[PATCH]Enable loopback disk image files on readonly nfs filesystem

[Zhignag Wang <zhigang.x.wang@oracle.com>]

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Hi all,

This small patch enables you to loopback disk image files on readonly nfs 
filesystem on some system.

When we losetup a file on readonly nfs filesystem, it fails with:
# losetup /dev/loop7 /data/vm/xen_el5_i386_para/system.raw
/data/vm/xen_el5_i386_para/system.raw: Permission denied

New version of losetup has add a "-r" option for readonly loop, which Linux 
kernel has supported for a long time. Some distribution (EL5 update, Fedora 8, 
etc.) have shipped it. This patch benefit this option while doesn't break the 
old versions of losetup.

Signed-off-by: Zhigang Wang <zhigang.x.wang@oracle.com>

regards,

zhigang

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--- xen-unstable/tools/examples/block.orig	2007-11-06 20:01:53.000000000 -0800
+++ xen-unstable/tools/examples/block	2007-11-06 20:03:14.000000000 -0800
@@ -326,7 +326,10 @@
           fatal 'Failed to find an unused loop device'
         fi
 
-        do_or_die losetup "$loopdev" "$file"
+        status=$(losetup "$loopdev" "$file" || echo "failed")
+        if [ -n "$status" ]; then
+          do_or_die losetup -r "$loopdev" "$file"
+        fi
         xenstore_write "$XENBUS_PATH/node" "$loopdev"
         write_dev "$loopdev"
         release_lock "block"

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