From 56ba8237e0a299187adda20bd7b0ddd1017450d4 Mon Sep 17 00:00:00 2001
From: Ben Peart <Ben.Peart@microsoft.com>
Date: Tue, 10 Jan 2017 18:47:14 +0000
Subject: [PATCH] gvfs: allow "virtualizing" objects

The idea is to allow blob objects to be missing from the local repository,
and to load them lazily on demand.

After discussing this idea on the mailing list, we will rename the feature
to "lazy clone" and work more on this.

Signed-off-by: Ben Peart <Ben.Peart@microsoft.com>
---
 cache.h       |  2 ++
 config.c      |  5 +++++
 connected.c   |  2 ++
 environment.c |  1 +
 object-file.c | 22 ++++++++++++++++++++++
 5 files changed, 32 insertions(+)

diff --git a/cache.h b/cache.h
index 26f2e04c61..ba8276fd25 100644
--- a/cache.h
+++ b/cache.h
@@ -1088,6 +1088,8 @@ int use_optional_locks(void);
 extern char comment_line_char;
 extern int auto_comment_line_char;
 
+extern int core_virtualize_objects;
+
 enum log_refs_config {
 	LOG_REFS_UNSET = -1,
 	LOG_REFS_NONE = 0,
diff --git a/config.c b/config.c
index 623e73d053..f0c2b78446 100644
--- a/config.c
+++ b/config.c
@@ -1753,6 +1753,11 @@ int git_default_core_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.virtualizeobjects")) {
+		core_virtualize_objects = git_config_bool(var, value);
+		return 0;
+	}
+
 	/* Add other config variables here and to Documentation/config.txt. */
 	return platform_core_config(var, value, cb);
 }
diff --git a/connected.c b/connected.c
index e9ae073015..9cde030ece 100644
--- a/connected.c
+++ b/connected.c
@@ -48,6 +48,8 @@ int check_connected(oid_iterate_fn fn, void *cb_data,
 	 */
 	if (gvfs_config_is_set(GVFS_FETCH_SKIP_REACHABILITY_AND_UPLOADPACK))
 		return 0;
+	if (core_virtualize_objects)
+		return 0;
 
 	if (!opt)
 		opt = &defaults;
diff --git a/environment.c b/environment.c
index 2538af1da7..49f6da4b08 100644
--- a/environment.c
+++ b/environment.c
@@ -77,6 +77,7 @@ int core_gvfs;
 int merge_log_config = -1;
 int precomposed_unicode = -1; /* see probe_utf8_pathname_composition() */
 unsigned long pack_size_limit_cfg;
+int core_virtualize_objects;
 enum log_refs_config log_all_ref_updates = LOG_REFS_UNSET;
 
 #ifndef PROTECT_HFS_DEFAULT
diff --git a/object-file.c b/object-file.c
index f6257741b9..fab802f8e9 100644
--- a/object-file.c
+++ b/object-file.c
@@ -33,6 +33,7 @@
 #include "object-store.h"
 #include "promisor-remote.h"
 #include "submodule.h"
+#include "hook.h"
 
 /* The maximum size for an object header. */
 #define MAX_HEADER_LEN 32
@@ -1525,6 +1526,20 @@ void disable_obj_read_lock(void)
 	pthread_mutex_destroy(&obj_read_mutex);
 }
 
+static int run_read_object_hook(const struct object_id *oid)
+{
+	struct run_hooks_opt opt = RUN_HOOKS_OPT_INIT;
+	int ret;
+	uint64_t start;
+
+	start = getnanotime();
+	strvec_push(&opt.args, oid_to_hex(oid));
+	ret = run_hooks_opt("read-object", &opt);
+	trace_performance_since(start, "run_read_object_hook");
+
+	return ret;
+}
+
 int fetch_if_missing = 1;
 
 static int do_oid_object_info_extended(struct repository *r,
@@ -1537,6 +1552,7 @@ static int do_oid_object_info_extended(struct repository *r,
 	int rtype;
 	const struct object_id *real = oid;
 	int already_retried = 0;
+	int tried_hook = 0;
 
 
 	if (flags & OBJECT_INFO_LOOKUP_REPLACE)
@@ -1548,6 +1564,7 @@ static int do_oid_object_info_extended(struct repository *r,
 	if (!oi)
 		oi = &blank_oi;
 
+retry:
 	co = find_cached_object(real);
 	if (co) {
 		if (oi->typep)
@@ -1582,6 +1599,11 @@ static int do_oid_object_info_extended(struct repository *r,
 			reprepare_packed_git(r);
 			if (find_pack_entry(r, real, &e))
 				break;
+			if (core_virtualize_objects && !tried_hook) {
+				tried_hook = 1;
+				if (!run_read_object_hook(oid))
+					goto retry;
+			}
 		}
 
 		/*