[Xen-changelog] [xen-unstable] tools/examples/block better use of losetup -r

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir.fraser@xxxxxxxxxx>
# Date 1198076715 0
# Node ID 643ab64d12d5ce57e5f1e08f85ab4bb7fbc136ae
# Parent  b0c85bc56f9ef08a354499afea584c4b048068a3
tools/examples/block better use of losetup -r

Use losetup -r when the vbd is specified to be readonly, but only if
-r is supported (rather than always creating a writeable losetup
mapping if possible).

This was inspired by (but not derived from) a diff from the Fedora 8
patchset which uses -r iff the vbd is specified as readonly.  We need
to be cleverer upstream because not all systems have losetup -r.

Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 tools/examples/block |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diff -r b0c85bc56f9e -r 643ab64d12d5 tools/examples/block
--- a/tools/examples/block      Wed Dec 19 15:02:05 2007 +0000
+++ b/tools/examples/block      Wed Dec 19 15:05:15 2007 +0000
@@ -327,10 +327,13 @@ mount it read-write in a guest domain."
           fatal 'Failed to find an unused loop device'
         fi
 
-        status=$(losetup "$loopdev" "$file" || echo "failed")
-        if [ -n "$status" ]; then
-          do_or_die losetup -r "$loopdev" "$file"
-        fi
+        if LANG=C losetup -h 2>&1 | grep read-only >/dev/null
+        then
+          roflag="-$mode"; roflag="${roflag#-w}"
+        else
+          roflag=''
+        fi
+        do_or_die losetup $roflag "$loopdev" "$file"
         xenstore_write "$XENBUS_PATH/node" "$loopdev"
         write_dev "$loopdev"
         release_lock "block"

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