[Xen-changelog] [xen-unstable] libxl: fix transaction leak in logdirty error path

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
# Date 1343234357 -3600
# Node ID b0d31b81aa588ef712cfbc6c8e4531082b2e26cd
# Parent  e37bd3d6f769a9604adacbef747d9dff9705e69a
libxl: fix transaction leak in logdirty error path

libxl__domain_suspend_common_switch_qemu_logdirty would leak t if
there was an error.  Fix this.

Also, document the intended usage for libxl__xs_transaction_* in the
doc comment in libxl_internal.h.

Reported-by: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Acked-by: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Committed-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---


diff -r e37bd3d6f769 -r b0d31b81aa58 tools/libxl/libxl_dom.c
--- a/tools/libxl/libxl_dom.c   Wed Jul 25 17:39:16 2012 +0100
+++ b/tools/libxl/libxl_dom.c   Wed Jul 25 17:39:17 2012 +0100
@@ -628,6 +628,7 @@ void libxl__domain_suspend_common_switch
 
  out:
     LOG(ERROR,"logdirty switch failed (rc=%d), aborting suspend",rc);
+    libxl__xs_transaction_abort(gc, &t);
     switch_logdirty_done(egc,dss,-1);
 }
 
diff -r e37bd3d6f769 -r b0d31b81aa58 tools/libxl/libxl_internal.h
--- a/tools/libxl/libxl_internal.h      Wed Jul 25 17:39:16 2012 +0100
+++ b/tools/libxl/libxl_internal.h      Wed Jul 25 17:39:17 2012 +0100
@@ -550,6 +550,42 @@ int libxl__xs_rm_checked(libxl__gc *gc, 
  *   +1  commit conflict; transaction has been destroyed and caller
  *        must go round again (call _start again and retry)
  *    0  committed successfully
+ *
+ * The intended usage pattern looks like this:
+ *    int some_function()
+ *    {
+ *        int rc;
+ *        xs_transaction_t t = 0;
+ *        // other initialisations
+ *
+ *        // do whatever you need to do before the xenstore stuff
+ *        // errors?  set rc and goto out.
+ *
+ *        for (;;) {
+ *            rc = libxl__xs_transaction_start(gc, &t);
+ *            if (rc) goto out;
+ *
+ *            // do your work here, including all xenstore reads and writes
+ *            // libxl__xs_*_checked are useful; pass them t.
+ *            // errors?  set rc and goto out.
+ *
+ *            rc = libxl__xs_transaction_commit(gc, &t);
+ *            if (!rc) break;
+ *            if (rc<0) goto out;
+ *        }
+ *
+ *        // now the xenstore transaction succeeded
+ *        // do whatever else you need to do
+ *        // errors?  set rc and goto out.
+ *
+ *        return something;
+ *
+ *     out:
+ *        // other cleanups
+ *        libxl__xs_transaction_abort(gc, &t);
+ *        // other cleanups
+ *        return rc;
+ *    }
  */
 int libxl__xs_transaction_start(libxl__gc *gc, xs_transaction_t *t);
 int libxl__xs_transaction_commit(libxl__gc *gc, xs_transaction_t *t);

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