[PATCH v2 4/5] xen/version: Fold build_id handling into xenver_varbuf_op()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

struct xen_build_id and struct xen_varbuf are identical from an ABI point of
view, so XENVER_build_id can reuse xenver_varbuf_op() rather than having it's
own almost identical copy of the logic.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Julien Grall <julien@xxxxxxx>

v2:
 * New
---
 xen/common/kernel.c          | 49 +++++++++++++-------------------------------
 xen/include/public/version.h |  5 ++++-
 2 files changed, 18 insertions(+), 36 deletions(-)

diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index cc5d8247b04d..7ab410ac7c28 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -476,9 +476,22 @@ static long xenver_varbuf_op(int cmd, 
XEN_GUEST_HANDLE_PARAM(void) arg)
     struct xen_varbuf user_str;
     const char *str = NULL;
     size_t sz;
+    int rc;
 
     switch ( cmd )
     {
+    case XENVER_build_id:
+    {
+        unsigned int local_sz;
+
+        rc = xen_build_id((const void **)&str, &local_sz);
+        if ( rc )
+            return rc;
+
+        sz = local_sz;
+        goto have_len;
+    }
+
     case XENVER_extraversion2:
         str = xen_extra_version();
         break;
@@ -502,6 +515,7 @@ static long xenver_varbuf_op(int cmd, 
XEN_GUEST_HANDLE_PARAM(void) arg)
 
     sz = strlen(str);
 
+ have_len:
     if ( sz > KB(64) ) /* Arbitrary limit.  Avoid long-running operations. */
         return -E2BIG;
 
@@ -703,41 +717,6 @@ long do_xen_version(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
arg)
     }
 
     case XENVER_build_id:
-    {
-        xen_build_id_t build_id;
-        unsigned int sz;
-        int rc;
-        const void *p;
-
-        if ( deny )
-            return -EPERM;
-
-        /* Only return size. */
-        if ( !guest_handle_is_null(arg) )
-        {
-            if ( copy_from_guest(&build_id, arg, 1) )
-                return -EFAULT;
-
-            if ( build_id.len == 0 )
-                return -EINVAL;
-        }
-
-        rc = xen_build_id(&p, &sz);
-        if ( rc )
-            return rc;
-
-        if ( guest_handle_is_null(arg) )
-            return sz;
-
-        if ( sz > build_id.len )
-            return -ENOBUFS;
-
-        if ( copy_to_guest_offset(arg, offsetof(xen_build_id_t, buf), p, sz) )
-            return -EFAULT;
-
-        return sz;
-    }
-
     case XENVER_extraversion2:
     case XENVER_capabilities2:
     case XENVER_changeset2:
diff --git a/xen/include/public/version.h b/xen/include/public/version.h
index 9287b5d3ff50..ee32d4c6b30b 100644
--- a/xen/include/public/version.h
+++ b/xen/include/public/version.h
@@ -124,8 +124,10 @@ typedef char xen_commandline_t[1024];
 /*
  * Return value is the number of bytes written, or XEN_Exx on error.
  * Calling with empty parameter returns the size of build_id.
+ *
+ * Note: structure only kept for backwards compatibility.  Xen operates in
+ * terms of xen_varbuf_t.
  */
-#define XENVER_build_id 10
 struct xen_build_id {
         uint32_t        len; /* IN: size of buf[]. */
         unsigned char   buf[XEN_FLEX_ARRAY_DIM];
@@ -164,6 +166,7 @@ typedef struct xen_varbuf xen_varbuf_t;
  * effect.  e.g. Xen has no control over the formatting used for the command
  * line.
  */
+#define XENVER_build_id      10
 #define XENVER_extraversion2 11
 #define XENVER_capabilities2 12
 #define XENVER_changeset2    13
-- 
2.11.0