virtualization: add new builtin command to print hydration level

GVFS users can easily (and accidentally) over-hydrate their
enlistments. This causes some commands to be very slow.

Create a command to print the current hydration level.  This
should help our support team investigate the state of their
enlistment.

Signed-off-by: Jeff Hostetler <jeffhostetler@github.com>

.gitignore

@@ -182,6 +182,7 @@
 /git-verify-pack
 /git-verify-tag
 /git-version
+/git-virtualization
 /git-web--browse
 /git-whatchanged
 /git-worktree

Documentation/git-virtualization.txt

@@ -0,0 +1,24 @@
+git-virtualization(1)
+=====================
+
+NAME
+----
+
+git-virtualization - EXPERIMENTAL: Measure virtualization level of worktree
+
+
+SYNOPSIS
+--------
+[verse]
+(EXPERIMENTAL!) `git virtualization` <options>
+
+
+DESCRIPTION
+-----------
+
+Measure the virtualization level of the worktree.
+
+
+GIT
+---
+Part of the linkgit:git[1] suite

Makefile

@@ -1346,6 +1346,7 @@ BUILTIN_OBJS += builtin/var.o
 BUILTIN_OBJS += builtin/verify-commit.o
 BUILTIN_OBJS += builtin/verify-pack.o
 BUILTIN_OBJS += builtin/verify-tag.o
+BUILTIN_OBJS += builtin/virtualization.o
 BUILTIN_OBJS += builtin/worktree.o
 BUILTIN_OBJS += builtin/write-tree.o
 

builtin.h

@@ -245,6 +245,7 @@ int cmd_var(int argc, const char **argv, const char *prefix);
 int cmd_verify_commit(int argc, const char **argv, const char *prefix);
 int cmd_verify_tag(int argc, const char **argv, const char *prefix);
 int cmd_version(int argc, const char **argv, const char *prefix);
+int cmd_virtualization(int argc, const char **argv, const char *prefix);
 int cmd_whatchanged(int argc, const char **argv, const char *prefix);
 int cmd_worktree(int argc, const char **argv, const char *prefix);
 int cmd_write_tree(int argc, const char **argv, const char *prefix);

builtin/virtualization.c

@@ -0,0 +1,102 @@
+#include "builtin.h"
+#include "config.h"
+#include "json-writer.h"
+#include "parse-options.h"
+#include "read-cache-ll.h"
+#include "repository.h"
+#include "trace2.h"
+
+static const char * const virt_usage[] = {
+	N_("(EXPERIMENTAL!) git virtualization"),
+	NULL,
+};
+
+static struct option virt_options[] = {
+	OPT_END(),
+};
+
+static int virt_load_config_cb(const char *var,
+			       const char *value,
+			       const struct config_context *ctx,
+			       void *pvoid)
+{
+	return git_default_config(var, value, ctx, pvoid);
+}
+
+static void virt_load_config(void)
+{
+	git_config(virt_load_config_cb, NULL);
+}
+
+static uint64_t count_skipped(struct repository *repo)
+{
+	uint64_t k;
+	uint64_t count = 0;
+
+	for (k = 0; k < repo->index->cache_nr; k++) {
+		const struct cache_entry *ce_k = repo->index->cache[k];
+
+		if (ce_skip_worktree(ce_k))
+			count++;
+	}
+
+	return count;
+}
+
+static void print_hydration(struct repository *repo)
+{
+	uint64_t c_skipped;
+	uint64_t c_total;
+	uint64_t c_hydrated;
+	double hydration;
+
+	c_skipped = count_skipped(the_repository);
+	c_total = (uint64_t)the_repository->index->cache_nr;
+	c_hydrated = c_total - c_skipped;
+
+	if (c_total > 0)
+		hydration = (double)(c_hydrated * 100) / (double)c_total;
+	else
+		hydration = 0.0;
+
+	printf("Skipped: %" PRIu64 "\n", c_skipped);
+	printf("Hydrated: %" PRIu64 "\n", c_hydrated);
+	printf("Total: %" PRIu64 "\n", c_total);
+
+	printf("Hydration: %.2f%%\n", hydration);
+
+	if (trace2_is_enabled()) {
+		struct json_writer jw = JSON_WRITER_INIT;
+
+		jw_object_begin(&jw, 0);
+		{
+			jw_object_intmax(&jw, "skipped", c_skipped);
+			jw_object_intmax(&jw, "hydrated", c_hydrated);
+			jw_object_intmax(&jw, "total", c_total);
+
+			jw_object_double(&jw, "hydration", 2, hydration);
+		}
+		jw_end(&jw);
+
+		trace2_data_json("virt", repo, "stats", &jw);
+
+		jw_release(&jw);
+	}
+}
+
+int cmd_virtualization(int argc, const char **argv, const char *prefix)
+{
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 1;
+
+	virt_load_config();
+
+	argc = parse_options(argc, argv, prefix, virt_options, virt_usage, 0);
+
+	if (repo_read_index(the_repository) < 0)
+		die("index file corrupt");
+
+	print_hydration(the_repository);
+
+	return 0;
+}

command-list.txt

@@ -201,6 +201,7 @@ git-verify-commit                       ancillaryinterrogators
 git-verify-pack                         plumbinginterrogators
 git-verify-tag                          ancillaryinterrogators
 git-version                             ancillaryinterrogators
+git-virtualization                      mainporcelain
 git-whatchanged                         ancillaryinterrogators          complete
 git-worktree                            mainporcelain
 git-write-tree                          plumbingmanipulators

git.c

@@ -705,6 +705,7 @@ static struct cmd_struct commands[] = {
 	{ "verify-pack", cmd_verify_pack },
 	{ "verify-tag", cmd_verify_tag, RUN_SETUP },
 	{ "version", cmd_version },
+	{ "virtualization", cmd_virtualization, RUN_SETUP | NEED_WORK_TREE },
 	{ "whatchanged", cmd_whatchanged, RUN_SETUP },
 	{ "worktree", cmd_worktree, RUN_SETUP },
 	{ "write-tree", cmd_write_tree, RUN_SETUP },

t/t1093-virtualfilesystem.sh

@@ -89,6 +89,17 @@ test_expect_success 'verify skip-worktree bit is set for absolute path' '
 	test_cmp expected actual
 '
 
+test_expect_success 'verify hydration percentage' '
+	git virtualization >actual &&
+	cat >expected <<-\EOF &&
+		Skipped: 3
+		Hydrated: 1
+		Total: 4
+		Hydration: 25.00%
+	EOF
+	test_cmp expected actual
+'
+
 test_expect_success 'verify skip-worktree bit is cleared for absolute path' '
 	clean_repo &&
 	write_script .git/hooks/virtualfilesystem <<-\EOF &&