);
diff --git a/fs/block_dev.c b/fs/block_dev.c
index de0776cd7215..72e0a2887cb7 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -892,7 +892,7 @@ int check_disk_change(struct block_device *bdev)
 
         if (bdops->revalidate_disk)
                 bdops->revalidate_disk(bdev->bd_disk);
-        if (bdev->bd_disk->minors > 1)
+        if (disk_max_parts(bdev->bd_disk))
                 bdev->bd_invalidated = 1;
         return 1;
 }
diff --git a/fs/partitions/check.c b/fs/partitions/check.c
index b86aab1b0df6..e77fa144a07d 100644
--- a/fs/partitions/check.c
+++ b/fs/partitions/check.c
@@ -134,7 +134,11 @@ char *disk_name(struct gendisk *hd, int partno, char *buf)
 
 const char *bdevname(struct block_device *bdev, char *buf)
 {
-        int partno = MINOR(bdev->bd_dev) - bdev->bd_disk->first_minor;
+        int partno = 0;
+
+        if (bdev->bd_part)
+                partno = bdev->bd_part->partno;
+
         return disk_name(bdev->bd_disk, partno, buf);
 }
 
@@ -169,7 +173,7 @@ check_partition(struct gendisk *hd, struct block_device *bdev)
         if (isdigit(state->name[strlen(state->name)-1]))
                 sprintf(state->name, "p");
 
-        state->limit = hd->minors;
+        state->limit = disk_max_parts(hd) + 1;
         i = res = err = 0;
         while (!res && check_part[i]) {
                 memset(&state->parts, 0, sizeof(state->parts));
@@ -416,7 +420,6 @@ void register_disk(struct gendisk *disk)
         int err;
 
         disk->dev.parent = disk->driverfs_dev;
-        disk->dev.devt = MKDEV(disk->major, disk->first_minor);
 
         strlcpy(disk->dev.bus_id, disk->disk_name, BUS_ID_SIZE);
         /* ewww... some of these buggers have / in the name... */
@@ -440,7 +443,7 @@ void register_disk(struct gendisk *disk)
         disk_sysfs_add_subdirs(disk);
 
         /* No minors to use for partitions */
-        if (disk->minors == 1)
+        if (!disk_max_parts(disk))
                 goto exit;
 
         /* No such device (e.g., media were just removed) */
@@ -463,8 +466,8 @@ exit:
         kobject_uevent(&disk->dev.kobj, KOBJ_ADD);
 
         /* announce possible partitions */
-        for (i = 1; i < disk->minors; i++) {
-                p = disk->part[i-1];
+        for (i = 0; i < disk_max_parts(disk); i++) {
+                p = disk->part[i];
                 if (!p || !p->nr_sects)
                         continue;
                 kobject_uevent(&p->dev.kobj, KOBJ_ADD);
@@ -482,7 +485,7 @@ int rescan_partitions(struct gendisk *disk, struct block_device *bdev)
         if (res)
                 return res;
         bdev->bd_invalidated = 0;
-        for (p = 1; p < disk->minors; p++)
+        for (p = 1; p <= disk_max_parts(disk); p++)
                 delete_partition(disk, p);
         if (disk->fops->revalidate_disk)
                 disk->fops->revalidate_disk(disk);
@@ -545,7 +548,7 @@ void del_gendisk(struct gendisk *disk)
         int p;
 
         /* invalidate stuff */
-        for (p = disk->minors - 1; p > 0; p--) {
+        for (p = disk_max_parts(disk); p > 0; p--) {
                 invalidate_partition(disk, p);
                 delete_partition(disk, p);
         }
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index d1723c0a8600..0ff75329199c 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -111,10 +111,14 @@ struct hd_struct {
 #define GENHD_FL_FAIL                           64
 
 struct gendisk {
+        /* major, first_minor and minors are input parameters only,
+         * don't use directly.  Use disk_devt() and disk_max_parts().
+         */
         int major;                      /* major number of driver */
         int first_minor;
         int minors;                     /* maximum number of minors, =1 for
                                          * disks that can't be partitioned. */
+
         char disk_name[32];             /* name of major driver */
         struct hd_struct **part;        /* [indexed by minor - 1] */
         struct block_device_operations *fops;
@@ -152,6 +156,21 @@ static inline struct gendisk *part_to_disk(struct hd_struct *part)
         return NULL;
 }
 
+static inline int disk_max_parts(struct gendisk *disk)
+{
+        return disk->minors - 1;
+}
+
+static inline dev_t disk_devt(struct gendisk *disk)
+{
+        return disk->dev.devt;
+}
+
+static inline dev_t part_devt(struct hd_struct *part)
+{
+        return part->dev.devt;
+}
+
 /* 
  * Macros to operate on percpu disk statistics:
  *
@@ -163,7 +182,7 @@ static inline struct hd_struct *disk_map_sector(struct gendisk *gendiskp,
 {
         struct hd_struct *part;
         int i;
-        for (i = 0; i < gendiskp->minors - 1; i++) {
+        for (i = 0; i < disk_max_parts(gendiskp); i++) {
                 part = gendiskp->part[i];
                 if (part && part->start_sect <= sector
                     && sector < part->start_sect + part->nr_sects)
@@ -366,6 +385,7 @@ extern void add_disk(struct gendisk *disk);
 extern void del_gendisk(struct gendisk *gp);
 extern void unlink_gendisk(struct gendisk *gp);
 extern struct gendisk *get_gendisk(dev_t dev, int *partno);
+extern struct block_device *bdget_disk(struct gendisk *disk, int partno);
 
 extern void set_device_ro(struct block_device *bdev, int flag);
 extern void set_disk_ro(struct gendisk *disk, int flag);
@@ -553,11 +573,6 @@ extern void blk_register_region(dev_t devt, unsigned long range,
                         void *data);
 extern void blk_unregister_region(dev_t devt, unsigned long range);
 
-static inline struct block_device *bdget_disk(struct gendisk *disk, int partno)
-{
-        return bdget(MKDEV(disk->major, disk->first_minor) + partno);
-}
-
 #else /* CONFIG_BLOCK */
 
 static inline void printk_all_partitions(void) { }