[PATCH] switch sd numbering to idr

Switch sd.c device number allocation to use idr, this limits memory
usage for lowend setups and highend setups are only limited by the
available names now.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

drivers/scsi/sd.c

@@ -42,6 +42,7 @@
 #include <linux/genhd.h>
 #include <linux/hdreg.h>
 #include <linux/errno.h>
+#include <linux/idr.h>
 #include <linux/interrupt.h>
 #include <linux/init.h>
 #include <linux/blkdev.h>
@@ -62,12 +63,18 @@
 
 #include "scsi_logging.h"
 
-
 /*
- * Remaining dev_t-handling stuff
+ * More than enough for everybody ;)  The huge number of majors
+ * is a leftover from 16bit dev_t days, we don't really need that
+ * much numberspace.
  */
 #define SD_MAJORS	16
-#define SD_DISKS	32768	/* anything between 256 and 262144 */
+
+/*
+ * This is limited by the naming scheme enforced in sd_probe,
+ * add another character to it if you really need more disks.
+ */
+#define SD_MAX_DISKS	(((26 * 26) + 26 + 1) * 26)
 
 /*
  * Time out in seconds for disks and Magneto-opticals (which are slower).
@@ -96,8 +103,7 @@ struct scsi_disk {
 	unsigned	RCD : 1;	/* state of disk RCD bit, unused */
 };
 
-
-static unsigned long sd_index_bits[SD_DISKS / BITS_PER_LONG];
+static DEFINE_IDR(sd_index_idr);
 static spinlock_t sd_index_lock = SPIN_LOCK_UNLOCKED;
 
 /* This semaphore is used to mediate the 0->1 reference get in the
@@ -128,7 +134,8 @@ static struct scsi_driver sd_template = {
 	.init_command		= sd_init_command,
 };
 
-/* Device no to disk mapping:
+/*
+ * Device no to disk mapping:
  * 
  *       major         disc2     disc  p1
  *   |............|.............|....|....| <- dev_t
@@ -141,7 +148,6 @@ static struct scsi_driver sd_template = {
  * As we stay compatible with our numbering scheme, we can reuse 
  * the well-know SCSI majors 8, 65--71, 136--143.
  */
-
 static int sd_major(int major_idx)
 {
 	switch (major_idx) {
@@ -157,14 +163,6 @@ static int sd_major(int major_idx)
 	}
 }
 
-static unsigned int make_sd_dev(unsigned int sd_nr, unsigned int part)
-{
-	return  (part & 0xf) | ((sd_nr & 0xf) << 4) |
-		(sd_major((sd_nr & 0xf0) >> 4) << 20) | (sd_nr & 0xfff00);
-}
-
-/* reverse mapping dev -> (sd_nr, part) not currently needed */
-
 #define to_scsi_disk(obj) container_of(obj,struct scsi_disk,kref)
 
 static inline struct scsi_disk *scsi_disk(struct gendisk *disk)
@@ -1347,7 +1345,7 @@ static int sd_probe(struct device *dev)
 	struct scsi_disk *sdkp;
 	struct gendisk *gd;
 	u32 index;
-	int error, devno;
+	int error;
 
 	error = -ENODEV;
 	if ((sdp->type != TYPE_DISK) && (sdp->type != TYPE_MOD))
@@ -1364,25 +1362,21 @@ static int sd_probe(struct device *dev)
 	memset (sdkp, 0, sizeof(*sdkp));
 	kref_init(&sdkp->kref, scsi_disk_release);
 
-	/* Note: We can accomodate 64 partitions, but the genhd code
-	 * assumes partitions allocate consecutive minors, which they don't.
-	 * So for now stay with max 16 partitions and leave two spare bits. 
-	 * Later, we may change the genhd code and the alloc_disk() call
-	 * and the ->minors assignment here. 	KG, 2004-02-10
-	 */ 
 	gd = alloc_disk(16);
 	if (!gd)
 		goto out_free;
 
+	if (!idr_pre_get(&sd_index_idr, GFP_KERNEL))
+		goto out_put;
+
 	spin_lock(&sd_index_lock);
-	index = find_first_zero_bit(sd_index_bits, SD_DISKS);
-	if (index == SD_DISKS) {
-		spin_unlock(&sd_index_lock);
+	error = idr_get_new(&sd_index_idr, NULL, &index);
+	spin_unlock(&sd_index_lock);
+
+	if (index >= SD_MAX_DISKS)
 		error = -EBUSY;
+	if (error)
 		goto out_put;
-	}
-	__set_bit(index, sd_index_bits);
-	spin_unlock(&sd_index_lock);
 
 	sdkp->device = sdp;
 	sdkp->driver = &sd_template;
@@ -1397,15 +1391,14 @@ static int sd_probe(struct device *dev)
 			sdp->timeout = SD_MOD_TIMEOUT;
 	}
 
-	devno = make_sd_dev(index, 0);
-	gd->major = MAJOR(devno);
-	gd->first_minor = MINOR(devno);
+	gd->major = sd_major((index & 0xf0) >> 4);
+	gd->first_minor = ((index & 0xf) << 4) | (index & 0xfff00);
 	gd->minors = 16;
 	gd->fops = &sd_fops;
 
 	if (index < 26) {
 		sprintf(gd->disk_name, "sd%c", 'a' + index % 26);
-	} else if (index < (26*27)) {
+	} else if (index < (26 + 1) * 26) {
 		sprintf(gd->disk_name, "sd%c%c",
 			'a' + index / 26 - 1,'a' + index % 26);
 	} else {
@@ -1485,7 +1478,7 @@ static void scsi_disk_release(struct kref *kref)
 	struct gendisk *disk = sdkp->disk;
 	
 	spin_lock(&sd_index_lock);
-	clear_bit(sdkp->index, sd_index_bits);
+	idr_remove(&sd_index_idr, sdkp->index);
 	spin_unlock(&sd_index_lock);
 
 	disk->private_data = NULL;