[PATCH 1/4] block: add function disk_name_format() into block core

[Ren Mingxin]

 According to 3e1a7ff8a0a7b948f2684930166954f9e8e776fe,
I copied function "sd_format_disk_name()" into block core with
the name of "disk_name_format()".

Signed-off-by: Ren Mingxin <renmx@xxxxxxxxxxxxxx>
---
 block/genhd.c         |   49 
+++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/genhd.h |    2 ++
 2 files changed, 51 insertions(+)

diff --git a/block/genhd.c b/block/genhd.c
index df9816e..10c04b6 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -357,6 +357,55 @@ void unregister_blkdev(unsigned int major, const 
char *name)

 EXPORT_SYMBOL(unregister_blkdev);

+/*
+ *     disk_name_format - 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
+ *
+ *     Take SCSI disks for example. 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 beginning 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.
+ */
+
+int disk_name_format(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;
+}
+
+EXPORT_SYMBOL(disk_name_format);
+
 static struct kobj_map *bdev_map;

 /**
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index e61d319..cd3d5e5 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -407,6 +407,8 @@ static inline void free_part_info(struct hd_struct 
*part)
 extern void part_round_stats(int cpu, struct hd_struct *part);

 /* block/genhd.c */
+extern int disk_name_format(char *prefix, int index, char *buf, int 
buflen);
+
 extern void add_disk(struct gendisk *disk);
 extern void del_gendisk(struct gendisk *gp);
 extern struct gendisk *get_gendisk(dev_t dev, int *partno);

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