v3, 3 partsSupport virtual repositories in smart http-backend, specified by environment

builtin/receive-pack.c, upload-pack.c

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index e1ba4dc..76dacd0 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -34,6 +34,8 @@ static int prefer_ofs_delta = 1;
 static int auto_update_server_info;
 static int auto_gc = 1;
 static const char *head_name;
+static const char *head_path = "HEAD";
+static const char *ref_prefix = "refs/";
 static int sent_capabilities;
 
 static enum deny_action parse_deny_action(const char *var, const char *value)
@@ -108,11 +110,12 @@ static int receive_pack_config(const char *var, const char *value, void *cb)
 
 static int show_ref(const char *path, const unsigned char *sha1, int flag, void *cb_data)
 {
+	const char *refnameprefix = cb_data;
 	if (sent_capabilities)
-		packet_write(1, "%s %s\n", sha1_to_hex(sha1), path);
+		packet_write(1, "%s %s%s\n", sha1_to_hex(sha1), refnameprefix, path);
 	else
-		packet_write(1, "%s %s%c%s%s\n",
-			     sha1_to_hex(sha1), path, 0,
+		packet_write(1, "%s %s%s%c%s%s\n",
+			     sha1_to_hex(sha1), refnameprefix, path, 0,
 			     " report-status delete-refs side-band-64k",
 			     prefer_ofs_delta ? " ofs-delta" : "");
 	sent_capabilities = 1;
@@ -121,9 +124,9 @@ static int show_ref(const char *path, const unsigned char *sha1, int flag, void
 
 static void write_head_info(void)
 {
-	for_each_ref(show_ref, NULL);
+	for_each_ref_in(ref_prefix, show_ref, "refs/");
 	if (!sent_capabilities)
-		show_ref("capabilities^{}", null_sha1, 0, NULL);
+		show_ref("capabilities^{}", null_sha1, 0, "");
 
 }
 
@@ -332,6 +335,8 @@ static void refuse_unconfigured_deny_delete_current(void)
 static const char *update(struct command *cmd)
 {
 	const char *name = cmd->ref_name;
+	struct strbuf prefixed_name_buf = STRBUF_INIT;
+	const char *prefixed_name;
 	unsigned char *old_sha1 = cmd->old_sha1;
 	unsigned char *new_sha1 = cmd->new_sha1;
 	struct ref_lock *lock;
@@ -342,7 +347,10 @@ static const char *update(struct command *cmd)
 		return "funny refname";
 	}
 
-	if (is_ref_checked_out(name)) {
+	strbuf_addf(&prefixed_name_buf, "%s%s", ref_prefix, name + 5);
+	prefixed_name = strbuf_detach(&prefixed_name_buf, NULL);
+
+	if (is_ref_checked_out(prefixed_name)) {
 		switch (deny_current_branch) {
 		case DENY_IGNORE:
 			break;
@@ -370,7 +378,7 @@ static const char *update(struct command *cmd)
 			return "deletion prohibited";
 		}
 
-		if (!strcmp(name, head_name)) {
+		if (!strcmp(prefixed_name, head_name)) {
 			switch (deny_delete_current) {
 			case DENY_IGNORE:
 				break;
@@ -426,14 +434,14 @@ static const char *update(struct command *cmd)
 			rp_warning("Allowing deletion of corrupt ref.");
 			old_sha1 = NULL;
 		}
-		if (delete_ref(name, old_sha1, 0)) {
+		if (delete_ref(prefixed_name, old_sha1, 0)) {
 			rp_error("failed to delete %s", name);
 			return "failed to delete";
 		}
 		return NULL; /* good */
 	}
 	else {
-		lock = lock_any_ref_for_update(name, old_sha1, 0);
+		lock = lock_any_ref_for_update(prefixed_name, old_sha1, 0);
 		if (!lock) {
 			rp_error("failed to lock %s", name);
 			return "failed to lock";
@@ -760,6 +768,16 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 				advertise_refs = 1;
 				continue;
 			}
+			if (!prefixcmp(arg, "--head=")) {
+				head_path = arg+7;
+				continue;
+			}
+			if (!prefixcmp(arg, "--ref-prefix=")) {
+				struct strbuf prefixbuf = STRBUF_INIT;
+				strbuf_addf(&prefixbuf, "refs/%s", arg+13);
+				ref_prefix = strbuf_detach(&prefixbuf, NULL);
+				continue;
+			}
 			if (!strcmp(arg, "--stateless-rpc")) {
 				stateless_rpc = 1;
 				continue;
diff --git a/upload-pack.c b/upload-pack.c
index ce5cbbe..a1e495f 100644
--- a/upload-pack.c
+++ b/upload-pack.c
@@ -34,6 +34,8 @@ static int shallow_nr;
 static struct object_array have_obj;
 static struct object_array want_obj;
 static struct object_array extra_edge_obj;
+static const char *head_path = "HEAD";
+static const char *ref_prefix = "";
 static unsigned int timeout;
 /* 0 for no sideband,
  * otherwise maximum packet size (up to 65520 bytes).
@@ -640,17 +642,18 @@ static int send_ref(const char *refname, const unsigned char *sha1, int flag, vo
 	static const char *capabilities = "multi_ack thin-pack side-band"
 		" side-band-64k ofs-delta shallow no-progress"
 		" include-tag multi_ack_detailed";
+	const char *refnameprefix = cb_data;
 	struct object *o = parse_object(sha1);
 
 	if (!o)
 		die("git upload-pack: cannot find object %s:", sha1_to_hex(sha1));
 
 	if (capabilities)
-		packet_write(1, "%s %s%c%s%s\n", sha1_to_hex(sha1), refname,
+		packet_write(1, "%s %s%s%c%s%s\n", sha1_to_hex(sha1), refnameprefix, refname,
 			     0, capabilities,
 			     stateless_rpc ? " no-done" : "");
 	else
-		packet_write(1, "%s %s\n", sha1_to_hex(sha1), refname);
+		packet_write(1, "%s %s%s\n", sha1_to_hex(sha1), refnameprefix, refname);
 	capabilities = NULL;
 	if (!(o->flags & OUR_REF)) {
 		o->flags |= OUR_REF;
@@ -659,7 +662,7 @@ static int send_ref(const char *refname, const unsigned char *sha1, int flag, vo
 	if (o->type == OBJ_TAG) {
 		o = deref_tag(o, refname, 0);
 		if (o)
-			packet_write(1, "%s %s^{}\n", sha1_to_hex(o->sha1), refname);
+			packet_write(1, "%s %s%s^{}\n", sha1_to_hex(o->sha1), refnameprefix, refname);
 	}
 	return 0;
 }
@@ -678,15 +681,24 @@ static int mark_our_ref(const char *refname, const unsigned char *sha1, int flag
 
 static void upload_pack(void)
 {
+	struct strbuf prefix = STRBUF_INIT;
+	unsigned char sha1[20];
+	int flag;
+
+	strbuf_addf(&prefix, "refs/%s", ref_prefix);
 	if (advertise_refs || !stateless_rpc) {
 		reset_timeout();
-		head_ref(send_ref, NULL);
-		for_each_ref(send_ref, NULL);
+		if (resolve_ref(head_path, sha1, 1, &flag))
+			send_ref("HEAD", sha1, flag, "");
+		for_each_ref_in(prefix.buf, send_ref, "refs/");
 		packet_flush(1);
 	} else {
-		head_ref(mark_our_ref, NULL);
-		for_each_ref(mark_our_ref, NULL);
+		if (resolve_ref(head_path, sha1, 1, &flag))
+			mark_our_ref("HEAD", sha1, flag, NULL);
+		for_each_ref_in(prefix.buf, mark_our_ref, NULL);
 	}
+	strbuf_release(&prefix);
+
 	if (advertise_refs)
 		return;
 
@@ -716,6 +728,14 @@ int main(int argc, char **argv)
 			advertise_refs = 1;
 			continue;
 		}
+		if (!prefixcmp(arg, "--head=")) {
+			head_path = arg+7;
+			continue;
+		}
+		if (!prefixcmp(arg, "--ref-prefix=")) {
+			ref_prefix = arg+13;
+			continue;
+		}
 		if (!strcmp(arg, "--stateless-rpc")) {
 			stateless_rpc = 1;
 			continue;

Documentation/git-http-backend.txt, http-backend.c

diff --git a/Documentation/git-http-backend.txt b/Documentation/git-http-backend.txt
index 277d9e1..4e0b243 100644
--- a/Documentation/git-http-backend.txt
+++ b/Documentation/git-http-backend.txt
@@ -119,6 +119,14 @@ ScriptAliasMatch \
 
 ScriptAlias /git/ /var/www/cgi-bin/gitweb.cgi/
 ----------------------------------------------------------------
++
+To serve multiple virtual repositories from a single storage
+repository:
++
+----------------------------------------------------------------
+SetEnvIf Request_URI "^/git/([^/]*)" GIT_REF_PREFIX=$1/ GIT_HEAD=$1-HEAD
+ScriptAliasMatch ^/git/[^/]*(.*) /usr/libexec/git-core/git-http-backend/storage.git$1
+----------------------------------------------------------------
 
 Accelerated static Apache 2.x::
 	Similar to the above, but Apache can be used to return static
@@ -167,6 +175,12 @@ The GIT_HTTP_EXPORT_ALL environmental variable may be passed to
 'git-http-backend' to bypass the check for the "git-daemon-export-ok"
 file in each repository before allowing export of that repository.
 
+The GIT_REF_PREFIX and GIT_HEAD environment variables allow
+http-backend to support multiple virtual repositories within a single
+storage repository.  If set, 'git http-backend' will operate on
+'refs/${GIT_REF_PREFIX}' rather than 'refs/', and '$GIT_HEAD' rather
+than HEAD.
+
 The backend process sets GIT_COMMITTER_NAME to '$REMOTE_USER' and
 GIT_COMMITTER_EMAIL to '$\{REMOTE_USER}@http.$\{REMOTE_ADDR\}',
 ensuring that any reflogs created by 'git-receive-pack' contain some
diff --git a/http-backend.c b/http-backend.c
index 8501504..3d9e3b1 100644
--- a/http-backend.c
+++ b/http-backend.c
@@ -315,16 +315,23 @@ done:
 	close(out);
 }
 
-static void run_service(const char **argv)
+#define RUN_SERVICE_LAST_EXTRA_ARG 2
+#define RUN_SERVICE_EXTRA_ARGS NULL, NULL, NULL
+
+static void run_service(const char *argv0, const char **argv)
 {
 	const char *encoding = getenv("HTTP_CONTENT_ENCODING");
 	const char *user = getenv("REMOTE_USER");
 	const char *host = getenv("REMOTE_ADDR");
+	char *ref_prefix = getenv("GIT_REF_PREFIX");
+	char *head = getenv("GIT_HEAD");
 	char *env[3];
 	struct strbuf buf = STRBUF_INIT;
 	int gzipped_request = 0;
 	struct child_process cld;
 
+	argv += RUN_SERVICE_LAST_EXTRA_ARG;
+
 	if (encoding && !strcmp(encoding, "gzip"))
 		gzipped_request = 1;
 	else if (encoding && !strcmp(encoding, "x-gzip"))
@@ -343,6 +350,24 @@ static void run_service(const char **argv)
 	env[1] = strbuf_detach(&buf, NULL);
 	env[2] = NULL;
 
+	if (ref_prefix && !*ref_prefix)
+		ref_prefix = NULL;
+	if (ref_prefix) {
+		strbuf_addf(&buf, "--ref-prefix=%s", ref_prefix);
+		ref_prefix = strbuf_detach(&buf, NULL);
+		*argv-- = ref_prefix;
+	}
+
+	if (head && !*head)
+		head = NULL;
+	if (head) {
+		strbuf_addf(&buf, "--head=%s", head);
+		head = strbuf_detach(&buf, NULL);
+		*argv-- = head;
+	}
+
+	*argv = argv0;
+
 	memset(&cld, 0, sizeof(cld));
 	cld.argv = argv;
 	cld.env = (const char *const *)env;
@@ -362,6 +387,8 @@ static void run_service(const char **argv)
 		exit(1);
 	free(env[0]);
 	free(env[1]);
+	free(ref_prefix);
+	free(head);
 	strbuf_release(&buf);
 }
 
@@ -391,7 +418,7 @@ static void get_info_refs(char *arg)
 	hdr_nocache();
 
 	if (service_name) {
-		const char *argv[] = {NULL /* service name */,
+		const char *argv[] = {RUN_SERVICE_EXTRA_ARGS,
 			"--stateless-rpc", "--advertise-refs",
 			".", NULL};
 		struct rpc_service *svc = select_service(service_name);
@@ -404,8 +431,7 @@ static void get_info_refs(char *arg)
 		packet_write(1, "# service=git-%s\n", svc->name);
 		packet_flush(1);
 
-		argv[0] = svc->name;
-		run_service(argv);
+		run_service(svc->name, argv);
 
 	} else {
 		select_getanyfile();
@@ -462,7 +488,7 @@ static void check_content_type(const char *accepted_type)
 
 static void service_rpc(char *service_name)
 {
-	const char *argv[] = {NULL, "--stateless-rpc", ".", NULL};
+	const char *argv[] = {RUN_SERVICE_EXTRA_ARGS, "--stateless-rpc", ".", NULL};
 	struct rpc_service *svc = select_service(service_name);
 	struct strbuf buf = STRBUF_INIT;
 
@@ -478,8 +504,7 @@ static void service_rpc(char *service_name)
 
 	end_headers();
 
-	argv[0] = svc->name;
-	run_service(argv);
+	run_service(svc->name, argv);
 	strbuf_release(&buf);
 }
 

Documentation/Makefile, Documentation/git-http-backend.txt, Documentation/gitvirtual.txt, contrib/completion/git-completion.bash

diff --git a/Documentation/Makefile b/Documentation/Makefile
index 36989b7..4b4bd2f 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -6,7 +6,7 @@ MAN5_TXT=gitattributes.txt gitignore.txt gitmodules.txt githooks.txt \
 	gitrepository-layout.txt
 MAN7_TXT=gitcli.txt gittutorial.txt gittutorial-2.txt \
 	gitcvs-migration.txt gitcore-tutorial.txt gitglossary.txt \
-	gitdiffcore.txt gitrevisions.txt gitworkflows.txt
+	gitdiffcore.txt gitrevisions.txt gitvirtual.txt gitworkflows.txt
 
 MAN_TXT = $(MAN1_TXT) $(MAN5_TXT) $(MAN7_TXT)
 MAN_XML=$(patsubst %.txt,%.xml,$(MAN_TXT))
diff --git a/Documentation/git-http-backend.txt b/Documentation/git-http-backend.txt
index 4e0b243..4a7c42b 100644
--- a/Documentation/git-http-backend.txt
+++ b/Documentation/git-http-backend.txt
@@ -120,8 +120,8 @@ ScriptAliasMatch \
 ScriptAlias /git/ /var/www/cgi-bin/gitweb.cgi/
 ----------------------------------------------------------------
 +
-To serve multiple virtual repositories from a single storage
-repository:
+To serve multiple virtual repositories (linkgit:gitvirtual[7]) from a
+single storage repository:
 +
 ----------------------------------------------------------------
 SetEnvIf Request_URI "^/git/([^/]*)" GIT_REF_PREFIX=$1/ GIT_HEAD=$1-HEAD
diff --git a/Documentation/gitvirtual.txt b/Documentation/gitvirtual.txt
new file mode 100644
index 0000000..ed5a4c5
--- /dev/null
+++ b/Documentation/gitvirtual.txt
@@ -0,0 +1,76 @@
+gitvirtual(7)
+=============
+
+NAME
+----
+gitvirtual - Git virtual repositories
+
+DESCRIPTION
+-----------
+
+Given many repositories with copies of the same objects (such as
+branches of the same source), sharing a common object store will avoid
+duplication.  Alternates provide a single baseline, but don't handle
+ongoing activity in the various repositories.  Furthermore, operations
+such as linkgit:git-gc[1] need to know about all of the refs.
+
+Git supports storing multiple virtual repositories within the object
+store and references of a single underlying repository.  The underlying
+repository stores the objects for all of the virtual repositories, and
+includes all the refs and heads of the virtual repositories using
+prefixed names.
+
+linkgit:git-upload-pack[1] and linkgit:git-receive-pack[1] rewrite the
+names of refs and heads as specified by the --ref-prefix and --head
+options.  For instance, --ref-prefix=`virtual/reponame/` will use
++pass:[refs/virtual/reponame/heads/*]+ and
++pass:[refs/virtual/reponame/tags/*]+.  git-upload-pack and
+git-receive-pack will ignore any references that do not match the
+specified prefix.
+
+These options implement the underlying mechanism for virtual
+repositories.  The smart HTTP server, linkgit:git-http-backend[1], can
+accept a ref prefix and HEAD path via environment variables, and pass
+them to the backend programs.  For a simple local test, you can use
+git-remote-ext:
+
+----------
+git clone ext::'git %s --ref-prefix=virtual/prefix/ --head=prefix-HEAD /tmp/prefixed.git'
+----------
+
+CONVENTIONS
+-----------
+
+The --ref-prefix and --head options provide quite a bit of flexibility
+in organizing the refs of virtual repositories within those of the
+underlying repository.  In the absence of a strong reason to do
+otherwise, consider following these conventions:
+
+--ref-prefix=`virtual/reponame/`::
+	This puts refs under `refs/virtual/reponame/`, which avoids a
+	namespace conflict between `reponame` and built-in ref
+	directories such as `heads` and `tags`.
+
+--head=`virtual-HEAD/reponame`::
+	This puts HEADs under `virtual-HEAD/` to avoid namespace
+	conflicts with top-level filenames in a git repository.
+
+SECURITY
+--------
+
+Anyone with access to any virtual repository can potentially access
+objects from any other virtual repository stored in the same underlying
+repository.  You can't directly say "give me object ABCD" if you don't
+have a ref to it, but you can do some other sneaky things like:
+
+. Claiming to push ABCD, at which point the server will optimize out the
+  need for you to actually send it. Now you have a ref to ABCD and can
+  fetch it (claiming not to have it, of course).
+
+. Requesting other refs, claiming that you have ABCD, at which point the
+  server may generate deltas against ABCD.
+
+None of this causes a problem if you only host public repositories, or
+if everyone who may read one virtual repo may also read everything in
+every other virtual repo (for instance, if everyone in an organization
+has read permission to every repository).
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index bb8d7d0..a58d27e 100755
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -1469,7 +1469,7 @@ _git_help ()
 		attributes cli core-tutorial cvs-migration
 		diffcore gitk glossary hooks ignore modules
 		repository-layout tutorial tutorial-2
-		workflows
+		virtual workflows
 		"
 }