libxl: Provide libxl__backendpath_parse_domid

Multiple places in libxl need to figure out the backend domid of a
device.  This can be discovered easily by looking at the backend path,
which always starts /local/domain/$backend_domid/.

There are no call sites yet.

This is part of XSA-175.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>

diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index b4bd005b4f888381468ec89e94952105ec84794f..9f115c628c0258fb31b608cc6de02f09daba60d1 100644 (file)
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -298,6 +298,21 @@ static int disk_try_backend(disk_try_backend_args *a,
     return 0;
 }
 
+int libxl__backendpath_parse_domid(libxl__gc *gc, const char *be_path,
+                                   libxl_domid *domid_out) {
+    int r;
+    unsigned int domid_sc;
+    char delim_sc;
+
+    r = sscanf(be_path, "/local/domain/%u%c", &domid_sc, &delim_sc);
+    if (!(r==2 && delim_sc=='/')) {
+        LOG(ERROR, "internal error: backend path %s unparseable!", be_path);
+        return ERROR_FAIL;
+    }
+    *domid_out = domid_sc;
+    return 0;
+}
+
 int libxl__device_disk_set_backend(libxl__gc *gc, libxl_device_disk *disk) {
     libxl_disk_backend ok;
     disk_try_backend_args a;

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index a4a461330f6696fc8481cf49a7ec76de31e623f9..d8b877b8a4e12d62b7161504f0cf0315d9f1b8e6 100644 (file)
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -702,6 +702,8 @@ _hidden char **libxl__xs_directory(libxl__gc *gc, xs_transaction_t t,
    /* On error: returns NULL, sets errno (no logging) */
 _hidden char *libxl__xs_libxl_path(libxl__gc *gc, uint32_t domid);
 
+_hidden int libxl__backendpath_parse_domid(libxl__gc *gc, const char *be_path,
+                                           libxl_domid *domid_out);
 
 /*----- "checked" xenstore access functions -----*/
 /* Each of these functions will check that it succeeded; if it