Merge pull request containers#4459 from giuseppe/fix-renameat-definition

rootless: use SYS_renameat2 instead of __NR_renameat2

pkg/rootless/rootless_linux.c

@@ -24,12 +24,16 @@
 
 int renameat2 (int olddirfd, const char *oldpath, int newdirfd, const char *newpath, unsigned int flags)
 {
-# ifdef __NR_renameat2
-  return (int) syscall (__NR_renameat2, olddirfd, oldpath, newdirfd, newpath, flags);
+# ifdef SYS_renameat2
+  return (int) syscall (SYS_renameat2, olddirfd, oldpath, newdirfd, newpath, flags);
 # else
-  /* no way to implement it atomically.  */
-  errno = ENOSYS;
-  return -1;
+  /* This might be an issue if another process is trying to read the file while it is empty.  */
+  int fd = open (newpath, O_EXCL|O_CREAT, 0700);
+  if (fd < 0)
+    return fd;
+  close (fd);
+  /* We are sure we created the file, let's overwrite it.  */
+  return rename (oldpath, newpath);
 # endif
 }
 #endif