Add support for FUSE passthrough

src/procfs.cpp

@@ -0,0 +1,77 @@
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
+#include "procfs.hpp"
+
+#include "errno.hpp"
+#include "fs_close.hpp"
+#include "fs_open.hpp"
+#include "fs_openat.hpp"
+#include "fs_read.hpp"
+
+#include "fmt/core.h"
+
+#include <array>
+#include <cassert>
+
+#include <pthread.h>
+
+static int g_PROCFS_DIR_FD = -1;
+namespace procfs { int PROC_SELF_FD_FD = -1; }
+static constexpr const char PROCFS_PATH[] = "/proc";
+static constexpr const char PROC_SELF_FD[] = "/proc/self/fd";
+
+// This is critical to the function of the app. abort if failed to
+// open.
+static
+void
+_open_proc_self_fd()
+{
+  procfs::PROC_SELF_FD_FD = fs::open(PROC_SELF_FD,O_PATH|O_DIRECTORY);
+  assert(procfs::PROC_SELF_FD_FD >= 0);
+}
+
+int
+procfs::init()
+{
+  if(g_PROCFS_DIR_FD != -1)
+    return 0;
+
+  g_PROCFS_DIR_FD = fs::open(PROCFS_PATH,O_PATH|O_DIRECTORY);
+  if(g_PROCFS_DIR_FD == -1)
+    return -errno;
+
+#if defined(__linux__)
+  ::_open_proc_self_fd();
+#endif
+
+  return 0;
+}
+
+std::string
+procfs::get_name(const int tid_)
+{
+  int fd;
+  int rv;
+  std::array<char,256> commpath;
+  fmt::format_to_n_result<char*> frv;
+
+  frv = fmt::format_to_n(commpath.data(),commpath.size()-1,"{}/comm",tid_);
+  frv.out[0] = '\0';
+
+  fd = fs::openat(g_PROCFS_DIR_FD,commpath.data(),O_RDONLY);
+  if(fd < 0)
+    return {};
+
+  rv = fs::read(fd,commpath.data(),commpath.size());
+  if(rv == -1)
+    return {};
+
+  // Overwrite the newline with NUL
+  commpath[rv-1] = '\0';
+
+  fs::close(fd);
+
+  return commpath.data();
+}