Block script unsafe when starting multiple devices in parallel

[Nathan March <nathan@gt.net>]

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Hi Guys,

Ran into an issue where losetup was failing, added some logging to it's 
executions to see (first #'s are parent pid / pid):

32435 / 32438 - losetup -f
32436 / 32439 - losetup -f
32435 / 32438 -  Exit code: 0
32435 / 32438 -  Output: /dev/loop/10
32436 / 32439 -  Exit code: 0
32436 / 32439 -  Output: /dev/loop/10
32128 / 32451 - losetup /dev/loop/10 /mnt/xenDisks2/nathanxen2/backup_tmp
31934 / 32452 - losetup /dev/loop/10 /mnt/xenDisks1/nathanxen2/swap

Sometime's losetup seems to be stuck waiting on something else and since 
multiple block devices are brought up in parallel, the block script 
tries to use the same name for multiple loopback devices.

Fix for this is pretty straightforward - should just be letting losetup 
figure out the device names itself, patch is attached.

- Nathan

-- 
Nathan March<nathan@gt.net>
Gossamer Threads Inc. http://www.gossamer-threads.com/
Tel: (604) 687-5804 Fax: (604) 687-5806


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--- block.orig	2011-08-30 10:17:05.663106731 -0700
+++ block	2011-08-30 10:18:49.742946473 -0700
@@ -292,12 +292,12 @@
           done
         fi
 
-        loopdev=$(losetup -f 2>/dev/null || find_free_loopback_dev)
-        if [ "$loopdev" = '' ]
-        then
-          release_lock "block"
-          fatal 'Failed to find an unused loop device'
-        fi
+        #loopdev=$(losetup -f 2>/dev/null || find_free_loopback_dev)
+        #if [ "$loopdev" = '' ]
+        #then
+        #  release_lock "block"
+        #  fatal 'Failed to find an unused loop device'
+        #fi
 
         if LANG=C losetup -h 2>&1 | grep read-only >/dev/null
         then
@@ -305,7 +305,12 @@
         else
           roflag=''
         fi
-        do_or_die losetup $roflag "$loopdev" "$file"
+
+        loopdev=$(losetup -f "$file" --show)
+        if [[ $? -ne 0 ]]; then
+            fatal "Unable to bring up $file - $loopdev"
+        fi;
+        #do_or_die losetup $roflag "$loopdev" "$file"
         xenstore_write "$XENBUS_PATH/node" "$loopdev"
         write_dev "$loopdev"
         release_lock "block"

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