block: allow disk to have extended device number

Now that disk and partition handlings are mostly unified, it's easy to
allow disk to have extended device number.  This patch makes
add_disk() use extended device number if disk->minors is zero.  Both
sd and ide-disk are updated to use this.

* sd_format_disk_name() is implemented which can generically determine
  the drive name.  This removes disk number restriction stemming from
  limited device names.

* If sd index goes over SD_MAX_DISKS (which can be increased now BTW),
  sd simply doesn't initialize minors letting block layer choose
  extended device number.

* If CONFIG_DEBUG_EXT_DEVT is set, both sd and ide-disk always set
  minors to 0 and use extended device numbers.

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

5 files changed, 82 insertions, 23 deletions

diff --git a/block/genhd.c b/block/genhd.c
index eedab5b4685b..d9de3e482d1e 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -478,14 +478,37 @@ static int exact_lock(dev_t devt, void *data)
  *
  * This function registers the partitioning information in @disk
  * with the kernel.
+ *
+ * FIXME: error handling
  */
 void add_disk(struct gendisk *disk)
 {
         struct backing_dev_info *bdi;
+        dev_t devt;
         int retval;
 
+        /* minors == 0 indicates to use ext devt from part0 and should
+         * be accompanied with EXT_DEVT flag.  Make sure all
+         * parameters make sense.
+         */
+        WARN_ON(disk->minors && !(disk->major || disk->first_minor));
+        WARN_ON(!disk->minors && !(disk->flags & GENHD_FL_EXT_DEVT));
+
         disk->flags |= GENHD_FL_UP;
-        disk_to_dev(disk)->devt = MKDEV(disk->major, disk->first_minor);
+
+        retval = blk_alloc_devt(&disk->part0, &devt);
+        if (retval) {
+                WARN_ON(1);
+                return;
+        }
+        disk_to_dev(disk)->devt = devt;
+
+        /* ->major and ->first_minor aren't supposed to be
+         * dereferenced from here on, but set them just in case.
+         */
+        disk->major = MAJOR(devt);
+        disk->first_minor = MINOR(devt);
+
         blk_register_region(disk_devt(disk), disk->minors, NULL,
                             exact_match, exact_lock, disk);
         register_disk(disk);
diff --git a/drivers/ide/ide-disk.c b/drivers/ide/ide-disk.c
index 29c8ae752683..33ea8c048717 100644
--- a/drivers/ide/ide-disk.c
+++ b/drivers/ide/ide-disk.c
@@ -44,7 +44,7 @@
 #if !defined(CONFIG_DEBUG_BLOCK_EXT_DEVT)
 #define IDE_DISK_MINORS         (1 << PARTN_BITS)
 #else
-#define IDE_DISK_MINORS         1
+#define IDE_DISK_MINORS         0
 #endif
 
 struct ide_disk_obj {
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 6598024531dd..bcb04b2a7676 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -89,7 +89,7 @@ MODULE_ALIAS_SCSI_DEVICE(TYPE_RBC);
 #if !defined(CONFIG_DEBUG_BLOCK_EXT_DEVT)
 #define SD_MINORS       16
 #else
-#define SD_MINORS       1
+#define SD_MINORS       0
 #endif
 
 static int  sd_revalidate_disk(struct gendisk *);
@@ -1770,6 +1770,52 @@ static int sd_revalidate_disk(struct gendisk *disk)
 }
 
 /**
+ *      sd_format_disk_name - format disk name
+ *      @prefix: name prefix - ie. "sd" for SCSI disks
+ *      @index: index of the disk to format name for
+ *      @buf: output buffer
+ *      @buflen: length of the output buffer
+ *
+ *      SCSI disk names starts at sda.  The 26th device is sdz and the
+ *      27th is sdaa.  The last one for two lettered suffix is sdzz
+ *      which is followed by sdaaa.
+ *
+ *      This is basically 26 base counting with one extra 'nil' entry
+ *      at the beggining from the second digit on and can be
+ *      determined using similar method as 26 base conversion with the
+ *      index shifted -1 after each digit is computed.
+ *
+ *      CONTEXT:
+ *      Don't care.
+ *
+ *      RETURNS:
+ *      0 on success, -errno on failure.
+ */
+static int sd_format_disk_name(char *prefix, int index, char *buf, int buflen)
+{
+        const int base = 'z' - 'a' + 1;
+        char *begin = buf + strlen(prefix);
+        char *end = buf + buflen;
+        char *p;
+        int unit;
+
+        p = end - 1;
+        *p = '\0';
+        unit = base;
+        do {
+                if (p == begin)
+                        return -EINVAL;
+                *--p = 'a' + (index % unit);
+                index = (index / unit) - 1;
+        } while (index >= 0);
+
+        memmove(begin, p, end - p);
+        memcpy(buf, prefix, strlen(prefix));
+
+        return 0;
+}
+
+/**
  *      sd_probe - called during driver initialization and whenever a
  *      new scsi device is attached to the system. It is called once
  *      for each scsi device (not just disks) present.
@@ -1821,8 +1867,8 @@ static int sd_probe(struct device *dev)
         if (error)
                 goto out_put;
 
-        error = -EBUSY;
-        if (index >= SD_MAX_DISKS)
+        error = sd_format_disk_name("sd", index, gd->disk_name, DISK_NAME_LEN);
+        if (error)
                 goto out_free_index;
 
         sdkp->device = sdp;
@@ -1849,24 +1895,12 @@ static int sd_probe(struct device *dev)
 
         get_device(&sdp->sdev_gendev);
 
-        gd->major = sd_major((index & 0xf0) >> 4);
-        gd->first_minor = ((index & 0xf) << 4) | (index & 0xfff00);
-        gd->minors = SD_MINORS;
-        gd->fops = &sd_fops;
-
-        if (index < 26) {
-                sprintf(gd->disk_name, "sd%c", 'a' + index % 26);
-        } else if (index < (26 + 1) * 26) {
-                sprintf(gd->disk_name, "sd%c%c",
-                        'a' + index / 26 - 1,'a' + index % 26);
-        } else {
-                const unsigned int m1 = (index / 26 - 1) / 26 - 1;
-                const unsigned int m2 = (index / 26 - 1) % 26;
-                const unsigned int m3 =  index % 26;
-                sprintf(gd->disk_name, "sd%c%c%c",
-                        'a' + m1, 'a' + m2, 'a' + m3);
+        if (index < SD_MAX_DISKS) {
+                gd->major = sd_major((index & 0xf0) >> 4);
+                gd->first_minor = ((index & 0xf) << 4) | (index & 0xfff00);
+                gd->minors = SD_MINORS;
         }
-
+        gd->fops = &sd_fops;
         gd->private_data = &sdkp->driver;
         gd->queue = sdkp->device->request_queue;
 
diff --git a/fs/partitions/check.c b/fs/partitions/check.c
index 772b2ed8d239..0e411603fdf5 100644
--- a/fs/partitions/check.c
+++ b/fs/partitions/check.c
@@ -593,6 +593,7 @@ void del_gendisk(struct gendisk *disk)
         disk_part_iter_exit(&piter);
 
         invalidate_partition(disk, 0);
+        blk_free_devt(disk_to_dev(disk)->devt);
         set_capacity(disk, 0);
         disk->flags &= ~GENHD_FL_UP;
         unlink_gendisk(disk);
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 04524c213de1..206cdf96c3a7 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -59,6 +59,7 @@ enum {
 };
 
 #define DISK_MAX_PARTS                  256
+#define DISK_NAME_LEN                   32
 
 #include <linux/major.h>
 #include <linux/device.h>
@@ -140,7 +141,7 @@ struct gendisk {
         int minors;                     /* maximum number of minors, =1 for
                                          * disks that can't be partitioned. */
 
-        char disk_name[32];             /* name of major driver */
+        char disk_name[DISK_NAME_LEN];  /* name of major driver */
 
         /* Array of pointers to partitions indexed by partno.
          * Protected with matching bdev lock but stat and other