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

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@xxxxxxxxxx>


--- xen-unstable/tools/examples/block.orig      2007-11-06 20:01:53.000000000 
+++ 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'
-        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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