cpio: Symbolic link support

Add symbolic link support to cpiod.so parser.  As OSv does not yet
support symlinks, the files are never created on the filesystem.

This is needed for streaming rpm2cpio to OSv guest.

Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

tools/cpiod/cpio.cc

@@ -96,6 +96,13 @@ bool cpio_in::parse_one(istream& is, cpio_in& out)
         out.add_file(name, file);
         break;
     }
+    case C_ISLNK: {
+        unique_ptr<char[]> targetbuf{new char[filesize]};
+        is.read(targetbuf.get(), filesize);
+        string target{targetbuf.get(), filesize};
+        out.add_symlink(name, target);
+	break;
+    }
     default:
         cout << name << ": unknown type " << type << "\n";
         is.ignore(filesize);

tools/cpiod/cpio.hh

@@ -18,6 +18,7 @@ class cpio_in {
 public:
     virtual ~cpio_in();
     virtual void add_file(std::string name, std::istream& is) = 0;
+    virtual void add_symlink(std::string oldpath, std::string newpath) = 0;
 public:
     static void parse(std::istream& is, cpio_in& out);
 private:

tools/cpiod/cpiod.cc

@@ -34,6 +34,9 @@ public:
         ofstream os(name);
         os << is.rdbuf();
     }
+    virtual void add_symlink(string oldpath, string newpath) override {
+        cout << "Skipping symlink " << oldpath << "...\n";
+    }
 
 private:
     std::string _prefix;