[Xen-changelog] [xen-3.1-testing] Enable loopback disk image files on readonly nfs filesystem.

["Xen patchbot-3.1-testing" <patchbot-3.1-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1201186677 0
# Node ID 8fae9e400c4e156f2f216f338365dc053ddf58e7
# Parent  b8140d119ef8651e229c745b2478311154ff1892
Enable loopback disk image files on readonly nfs filesystem.

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 changeset:   16330:fbe7ed173314723f80f105e7e60fddd0bed77e5b
xen-unstable date:        Wed Nov 07 09:22:31 2007 +0000
---
 tools/examples/block |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletion(-)

diff -r b8140d119ef8 -r 8fae9e400c4e tools/examples/block
--- a/tools/examples/block      Thu Jan 24 14:53:46 2008 +0000
+++ b/tools/examples/block      Thu Jan 24 14:57:57 2008 +0000
@@ -367,7 +367,10 @@ mount it read-write in a guest domain."
           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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