xen/hypfs: switch write function handles to const

The node specific write functions take a void user address handle as
parameter. As a write won't change the user memory use a const_void
handle instead.

This requires a new macro for casting a guest handle to a const type.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/common/hypfs.c

@@ -344,7 +344,8 @@ static int hypfs_read(const struct hypfs_entry *entry,
 }
 
 int hypfs_write_leaf(struct hypfs_entry_leaf *leaf,
-                     XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned int ulen)
+                     XEN_GUEST_HANDLE_PARAM(const_void) uaddr,
+                     unsigned int ulen)
 {
     char *buf;
     int ret;
@@ -384,7 +385,8 @@ int hypfs_write_leaf(struct hypfs_entry_leaf *leaf,
 }
 
 int hypfs_write_bool(struct hypfs_entry_leaf *leaf,
-                     XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned int ulen)
+                     XEN_GUEST_HANDLE_PARAM(const_void) uaddr,
+                     unsigned int ulen)
 {
     bool buf;
 
@@ -405,7 +407,8 @@ int hypfs_write_bool(struct hypfs_entry_leaf *leaf,
 }
 
 int hypfs_write_custom(struct hypfs_entry_leaf *leaf,
-                       XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned int ulen)
+                       XEN_GUEST_HANDLE_PARAM(const_void) uaddr,
+                       unsigned int ulen)
 {
     struct param_hypfs *p;
     char *buf;
@@ -439,13 +442,15 @@ int hypfs_write_custom(struct hypfs_entry_leaf *leaf,
 }
 
 int hypfs_write_deny(struct hypfs_entry_leaf *leaf,
-                     XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned int ulen)
+                     XEN_GUEST_HANDLE_PARAM(const_void) uaddr,
+                     unsigned int ulen)
 {
     return -EACCES;
 }
 
 static int hypfs_write(struct hypfs_entry *entry,
-                       XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned long ulen)
+                       XEN_GUEST_HANDLE_PARAM(const_void) uaddr,
+                       unsigned long ulen)
 {
     struct hypfs_entry_leaf *l;
 
@@ -497,7 +502,7 @@ long do_hypfs_op(unsigned int cmd,
         break;
 
     case XEN_HYPFS_OP_write_contents:
-        ret = hypfs_write(entry, arg3, arg4);
+        ret = hypfs_write(entry, guest_handle_const_cast(arg3, void), arg4);
         break;
 
     default:

xen/include/xen/guest_access.h

@@ -26,6 +26,11 @@
     type *_x = (hnd).p;                         \
     (XEN_GUEST_HANDLE_PARAM(type)) { _x };      \
 })
+/* Same for casting to a const type. */
+#define guest_handle_const_cast(hnd, type) ({      \
+    const type *p_ = (hnd).p;                      \
+    (XEN_GUEST_HANDLE_PARAM(const_##type)) { p_ }; \
+})
 
 /* Cast a XEN_GUEST_HANDLE to XEN_GUEST_HANDLE_PARAM */
 #define guest_handle_to_param(hnd, type) ({                  \

xen/include/xen/hypfs.h

@@ -38,7 +38,7 @@ struct hypfs_funcs {
     int (*read)(const struct hypfs_entry *entry,
                 XEN_GUEST_HANDLE_PARAM(void) uaddr);
     int (*write)(struct hypfs_entry_leaf *leaf,
-                 XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned int ulen);
+                 XEN_GUEST_HANDLE_PARAM(const_void) uaddr, unsigned int ulen);
     unsigned int (*getsize)(const struct hypfs_entry *entry);
     struct hypfs_entry *(*findentry)(const struct hypfs_entry_dir *dir,
                                      const char *name, unsigned int name_len);
@@ -154,13 +154,17 @@ int hypfs_read_dir(const struct hypfs_entry *entry,
 int hypfs_read_leaf(const struct hypfs_entry *entry,
                     XEN_GUEST_HANDLE_PARAM(void) uaddr);
 int hypfs_write_deny(struct hypfs_entry_leaf *leaf,
-                     XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned int ulen);
+                     XEN_GUEST_HANDLE_PARAM(const_void) uaddr,
+                     unsigned int ulen);
 int hypfs_write_leaf(struct hypfs_entry_leaf *leaf,
-                     XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned int ulen);
+                     XEN_GUEST_HANDLE_PARAM(const_void) uaddr,
+                     unsigned int ulen);
 int hypfs_write_bool(struct hypfs_entry_leaf *leaf,
-                     XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned int ulen);
+                     XEN_GUEST_HANDLE_PARAM(const_void) uaddr,
+                     unsigned int ulen);
 int hypfs_write_custom(struct hypfs_entry_leaf *leaf,
-                       XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned int ulen);
+                       XEN_GUEST_HANDLE_PARAM(const_void) uaddr,
+                       unsigned int ulen);
 unsigned int hypfs_getsize(const struct hypfs_entry *entry);
 struct hypfs_entry *hypfs_leaf_findentry(const struct hypfs_entry_dir *dir,
                                          const char *name,