[PATCH] Avoid EINVAL from XenStore

[Owen Smith <owen.smith@xxxxxxxxxx>]

XenStore Directory can return an empty string as the first element of
its buffer, which is converted into a 1 element array of (valid)
ANSI_STRINGs with length 0. When this 0 length string is passed to
XenStore Read, it attempts to read an invalid path (e.g. "~/drivers/")
which fails with EINVAL.
Add a check to skip 0 length strings in FdoClearDistribution.

Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>
---
 src/xenbus/fdo.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/xenbus/fdo.c b/src/xenbus/fdo.c
index 21de867..9c5decc 100644
--- a/src/xenbus/fdo.c
+++ b/src/xenbus/fdo.c
@@ -2606,6 +2606,11 @@ FdoClearDistribution(
     for (Index = 0; Distributions[Index].Buffer != NULL; Index++) {
         PANSI_STRING    Distribution = &Distributions[Index];
 
+        // If ~/drivers has no children, an empty string could be returned.
+        // Note: Distribution->Buffer is 1 CHAR of "\0"
+        if (Distribution[Index].Length == 0)
+            continue;
+
         status = XENBUS_STORE(Read,
                               &Fdo->StoreInterface,
                               NULL,
-- 
2.28.0.windows.1