[libc] Rework the 'fgets' implementation on the GPU

libc/include/llvm-libc-types/rpc_opcodes_t.h

@@ -17,6 +17,7 @@ typedef enum {
   RPC_WRITE_TO_STREAM,
   RPC_WRITE_TO_STDOUT_NEWLINE,
   RPC_READ_FROM_STREAM,
+  RPC_READ_FGETS,
   RPC_OPEN_FILE,
   RPC_CLOSE_FILE,
   RPC_MALLOC,

libc/src/stdio/gpu/fgets.cpp

@@ -22,24 +22,20 @@ LLVM_LIBC_FUNCTION(char *, fgets,
   if (count < 1)
     return nullptr;
 
-  // This implementation is very slow as it makes multiple RPC calls.
-  unsigned char c = '\0';
-  int i = 0;
-  for (; i < count - 1 && c != '\n'; ++i) {
-    auto r = file::read(stream, &c, 1);
-    if (r != 1)
-      break;
-
-    str[i] = c;
-  }
-
-  bool has_error = LIBC_NAMESPACE::ferror(stream);
-  bool has_eof = LIBC_NAMESPACE::feof(stream);
-
-  if (has_error || (i == 0 && has_eof))
+  uint64_t recv_size;
+  void *buf = nullptr;
+  rpc::Client::Port port = rpc::client.open<RPC_READ_FGETS>();
+  port.send([=](rpc::Buffer *buffer) {
+    buffer->data[0] = count;
+    buffer->data[1] = file::from_stream(stream);
+  });
+  port.recv_n(&buf, &recv_size,
+              [&](uint64_t) { return reinterpret_cast<void *>(str); });
+  port.close();
+
+  if (recv_size == 0)
     return nullptr;
 
-  str[i] = '\0';
   return str;
 }
 

libc/utils/gpu/server/rpc_server.cpp

@@ -101,6 +101,22 @@ struct Server {
       });
       break;
     }
+    case RPC_READ_FGETS: {
+      uint64_t sizes[lane_size] = {0};
+      void *data[lane_size] = {nullptr};
+      port->recv([&](rpc::Buffer *buffer, uint32_t id) {
+        data[id] = new char[buffer->data[0]];
+        const char *str =
+            fgets(reinterpret_cast<char *>(data[id]), buffer->data[0],
+                  file::to_stream(buffer->data[1]));
+        sizes[id] = !str ? 0 : std::strlen(str) + 1;
+      });
+      port->send_n(data, sizes);
+      for (uint32_t id = 0; id < lane_size; ++id)
+        if (data[id])
+          delete[] reinterpret_cast<uint8_t *>(data[id]);
+      break;
+    }
     case RPC_OPEN_FILE: {
       uint64_t sizes[lane_size] = {0};
       void *paths[lane_size] = {nullptr};