info: add MPIX_Info_set_hex

Add MPIX_Info_set_hex to allow user to provide info hints with binary
values. This routine provide a consistent way of encoding binary values
into string that implementation can decode.

src/binding/c/stream_api.txt

@@ -31,3 +31,9 @@ MPIX_Recv_enqueue:
 
 MPIX_Stream_synchronize:
     stream: STREAM, [stream object]
+
+MPIX_Info_set_hex:
+    info: INFO, direction=in, [info object]
+    key: STRING, constant=True, [key]
+    value: BUFFER, constant=True, [value]
+    value_size: INFO_VALUE_LENGTH, [size of value]

src/mpi/stream/stream_impl.c

@@ -28,39 +28,7 @@ int MPIR_Stream_free_impl(MPIR_Stream * stream_ptr)
  *
  * Returns MPICH error codes */
 
-static int hex_val(char c)
-{
-    if (c >= '0' && c <= '9') {
-        return c - '0';
-    } else if (c >= 'a' && c <= 'f') {
-        return c - 'a' + 10;
-    } else if (c >= 'A' && c <= 'F') {
-        return c - 'A' + 10;
-    } else {
-        return -1;
-    }
-}
-
-static int hex_decode(const char *str, void *buf, int len)
-{
-    int n = strlen(str);
-    if (n != len * 2) {
-        return 1;
-    }
-
-    unsigned char *s = buf;
-    for (int i = 0; i < len; i++) {
-        int a = hex_val(str[i * 2]);
-        int b = hex_val(str[i * 2 + 1]);
-        if (a < 0 || b < 0) {
-            return 1;
-        }
-        s[i] = (unsigned char) ((a << 4) + b);
-    }
-
-    return 0;
-}
-
+static int hex_decode(const char *str, void *buf, int len);
 int MPIR_Stream_create_impl(MPIR_Info * info_ptr, MPIR_Stream ** p_stream_ptr)
 {
     int mpi_errno = MPI_SUCCESS;
@@ -341,3 +309,66 @@ int MPIR_Stream_synchronize_impl(MPIR_Stream * stream_ptr)
 
     return mpi_errno;
 }
+
+static int hex_encode(char *str, const void *value, int len);
+int MPIR_Info_set_hex_impl(MPIR_Info * info_ptr, const char *key, const void *value, int value_size)
+{
+    int mpi_errno = MPI_SUCCESS;
+
+    char value_buf[1024];
+    MPIR_Assertp(value_size * 2 + 1 < 1024);
+
+    hex_encode(value_buf, value, value_size);
+
+    mpi_errno = MPIR_Info_set_impl(info_ptr, key, value_buf);
+
+    return mpi_errno;
+}
+
+/* ---- internal utility ---- */
+
+static int hex_val(char c)
+{
+    if (c >= '0' && c <= '9') {
+        return c - '0';
+    } else if (c >= 'a' && c <= 'f') {
+        return c - 'a' + 10;
+    } else if (c >= 'A' && c <= 'F') {
+        return c - 'A' + 10;
+    } else {
+        return -1;
+    }
+}
+
+static int hex_encode(char *str, const void *value, int len)
+{
+    /* assume the size of str is already validated */
+
+    const unsigned char *s = value;
+
+    for (int i = 0; i < len; i++) {
+        sprintf(str + i * 2, "%02x", s[i]);
+    }
+
+    return 0;
+}
+
+static int hex_decode(const char *str, void *buf, int len)
+{
+    int n = strlen(str);
+    if (n != len * 2) {
+        return 1;
+    }
+
+    unsigned char *s = buf;
+    for (int i = 0; i < len; i++) {
+        int a = hex_val(str[i * 2]);
+        int b = hex_val(str[i * 2 + 1]);
+        if (a < 0 || b < 0) {
+            return 1;
+        }
+        s[i] = (unsigned char) ((a << 4) + b);
+    }
+
+    return 0;
+}

test/mpi/impls/mpich/cuda/stream.cu

@@ -47,17 +47,6 @@ void saxpy(int n, float a, float *x, float *y)
   if (i < n) y[i] = a*x[i] + y[i];
 }
 
-static void hex_encode(char *buf, int len, cudaStream_t stream)
-{
-    int n = sizeof(cudaStream_t);
-    assert(len >= n * 2 + 1);
-
-    unsigned char *s = (unsigned char *) &stream;
-    for (int i = 0; i < n; i++) {
-        sprintf(buf + i * 2, "%02x", s[i]);
-    }
-}
-
 int main(void)
 {
     int errs = 0;
@@ -89,14 +78,10 @@ int main(void)
         init_y(y);
     }
 
-    /* hexadecimal encoding */
-    char str_stream[100];
-    hex_encode(str_stream, 100, stream);
-
     MPI_Info info;
     MPI_Info_create(&info);
     MPI_Info_set(info, "type", "cudaStream_t");
-    MPI_Info_set(info, "id", str_stream);
+    MPIX_Info_set_hex(info, "id", &stream, sizeof(stream));
 
     MPIX_Stream mpi_stream;
     MPIX_Stream_create(info, &mpi_stream);