Xen devel - Nov 2005 - [patch] loopback block device confliction is fixed.

Hi.

I found cause of problem that loopback devices is not connect when more
than two loopback block devices is used.
The cause is setup these loopback block devices concurrently, so that
these devices indicate same loopback devices.
(show log file ... message.log)

I attach tentative patch for this problem. (block.patch)
This patch is that searching is stopped if free loop back device is
found.
Process is very fast, so that in my environments, confliction is not
observed.

I think that good resolution is provide lock mechanism.

Thank you.


diff -r 243265ade404 tools/examples/block
--- a/tools/examples/block      Mon Nov 28 17:22:02 2005
+++ b/tools/examples/block      Wed Nov 30 12:35:35 2005
@@ -238,6 +238,7 @@
             if [ "$loopdev" == '''' ]
             then
               loopdev="$dev"
+             break
             fi
           fi
         done



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Hi.

Sorry.
My past patch cannot solve confliction problems, but can decrease its
occurrence.
And, when loopback devices mounted become fragment, sharing cannot
checked for all loopback devices.

Therefore, I create new patch.
This patch is to stock candidate devices at first stage ( searching and
sharing check stage), and to try to assign loopback devices within
candidate devise gradually.

Thanks

Satoshi UCHIDA

 
diff -r 243265ade404 tools/examples/block
--- a/tools/examples/block      Mon Nov 28 17:22:02 2005
+++ b/tools/examples/block      Wed Nov 30 15:08:26 2005
@@ -202,7 +202,7 @@
 mount it read-write in a guest domain."
         fi
 
-        loopdev=''''
+        loopdevs=''''
 
        for dev in /dev/loop*
         do
@@ -235,26 +235,26 @@
             # $dev is not in use, so we''ll remember it for use later;
we want
             # to finish the sharing check first.
             
-            if [ "$loopdev" == '''' ]
-            then
-              loopdev="$dev"
-            fi
+            loopdevs="$loopdevs $dev"
           fi
         done
 
-        if [ "$loopdev" == '''' ]
+        if [ "$loopdevs" == '''' ]
         then
           fatal ''Failed to find an unused loop device''
         fi
 
-        if losetup "$loopdev" "$file"
-        then
-          xenstore_write "$XENBUS_PATH/node" "$loopdev"
-          write_dev "$loopdev"
-          exit 0
-        else
-          fatal "losetup $loopdev $file failed"
-        fi
+       for loopdev in $loopdevs
+       do
+         if losetup "$loopdev" "$file"
+         then
+            xenstore_write "$XENBUS_PATH/node" "$loopdev"
+            write_dev "$loopdev"
+            exit 0
+          fi
+        done
+
+       fatal "losetup $loopdev $file failed"
        ;;
     esac
     ;;


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On Wed, Nov 30, 2005 at 12:04:36PM +0900, Satoshi Uchida wrote:
> Hi.
> 
> I found cause of problem that loopback devices is not connect when more
> than two loopback block devices is used.
> The cause is setup these loopback block devices concurrently, so that
> these devices indicate same loopback devices.
> (show log file ... message.log)
> 
> I attach tentative patch for this problem. (block.patch)
> This patch is that searching is stopped if free loop back device is
> found.
> Process is very fast, so that in my environments, confliction is not
> observed.
> 
> I think that good resolution is provide lock mechanism.
Thanks for your analysis and your tentative patch.  You were right that a
better fix was to provide a lock mechanism, and that''s what
I''ve done.

Cheers,

Ewan.

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