From 749f6041a00b218a7d1fe668fa5efd455563e92e Mon Sep 17 00:00:00 2001
From: =?utf8?q?Kristian=20H=C3=B8gsberg?= <krh@redhat.com>
Date: Mon, 7 Apr 2008 00:31:01 -0400
Subject: [PATCH] Create the new repo file O_EXCL to prevent racing with another razor process.

And remember to clean it up on exit paths.
---
 main.c  |   38 ++++++++++++++++++++++++++++----------
 razor.c |   28 ++++++++++++++++++++--------
 razor.h |    1 +
 3 files changed, 49 insertions(+), 18 deletions(-)

diff --git a/main.c b/main.c
index 6bcd996..a2ef1d0 100644
--- a/main.c
+++ b/main.c
@@ -5,6 +5,7 @@
 #include <string.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include <fcntl.h>
 #include <dirent.h>
 #include <curl/curl.h>
 #include <fnmatch.h>
@@ -530,33 +531,50 @@ command_install(int argc, const char *argv[])
 	struct razor_transaction *trans;
 	char path[PATH_MAX], new_path[PATH_MAX];
 	CURL *curl;
-	int errors;
+	int errors, fd;
+
+	/* Create the new next repo file up front to ensure exclusive
+	 * access. */
+	snprintf(new_path, sizeof new_path,
+		 "%s%s/%s", root, razor_root_path, next_repo_filename);
+	fd = open(new_path, O_CREAT | O_WRONLY | O_TRUNC | O_EXCL, 0666);
+	if (fd < 0) {
+		fprintf(stderr, "failed to get lock file, "
+			"maybe previous operation crashed?\n");
+
+		/* FIXME: Use fcntl advisory locking to figure out
+		 * whether previous operation crashed or is still in
+		 * progress. */
+
+		return -1;
+	}
 
 	upstream = razor_set_open(rawhide_repo_filename);
 	snprintf(path, sizeof path,
 		 "%s%s/%s", root, razor_root_path, system_repo_filename);
 	system = razor_set_open(path);
-	if (system == NULL || upstream == NULL)
+	if (system == NULL || upstream == NULL) {
+		unlink(new_path);
 		return 1;
+	}
 	trans = razor_transaction_create(system, upstream,
 					 argc, argv, 0, NULL);
 	errors = razor_transaction_describe(trans);
-	if (errors)
+	if (errors) {
+		unlink(new_path);
 		return 1;
+	}
 
 	next = razor_transaction_finish(trans);
 
-	/* FIXME: Need razor_set_write_to_fd() so we can open it excl
-	 * up front here or fail if it already exists. */
-	snprintf(new_path, sizeof new_path,
-		 "%s%s/%s", root, razor_root_path, next_repo_filename);
-
-	razor_set_write(next, new_path);
+	razor_set_write_to_fd(next, fd);
 	printf("wrote %s\n", new_path);
 
 	curl = curl_easy_init();
-	if (curl == NULL)
+	if (curl == NULL) {
+		unlink(new_path);
 		return 1;
+	}
 	razor_set_diff(system, next, download_package, curl);	
 	curl_easy_cleanup(curl);
 
diff --git a/razor.c b/razor.c
index 5e77402..722f41b 100644
--- a/razor.c
+++ b/razor.c
@@ -198,13 +198,13 @@ razor_set_destroy(struct razor_set *set)
 }
 
 int
-razor_set_write(struct razor_set *set, const char *filename)
+razor_set_write_to_fd(struct razor_set *set, int fd)
 {
 	char data[4096];
 	struct razor_set_header *header = (struct razor_set_header *) data;
 	struct array *a;
 	uint32_t offset;
-	int i, fd;
+	int i;
 
 	memset(data, 0, sizeof data);
 	header->magic = RAZOR_MAGIC;
@@ -225,10 +225,6 @@ razor_set_write(struct razor_set *set, const char *filename)
 	header->sections[i].offset = 0;
 	header->sections[i].size = 0;
 
-	fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC, 0666);
-	if (fd < 0)
-		return -1;
-
 	razor_write(fd, data, sizeof data);
 	memset(data, 0, sizeof data);
 	for (i = 0; i < ARRAY_SIZE(razor_sections); i++) {
@@ -239,11 +235,27 @@ razor_set_write(struct razor_set *set, const char *filename)
 		razor_write(fd, data, ALIGN(a->size, 4096) - a->size);
 	}
 
-	close(fd);
-
 	return 0;
 }
 
+int
+razor_set_write(struct razor_set *set, const char *filename)
+{
+	int fd, status;
+
+	fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC, 0666);
+	if (fd < 0)
+		return -1;
+
+	status = razor_set_write_to_fd(set, fd);
+	if (status) {
+	    close(fd);
+	    return status;
+	}
+
+	return close(fd);
+}
+
 void
 razor_build_evr(char *evr_buf, int size, const char *epoch,
 		const char *version, const char *release)
diff --git a/razor.h b/razor.h
index cc6a869..62e8e5f 100644
--- a/razor.h
+++ b/razor.h
@@ -26,6 +26,7 @@ extern const char * const razor_version_relations[];
 struct razor_set *razor_set_create(void);
 struct razor_set *razor_set_open(const char *filename);
 void razor_set_destroy(struct razor_set *set);
+int razor_set_write_to_fd(struct razor_set *set, int fd);
 int razor_set_write(struct razor_set *set, const char *filename);
 
 struct razor_package *
-- 
1.7.1