[PATCH v2 1/2] t: add a test helper to truncate files

["brian m. carlson" <sandals@xxxxxxxxxxxxxxxxxxxx>]

From: "brian m. carlson" <bk2204@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 Makefile                 |  1 +
 t/helper/test-tool.c     |  1 +
 t/helper/test-tool.h     |  1 +
 t/helper/test-truncate.c | 27 +++++++++++++++++++++++++++
 4 files changed, 30 insertions(+)
 create mode 100644 t/helper/test-truncate.c

diff --git a/Makefile b/Makefile
index 9c6a2f125f..03adcb5a48 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 9010ac6de7..876cd2dc31 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 f134f96b97..70dd4eba11 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..bd3fde364b
--- /dev/null
+++ b/t/helper/test-truncate.c
@@ -0,0 +1,27 @@
+#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 = open(argv[1], O_WRONLY | O_CREAT, 0600);
+	if (fd < 0)
+		die_errno("failed to open file %s", argv[1]);
+
+	if (ftruncate(fd, (off_t) sz) < 0)
+		die_errno("failed to truncate file");
+	return 0;
+}