diff --git a/eeshow/file.c b/eeshow/file.c
index d2718c6..6910899 100644
--- a/eeshow/file.c
+++ b/eeshow/file.c
@@ -22,6 +22,24 @@
 #include "file.h"
 
 
+void *file_oid(const struct file *file)
+{
+	if (!file->vcs)
+		return NULL;
+	return vcs_git_get_oid(file->vcs);
+}
+
+
+bool file_oid_eq(const void *a, const void *b)
+{
+	/*
+	 * If both a and b are NULL, we don't have revision data and thus
+	 * can't tell if they're identical.
+	 */
+	return a && b && vcs_git_oid_eq(a, b);
+}
+
+
 bool file_cat(const struct file *file, void *user, const char *line)
 {
 	printf("%s\n", line);
diff --git a/eeshow/file.h b/eeshow/file.h
index 10d012d..4d5f886 100644
--- a/eeshow/file.h
+++ b/eeshow/file.h
@@ -26,6 +26,9 @@ struct file {
 };
 
 
+void *file_oid(const struct file *file);
+bool file_oid_eq(const void *a, const void *b);
+
 bool file_cat(const struct file *file, void *user, const char *line);
 
 char *file_graft_relative(const char *base, const char *name);
diff --git a/eeshow/git-file.c b/eeshow/git-file.c
index 26ff1c6..78d4a9b 100644
--- a/eeshow/git-file.c
+++ b/eeshow/git-file.c
@@ -34,12 +34,36 @@ struct vcs_git {
 
 	git_repository *repo;
 	git_tree *tree;
+	git_object *obj;
 
 	const void *data;
 	unsigned size;
 };
 
 
+/* ----- OID matching ------------------------------------------------------ */
+
+
+void *vcs_git_get_oid(const void *ctx)
+{
+	const struct vcs_git *vcs_git = ctx;
+	struct git_oid *new;
+
+	new = alloc_type(git_oid);
+	git_oid_cpy(new, git_object_id(vcs_git->obj));
+	return new;
+}
+
+
+bool vcs_git_oid_eq(const void *a, const void *b)
+{
+	return !git_oid_cmp(a, b);
+}
+
+
+/* ----- Open -------------------------------------------------------------- */
+
+
 static git_repository *select_repo(const char *path)
 {
 	git_repository *repo = NULL;
@@ -298,9 +322,10 @@ static git_tree_entry *find_file(git_repository *repo, git_tree *tree,
 }
 
 
-static const void *get_data(git_repository *repo, git_tree_entry *entry,
+static const void *get_data(struct vcs_git *vcs_git, git_tree_entry *entry,
     unsigned *size)
 {
+	git_repository *repo =vcs_git->repo;
 	git_object *obj;
 	git_blob *blob;
 
@@ -314,6 +339,7 @@ static const void *get_data(git_repository *repo, git_tree_entry *entry,
 		fprintf(stderr, "%s\n", e->message);
 		exit(1);
 	}
+	vcs_git->obj = obj;
 
 	if (verbose > 2) {
 		git_buf buf = { 0 };
@@ -358,7 +384,7 @@ static bool access_file_data(struct vcs_git *vcs_git, const char *name)
 	if (verbose)
 		fprintf(stderr, "reading %s\n", name);
 
-	vcs_git->data = get_data(vcs_git->repo, entry, &vcs_git->size);
+	vcs_git->data = get_data(vcs_git, entry, &vcs_git->size);
 	return 1;
 }
 
@@ -467,6 +493,9 @@ fail:
 }
 
 
+/* ----- Read -------------------------------------------------------------- */
+
+
 bool vcs_git_read(void *ctx, struct file *file,
     bool (*parse)(const struct file *file, void *user, const char *line),
     void *user)
@@ -489,6 +518,9 @@ bool vcs_git_read(void *ctx, struct file *file,
 }
 
 
+/* ----- Close ------------------------------------------------------------- */
+
+
 void vcs_git_close(void *ctx)
 {
 	struct vcs_git *vcs_git = ctx;
diff --git a/eeshow/git-file.h b/eeshow/git-file.h
index 7faba3a..973aedb 100644
--- a/eeshow/git-file.h
+++ b/eeshow/git-file.h
@@ -32,6 +32,9 @@ struct file;
 
 void vcs_git_init(void);
 
+void *vcs_git_get_oid(const void *ctx);	/* mallocs */
+bool vcs_git_oid_eq(const void *a, const void *b);
+
 struct vcs_git *vcs_git_open(const char *revision, const char *name,
     const struct vcs_git *related);
 bool vcs_git_read(void *ctx, struct file *file,