"format-patch --root rev" is the way to show everything.

We used to trigger the special case "things not in origin"
semantics only when one and only one positive ref is given, and
no number (e.g. "git format-patch -4 origin") was specified, and
used the general revision range semantics for everything else.

This narrows the special case a bit more, by making:

	git format-patch --root this_version

to show everything that leads to the named commit.

More importantly, document the two different semantics better.
The generic revision range semantics came later and bolted on
without being clearly documented.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-format-patch.txt

@@ -16,21 +16,32 @@ SYNOPSIS
                    [--in-reply-to=Message-Id] [--suffix=.<sfx>]
                    [--ignore-if-in-upstream]
                    [--subject-prefix=Subject-Prefix]
-                   <since>[..<until>]
+		   [ <since> | <revision range> ]
 
 DESCRIPTION
 -----------
 
-Prepare each commit between <since> and <until> with its patch in
+Prepare each commit with its patch in
 one file per commit, formatted to resemble UNIX mailbox format.
-If ..<until> is not specified, the head of the current working
-tree is implied.  For a more complete list of ways to spell
-<since> and <until>, see "SPECIFYING REVISIONS" section in
-gitlink:git-rev-parse[1].
-
 The output of this command is convenient for e-mail submission or
 for use with gitlink:git-am[1].
 
+There are two ways to specify which commits to operate on.
+
+1. A single commit, <since>, specifies that the commits leading
+   to the tip of the current branch that are not in the history
+   that leads to the <since> to be output.
+
+2. Generic <revision range> expression (see "SPECIFYING
+   REVISIONS" section in gitlink:git-rev-parse[1]) means the
+   commits in the specified range.  A single commit, when
+   interpreted as a <revision range> expression, means
+   "everything that leads to that commit", but that is taken as
+   the special case above.  If you want to format everything
+   since project inception to one commit, say "git format-patch
+   \--root <that-commit>", as showing the root commit as patch
+   requires \--root option anyway.
+
 By default, each output file is numbered sequentially from 1, and uses the
 first line of the commit message (massaged for pathname safety) as
 the filename. With the --numbered-files option, the output file names
@@ -153,6 +164,10 @@ git-format-patch origin::
 	not in the origin branch.  For each commit a separate file
 	is created in the current directory.
 
+git-format-patch \--root origin::
+	Extract all commits which that leads to 'origin' since the
+	inception of the project.
+
 git-format-patch -M -B origin::
 	The same as the previous one.  Additionally, it detects
 	and handles renames and complete rewrites intelligently to

builtin-log.c

@@ -585,12 +585,19 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	}
 
 	if (rev.pending.nr == 1) {
-		if (rev.max_count < 0) {
+		if (rev.max_count < 0 && !rev.show_root_diff) {
+			/*
+			 * This is traditional behaviour of "git format-patch
+			 * origin" that prepares what the origin side still
+			 * does not have.
+			 */
 			rev.pending.objects[0].item->flags |= UNINTERESTING;
 			add_head(&rev);
 		}
-		/* Otherwise, it is "format-patch -22 HEAD", and
-		 * get_revision() would return only the specified count.
+		/*
+		 * Otherwise, it is "format-patch -22 HEAD", and/or
+		 * "format-patch --root HEAD".  The user wants
+		 * get_revision() to do the usual traversal.
 		 */
 	}