Changeset 60346 in vbox for trunk

Timestamp:

Apr 6, 2016 9:34:14 AM (9 years ago)

Author:

vboxsync

Message:

Runtime/sg.cpp: Allow RTSgBufInit to take NULL and 0 for paSegs and cSegs respectively to indicate an empty buffer

Location:

trunk

Files:

• include/iprt/sg.h (modified) (1 diff)
• src/VBox/Runtime/common/misc/sg.cpp (modified) (3 diffs)

trunk/include/iprt/sg.h

@@ -80 +80 @@
  * @param   paSegs    Pointer to the start of the segment array.
  * @param   cSegs     Number of segments in the array.
+ *
+ * @note paSegs and cSegs can be NULL and 0 respectively to indicate
+ *       an empty S/G buffer. All operations on the S/G buffer will
+ *       not do anything in this case.
  */
 RTDECL(void) RTSgBufInit(PRTSGBUF pSgBuf, PCRTSGSEG paSegs, size_t cSegs);

trunk/src/VBox/Runtime/common/misc/sg.cpp

@@ -84 +84 @@
 {
     AssertPtr(pSgBuf);
-    AssertPtr(paSegs);
-    Assert(cSegs > 0);
+    Assert(   (cSegs > 0 && VALID_PTR(paSegs))
+           || (!cSegs && !paSegs));
     Assert(cSegs < (~(unsigned)0 >> 1));
 
@@ -91 +91 @@
     pSgBuf->cSegs     = (unsigned)cSegs;
     pSgBuf->idxSeg    = 0;
-    pSgBuf->pvSegCur  = paSegs[0].pvSeg;
-    pSgBuf->cbSegLeft = paSegs[0].cbSeg;
+    if (cSegs && paSegs)
+    {
+        pSgBuf->pvSegCur  = paSegs[0].pvSeg;
+        pSgBuf->cbSegLeft = paSegs[0].cbSeg;
+    }
+    else
+    {
+        pSgBuf->pvSegCur  = NULL;
+        pSgBuf->cbSegLeft = 0;
+    }
 }
 
@@ -100 +108 @@
     AssertPtrReturnVoid(pSgBuf);
 
-    pSgBuf->idxSeg    = 0;
-    pSgBuf->pvSegCur  = pSgBuf->paSegs[0].pvSeg;
-    pSgBuf->cbSegLeft = pSgBuf->paSegs[0].cbSeg;
+    pSgBuf->idxSeg = 0;
+    if (pSgBuf->cSegs)
+    {
+        pSgBuf->pvSegCur  = pSgBuf->paSegs[0].pvSeg;
+        pSgBuf->cbSegLeft = pSgBuf->paSegs[0].cbSeg;
+    }
+    else
+    {
+        pSgBuf->pvSegCur  = NULL;
+        pSgBuf->cbSegLeft = 0;
+    }
 }