Especially PV device drivers often need to read multiple Xenstore
nodes from a common directory. Add support for reading a string or an
unsigned value by specifying the directory and the node.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
---
V2:
- check sscanf() return value (Samuel Thibault)
---
 include/xenbus.h |  6 ++++++
 xenbus.c         | 40 +++++++++++++++++++++++++++++++++++++---
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/include/xenbus.h b/include/xenbus.h
index 3871f358..c0fc0ac5 100644
--- a/include/xenbus.h
+++ b/include/xenbus.h
@@ -108,6 +108,12 @@ int xenbus_read_integer(const char *path);
  * read and parsing were successful, 0 if not */
 int xenbus_read_uuid(const char* path, unsigned char uuid[16]);
 
+/* Support functions for reading values from directory/node tuple. */
+char *xenbus_read_string(xenbus_transaction_t xbt, const char *dir,
+                         const char *node, char **value);
+char *xenbus_read_unsigned(xenbus_transaction_t xbt, const char *dir,
+                           const char *node, unsigned int *value);
+
 /* Contraction of snprintf and xenbus_write(path/node). */
 char* xenbus_printf(xenbus_transaction_t xbt,
                                   const char* node, const char* path,
diff --git a/xenbus.c b/xenbus.c
index 81e9b65d..923e8181 100644
--- a/xenbus.c
+++ b/xenbus.c
@@ -936,16 +936,21 @@ int xenbus_read_uuid(const char *path, unsigned char uuid[16])
     return 1;
 }
 
+#define BUFFER_SIZE 256
+static void xenbus_build_path(const char *dir, const char *node, char *res)
+{
+    BUG_ON(strlen(dir) + strlen(node) + 1 >= BUFFER_SIZE);
+    sprintf(res,"%s/%s", dir, node);
+}
+
 char *xenbus_printf(xenbus_transaction_t xbt, const char* node,
                     const char* path, const char* fmt, ...)
 {
-#define BUFFER_SIZE 256
     char fullpath[BUFFER_SIZE];
     char val[BUFFER_SIZE];
     va_list args;
 
-    BUG_ON(strlen(node) + strlen(path) + 1 >= BUFFER_SIZE);
-    sprintf(fullpath,"%s/%s", node, path);
+    xenbus_build_path(node, path, fullpath);
     va_start(args, fmt);
     vsprintf(val, fmt, args);
     va_end(args);
@@ -964,6 +969,35 @@ domid_t xenbus_get_self_id(void)
     return ret;
 }
 
+char *xenbus_read_string(xenbus_transaction_t xbt, const char *dir,
+                         const char *node, char **value)
+{
+    char path[BUFFER_SIZE];
+
+    xenbus_build_path(dir, node, path);
+
+    return xenbus_read(xbt, path, value);
+}
+
+char *xenbus_read_unsigned(xenbus_transaction_t xbt, const char *dir,
+                           const char *node, unsigned int *value)
+{
+    char path[BUFFER_SIZE];
+    char *msg;
+    char *str;
+
+    xenbus_build_path(dir, node, path);
+    msg = xenbus_read(xbt, path, &str);
+    if ( msg )
+        return msg;
+
+    if ( sscanf(str, "%u", value) != 1 )
+        msg = strdup("EINVAL");
+    free(str);
+
+    return msg;
+}
+
 /*
  * Local variables:
  * mode: C
-- 
2.35.3