From: Derrick Stolee <dstolee@microsoft.com>
Date: Mon, 21 Oct 2019 13:56:25 +0000 (+0000)
Subject: sparse-checkout: write using lockfile
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=a879c5bfb5738d7f8468af1f9b02f12e6bb73c38;p=git

sparse-checkout: write using lockfile

If two 'git sparse-checkout set' subcommands are launched at the
same time, the behavior can be unexpected as they compete to write
the sparse-checkout file and update the working directory.

Take a lockfile around the writes to the sparse-checkout file. In
addition, acquire this lock around the working directory update
to avoid two commands updating the working directory in different
ways.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index ea2e7ee51b..76f65d8edd 100644
--- a/builtin/sparse-checkout.c
+++ b/builtin/sparse-checkout.c
@@ -306,25 +306,34 @@ static int write_patterns_and_update(struct pattern_list *pl)
 {
 	char *sparse_filename;
 	FILE *fp;
+	int fd;
+	struct lock_file lk = LOCK_INIT;
 	int result;
 
 	result = update_working_directory(pl);
 
+	sparse_filename = get_sparse_checkout_filename();
+	fd = hold_lock_file_for_update(&lk, sparse_filename,
+				      LOCK_DIE_ON_ERROR);
+
+	result = update_working_directory(pl);
 	if (result) {
+		rollback_lock_file(&lk);
+		free(sparse_filename);
 		clear_pattern_list(pl);
 		update_working_directory(NULL);
 		return result;
 	}
 
-	sparse_filename = get_sparse_checkout_filename();
-	fp = fopen(sparse_filename, "w");
+	fp = xfdopen(fd, "w");
 
 	if (core_sparse_checkout_cone)
 		write_cone_to_file(fp, pl);
 	else
 		write_patterns_to_file(fp, pl);
 
-	fclose(fp);
+	fflush(fp);
+	commit_lock_file(&lk);
 
 	free(sparse_filename);
 	clear_pattern_list(pl);
diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
index a580b79595..2db706a9e4 100755
--- a/t/t1091-sparse-checkout-builtin.sh
+++ b/t/t1091-sparse-checkout-builtin.sh
@@ -276,4 +276,11 @@ test_expect_success 'revert to old sparse-checkout on empty update' '
 	)
 '
 
+test_expect_success 'fail when lock is taken' '
+	test_when_finished rm -rf repo/.git/info/sparse-checkout.lock &&
+	touch repo/.git/info/sparse-checkout.lock &&
+	test_must_fail git -C repo sparse-checkout set deep 2>err &&
+	test_i18ngrep "File exists" err
+'
+
 test_done