Add the kernel tree's git revision to the hash

To better support kernel developers who work out of a single source
tree, this adds the git HEAD revision to our caching hash.

3 files changed, 32 insertions, 0 deletions

diff --git a/hash.cxx b/hash.cxx
index c9121641..649e7ec0 100644
--- a/hash.cxx
+++ b/hash.cxx
@@ -95,6 +95,10 @@ get_base_hash (systemtap_session& s, hash& h)
   h.add_file(s.kernel_build_tree + "/include/linux/version.h");
   h.add_file(s.kernel_build_tree + "/include/linux/utsrelease.h");
 
+  // If the kernel is a git working directory, then add the git HEAD
+  // revision to our hash as well.
+  h.add(git_revision(s.kernel_build_tree));
+
   // Hash runtime path (that gets added in as "-R path").
   h.add(s.runtime_path);
 
diff --git a/util.cxx b/util.cxx
index 7d191cd2..68cc27f7 100644
--- a/util.cxx
+++ b/util.cxx
@@ -248,4 +248,31 @@ const string cmdstr_quoted(const string& cmd)
 	return quoted_cmd;
 }
 
+
+string
+git_revision(const string& path)
+{
+  string revision = "(not-a-git-repository)";
+  string git_dir = path + "/.git/";
+
+  struct stat st;
+  if (stat(git_dir.c_str(), &st) == 0)
+    {
+      string command = "git --git-dir=\"" + git_dir
+        + "\" rev-parse HEAD 2>/dev/null";
+
+      char buf[50];
+      FILE *fp = popen(command.c_str(), "r");
+      if (fp != NULL)
+        {
+          char *bufp = fgets(buf, sizeof(buf), fp);
+          int rc = pclose(fp);
+          if (bufp != NULL && rc == 0)
+            revision = buf;
+        }
+    }
+
+  return revision;
+}
+
 /* vim: set sw=2 ts=8 cino=>4,n-2,{2,^-2,t0,(0,u0,w1,M1 : */
diff --git a/util.h b/util.h
index 2884e021..d385be02 100644
--- a/util.h
+++ b/util.h
@@ -12,6 +12,7 @@ void tokenize(const std::string& str, std::vector<std::string>& tokens,
 	      const std::string& delimiters);
 std::string find_executable(const std::string& name);
 const std::string cmdstr_quoted(const std::string& cmd);
+std::string git_revision(const std::string& path);
 
 
 // stringification generics