t: add a test helper to truncate files

In a future commit, we're going to work with some large files which will
be at least 4 GiB in size.  To take advantage of the sparseness
functionality on most Unix systems and avoid running the system out of
disk, it would be convenient to use truncate(2) to simply create a
sparse file of sufficient size.

However, the GNU truncate(1) utility isn't portable, so let's write a
tiny test helper that does the work for us.

Signed-off-by: brian m. carlson <bk2204@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

4 files changed, 28 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 5776309365..3a6889d2bc 100644
--- a/Makefile
+++ b/Makefile
@@ -852,6 +852,7 @@ TEST_BUILTINS_OBJS += test-submodule-nested-repo-config.o
 TEST_BUILTINS_OBJS += test-submodule.o
 TEST_BUILTINS_OBJS += test-subprocess.o
 TEST_BUILTINS_OBJS += test-trace2.o
+TEST_BUILTINS_OBJS += test-truncate.o
 TEST_BUILTINS_OBJS += test-urlmatch-normalization.o
 TEST_BUILTINS_OBJS += test-userdiff.o
 TEST_BUILTINS_OBJS += test-wildmatch.o
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index abe8a785eb..9bd223b365 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -86,6 +86,7 @@ static struct test_cmd cmds[] = {
 	{ "submodule-nested-repo-config", cmd__submodule_nested_repo_config },
 	{ "subprocess", cmd__subprocess },
 	{ "trace2", cmd__trace2 },
+	{ "truncate", cmd__truncate },
 	{ "userdiff", cmd__userdiff },
 	{ "urlmatch-normalization", cmd__urlmatch_normalization },
 	{ "xml-encode", cmd__xml_encode },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index ea2672436c..f41a4d0aa8 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -79,6 +79,7 @@ int cmd__submodule_config(int argc, const char **argv);
 int cmd__submodule_nested_repo_config(int argc, const char **argv);
 int cmd__subprocess(int argc, const char **argv);
 int cmd__trace2(int argc, const char **argv);
+int cmd__truncate(int argc, const char **argv);
 int cmd__userdiff(int argc, const char **argv);
 int cmd__urlmatch_normalization(int argc, const char **argv);
 int cmd__xml_encode(int argc, const char **argv);
diff --git a/t/helper/test-truncate.c b/t/helper/test-truncate.c
new file mode 100644
index 0000000000..3931deaec7
--- /dev/null
+++ b/t/helper/test-truncate.c
@@ -0,0 +1,25 @@
+#include "test-tool.h"
+#include "git-compat-util.h"
+
+/*
+ * Truncate a file to the given size.
+ */
+int cmd__truncate(int argc, const char **argv)
+{
+	char *p = NULL;
+	uintmax_t sz = 0;
+	int fd = -1;
+
+	if (argc != 3)
+		die("expected filename and size");
+
+	sz = strtoumax(argv[2], &p, 0);
+	if (*p)
+		die("invalid size");
+
+	fd = xopen(argv[1], O_WRONLY | O_CREAT, 0600);
+
+	if (ftruncate(fd, (off_t) sz) < 0)
+		die_errno("failed to truncate file");
+	return 0;
+}