[k2] add fstat (#1515)

Author: denisichh

runtime-light/k2-platform/k2-api.h

@@ -426,6 +426,13 @@ inline auto canonicalize(std::string_view path) noexcept {
   return return_type{{unique_ptr_type{resolved_path, std::invoke(deleter_creator, resolved_path_len, resolved_path_align)}, resolved_path_len}};
 }
 
+inline std::expected<void, int32_t> fstat(k2::descriptor fd, struct stat* stat) noexcept {
+  if (auto error_code{k2_fstat(fd, stat)}; error_code != k2::errno_ok) [[unlikely]] {
+    return std::unexpected{error_code};
+  }
+  return {};
+}
+
 inline std::expected<void, int32_t> stat(std::string_view path, struct stat* stat) noexcept {
   if (auto error_code{k2_stat(path.data(), path.size(), stat)}; error_code != k2::errno_ok) [[unlikely]] {
     return std::unexpected{error_code};

runtime-light/k2-platform/k2-header.h

@@ -732,6 +732,11 @@ size_t k2_backtrace(void** buffer, size_t size);
  */
 int32_t k2_canonicalize(const char* path, size_t pathlen, char* const* resolved_path, size_t* resolved_pathlen, size_t* resolved_path_align);
 
+/**
+ * Semantically equivalent to libc's `fstat`.
+ */
+int32_t k2_fstat(uint64_t fd, struct stat* statbuf);
+
 /**
  * Semantically equivalent to libc's `stat`.
  *