mdadm --detail showing annoying device

[Stephane Bunel <stephane.bunel@forumdesimages.fr>]

Hi,

I'm a newbie in the mdadm world. I defined some udev rules to make disk 
staticly named according to the bus/host/target. I.e. /dev/sda become 
/dev/raid_disk0. So nothing very special with that, it's just a convenient way 
to assign disk name to it's physical location.

#ls -la /dev/raid*
brw-rw---- 1 root disk 8,  0 2009-10-16 18:12 /dev/raid_disk0
brw-rw---- 1 root disk 8, 16 2009-10-16 18:12 /dev/raid_disk1

A RAID1 (/dev/md0) is assembled over this two disk.
When looking for detailed information, mdadm show annoying device name in 
place of /dev/raid_disk*:

---8x---
#mdadm --detail /dev/md0
/dev/md0:
         Version : 0.90
   Creation Time : Tue Oct 13 12:53:54 2009
      Raid Level : raid1
      Array Size : 488386496 (465.76 GiB 500.11 GB)
   Used Dev Size : 488386496 (465.76 GiB 500.11 GB)
    Raid Devices : 2
   Total Devices : 2
Preferred Minor : 0
     Persistence : Superblock is persistent

     Update Time : Wed Oct 21 15:16:09 2009
           State : clean
  Active Devices : 2
Working Devices : 2
  Failed Devices : 0
   Spare Devices : 0

            UUID : 3fea95a0:e1b8a341:3b119117:e416f62b
          Events : 0.1526

     Number   Major   Minor   RaidDevice State
        0       8        0        0      active sync   /dev/char/21:0
        1       8       16        1      active sync   /dev/char/21:1
---8x---


Looking in the source code of mdadm I found that the device name selection 
rule is (too) simply: select the shortest name in case of multiple 
possibility. So '/dev/char/21:0' being shorter than '/dev/raid_disk0', mdadm 
display '/dev/char...'. It's annoying for me to see a CHAR (/dev/char/...) 
device to represent a hard disk (wich is is a block device of course). The 
purpose of the following patch is to handle the directory part to always 
prefere the name that is closer to /dev. In case of equality, the shorter name 
wins.


---8x---
#./mdadm --detail /dev/md0
/dev/md0:
         Version : 0.90
   Creation Time : Tue Oct 13 12:53:54 2009
      Raid Level : raid1
      Array Size : 488386496 (465.76 GiB 500.11 GB)
   Used Dev Size : 488386496 (465.76 GiB 500.11 GB)
    Raid Devices : 2
   Total Devices : 2
Preferred Minor : 0
     Persistence : Superblock is persistent

     Update Time : Wed Oct 21 15:30:34 2009
           State : clean
  Active Devices : 2
Working Devices : 2
  Failed Devices : 0
   Spare Devices : 0

            UUID : 3fea95a0:e1b8a341:3b119117:e416f62b
          Events : 0.1526

     Number   Major   Minor   RaidDevice State
        0       8        0        0      active sync   /dev/raid_disk0
        1       8       16        1      active sync   /dev/raid_disk1
---8x---


Fell free to refactor the code. The last time I wrote C code I still had hair 
on my head ;-)


---8x---
--- /var/tmp/mdadm_snapshot/util.c    2009-10-20 04:50:23.000000000 +0200
+++ /var/tmp/mdadm_dirlevel/util.c    2009-10-20 13:13:32.000000000 +0200
@@ -507,6 +507,38 @@
  #endif /* HAVE_FTW */
  #endif /* HAVE_NFTW */

+char *select_by_directory_level(char *current, char *registered)
+{
+        unsigned int current_level = 0;
+        unsigned int registered_level = 0;
+
+        unsigned int level(char *pathname)
+        {
+                unsigned int count = 0;
+                char *p = pathname;
+
+                while ( (p = strchr( p, '/' )) ) {
+                        count++;
+                        p++;
+                }
+
+                return( count );
+        }
+
+        current_level = level( current );
+        registered_level = level( registered );
+
+        if (  current_level < registered_level )
+                return current;
+
+        if ( current_level == registered_level )
+                if ( strlen( strrchr( current, '/')) <
+                     strlen( strrchr( registered,'/')) )
+                        return current;
+
+        return registered;
+}
+
  /*
   * Find a block device with the right major/minor number.
   * If we find multiple names, choose the shortest.
@@ -544,14 +576,18 @@
          if (p->major == major &&
              p->minor == minor) {
              if (strncmp(p->name, "/dev/md/",8) == 0) {
-                if (preferred == NULL ||
-                    strlen(p->name) < strlen(preferred))
-                    preferred = p->name;
-            } else {
-                if (regular == NULL ||
-                    strlen(p->name) < strlen(regular))
-                    regular = p->name;
-            }
+                                if (preferred == NULL)
+                                        preferred = p->name;
+                                else
+                                        preferred =
select_by_directory_level(
+                                                        p->name,
preferred );
+                        } else {
+                                if (regular == NULL )
+                                        regular = p->name;
+                                else
+                                        regular = select_by_directory_level(
+                                                        p->name, regular );
+                        }
          }
      if (!regular && !preferred && !did_check) {
          devlist_ready = 0;
---8x---



Stéphane Bunel.


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