Introduce VIR_STREAM_RECV_STOP_AT_HOLE flag

Add a new flag to virStreamRecvFlags in order to handle being able to
stop reading from the stream so that the consumer can generate a "hole"
in stream target. Generation of a hole replaces the need to receive and
handle a sequence of zero bytes for sparse stream targets.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

include/libvirt/libvirt-stream.h

@@ -45,6 +45,10 @@ int virStreamRecv(virStreamPtr st,
                   char *data,
                   size_t nbytes);
 
+typedef enum {
+    VIR_STREAM_RECV_STOP_AT_HOLE = (1 << 0),
+} virStreamRecvFlagsValues;
+
 int virStreamRecvFlags(virStreamPtr st,
                        char *data,
                        size_t nbytes,

src/libvirt-stream.c

@@ -290,7 +290,7 @@ virStreamRecv(virStreamPtr stream,
  * @stream: pointer to the stream object
  * @data: buffer to read into from stream
  * @nbytes: size of @data buffer
- * @flags: extra flags; not used yet, so callers should always pass 0
+ * @flags: bitwise-OR of virStreamRecvFlagsValues
  *
  * Reads a series of bytes from the stream. This method may
  * block the calling application for an arbitrary amount
@@ -300,6 +300,33 @@ virStreamRecv(virStreamPtr stream,
  * @flags. Calling this function with no @flags set (equal to
  * zero) is equivalent to calling virStreamRecv(stream, data, nbytes).
  *
+ * If flag VIR_STREAM_RECV_STOP_AT_HOLE is set, this function
+ * will stop reading from stream if it has reached a hole. In
+ * that case, -3 is returned and virStreamRecvHole() should be
+ * called to get the hole size. An example using this flag might
+ * look like this:
+ *
+ *   while (1) {
+ *     char buf[4096];
+ *
+ *     int ret = virStreamRecvFlags(st, buf, len, VIR_STREAM_STOP_AT_HOLE);
+ *     if (ret < 0) {
+ *       if (ret == -3) {
+ *         long long len;
+ *         ret = virStreamRecvHole(st, &len, 0);
+ *         if (ret < 0) {
+ *           ...error..
+ *         } else {
+ *           ...seek len bytes in target...
+ *         }
+ *       } else {
+ *         return -1;
+ *       }
+ *     } else {
+ *         ...write buf to target...
+ *     }
+ *   }
+ *
  * Returns 0 when the end of the stream is reached, at
  * which time the caller should invoke virStreamFinish()
  * to get confirmation of stream completion.
@@ -310,6 +337,9 @@ virStreamRecv(virStreamPtr stream,
  *
  * Returns -2 if there is no data pending to be read & the
  * stream is marked as non-blocking.
+ *
+ * Returns -3 if there is a hole in stream and caller requested
+ * to stop at a hole.
  */
 int
 virStreamRecvFlags(virStreamPtr stream,
@@ -331,6 +361,8 @@ virStreamRecvFlags(virStreamPtr stream,
         ret = (stream->driver->streamRecvFlags)(stream, data, nbytes, flags);
         if (ret == -2)
             return -2;
+        if (ret == -3)
+            return -3;
         if (ret < 0)
             goto error;
         return ret;