From f3984a9b4fb17c12956138694936c62959ebec2d Mon Sep 17 00:00:00 2001
From: Tobias Wiese <tobias@tobiaswiese.com>
Date: Sat, 21 Mar 2020 02:47:36 +0100
Subject: Initial Commit

The application exchanges 2 files, given as arguments.

Signed-off-by: Tobias Wiese <tobias@tobiaswiese.com>
---
 .gitignore     |   3 ++
 Makefile       |   9 +++++
 README         |   4 +++
 src/Makefile   |  19 +++++++++++
 src/exchange.c | 103 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 138 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 README
 create mode 100644 src/Makefile
 create mode 100644 src/exchange.c

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..6783a1d
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+*.[oa]
+*~
+/src/exchange
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..ec85e7e
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,9 @@
+SHELL   = /bin/sh
+
+.PHONY: all clean
+
+all:
+	@$(MAKE) -C src/
+
+clean:
+	@$(MAKE) -C src/ $@
diff --git a/README b/README
new file mode 100644
index 0000000..32b9783
--- /dev/null
+++ b/README
@@ -0,0 +1,4 @@
+# exchange
+
+A small tool that allows 2 files to be exchanged.
+This is done through the renameat2(2) syscall.
diff --git a/src/Makefile b/src/Makefile
new file mode 100644
index 0000000..972f55e
--- /dev/null
+++ b/src/Makefile
@@ -0,0 +1,19 @@
+CC      := gcc
+CFLAGS  := -Wall
+LDFLAGS :=
+
+CFLAGS  += -DVERSIN="\"$(shell git describe --dirty --always)\""
+
+TARGETS := exchange
+MAINS   := $(addsuffix .o, $(TARGETS))
+OBJ     := $(MAINS)
+
+.PHONY: all
+all: $(TARGETS)
+
+.PHONY: clean
+clean:
+	rm -rf $(OBJ) $(TARGETS)
+
+$(TARGETS): % : %.o
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^
diff --git a/src/exchange.c b/src/exchange.c
new file mode 100644
index 0000000..e525e8f
--- /dev/null
+++ b/src/exchange.c
@@ -0,0 +1,103 @@
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdio.h>
+#include <errno.h>
+#include <stdlib.h>
+
+#ifndef SMALL
+#include <getopt.h>
+#include <unistd.h>
+#endif
+
+#ifndef DEFAULT_PROGRAM_NAME
+# define DEFAULT_PROGRAM_NAME "exchange"
+#endif
+
+#ifndef VERSION
+# define VERSION ""
+#endif
+
+#ifndef SMALL
+static char *program_name = DEFAULT_PROGRAM_NAME;
+static struct option const long_options[] = {
+	{ "help", no_argument, NULL, 'h' },
+	{ "version", no_argument, NULL, 'v' },
+	{ NULL, 0, NULL, 0 },
+};
+
+void usage(FILE *fd) {
+	fprintf(fd, "\
+Usage: %s [OPTION]... <PATH 1> <PATH 2>\n\
+Exchange PATH 1 and PATH 2.\n",
+		program_name);
+	fputs("\n", fd);
+	fputs("\
+Available Options:\n\
+  -h, --help            display this help and exit\n\
+  -v, --version         output version information and exit\n", fd);
+}
+
+void version() {
+	printf("%s %s\n", program_name, VERSION);
+	printf("Build on %s %s.\n", __DATE__, __TIME__);
+}
+#endif // !SMALL
+
+int main(int argc, char *argv[]) {
+	char *path1, *path2;
+#ifndef SMALL
+	if (argc > 0)
+		program_name = argv[0];
+
+	int c;
+	while ((c = getopt_long(argc, argv, "hvt", long_options, NULL))
+			!= -1)
+	{
+		switch (c) {
+			case 't':
+				break;
+			case 'h':  // help
+				usage(stdout);
+				return EXIT_SUCCESS;
+			case 'v':  // version
+				version();
+				return EXIT_SUCCESS;
+			default:
+				usage(stderr);
+				return EXIT_FAILURE;
+		}
+	}
+
+	if (argc - optind != 2) {
+		fprintf(stderr, "%s: invalid number of arguments. Expected 2.\n", program_name);
+		usage(stderr);
+		return EXIT_FAILURE;
+	}
+
+#else
+	// We currently don't accept any options
+	// when compiling with SMALL
+	// Define optind manually, because we don't use optparse.
+	const int optind = 1;
+#endif // !SMALL
+
+	if (argc - optind != 2) {
+#ifndef SMALL
+		fprintf(stderr, "%s: invalid number of arguments. Expected 2.\n", program_name);
+		usage(stderr);
+#endif
+		return EXIT_FAILURE;
+	}
+	path1 = argv[optind];
+	path2 = argv[optind + 1];
+
+	// Do the magic
+	if (renameat2(AT_FDCWD, path1, AT_FDCWD, path2, RENAME_EXCHANGE) != 0) {
+		int errsv = errno;
+#ifndef SMALL
+		perror(program_name);
+#endif
+		return -errsv;
+	}
+	return EXIT_SUCCESS;
+}
-- 
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