From 6557f07325409d769f414035cca05a563418e729 Mon Sep 17 00:00:00 2001
From: Jeremy Kerr <jk@ozlabs.org>
Date: Thu, 8 Aug 2013 15:25:24 +0800
Subject: discover/file: Add replace_file()

Add a function to atomically replace a file.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
---
 discover/file.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 discover/file.h |  1 +
 2 files changed, 44 insertions(+)

(limited to 'discover')

diff --git a/discover/file.c b/discover/file.c
index 269421c..1ebfe43 100644
--- a/discover/file.c
+++ b/discover/file.c
@@ -17,6 +17,8 @@
 
 #include <fcntl.h>
 #include <unistd.h>
+#include <stdlib.h>
+#include <errno.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 
@@ -75,3 +77,44 @@ err_close:
 	close(fd);
 	return -1;
 }
+
+static int write_fd(int fd, char *buf, int len)
+{
+	int i, rc;
+
+	for (i = 0; i < len; i += rc) {
+		rc = write(fd, buf + i, len - i);
+		if (rc < 0 && errno != -EINTR)
+			return rc;
+	}
+
+	return 0;
+}
+
+int replace_file(const char *filename, char *buf, int len)
+{
+	char *tempfile;
+	mode_t oldmask;
+	int rc, fd;
+
+	tempfile = talloc_asprintf(NULL, "%s.XXXXXX", filename);
+
+	oldmask = umask(0644);
+	fd = mkstemp(tempfile);
+	umask(oldmask);
+	if (fd < 0) {
+		free(tempfile);
+		return fd;
+	}
+
+	rc = write_fd(fd, buf, len);
+	if (rc) {
+		unlink(tempfile);
+	} else {
+		rc = rename(tempfile, filename);
+	}
+
+	free(tempfile);
+	close(fd);
+	return rc;
+}
diff --git a/discover/file.h b/discover/file.h
index 1997eca..8aa7d3c 100644
--- a/discover/file.h
+++ b/discover/file.h
@@ -18,6 +18,7 @@
 #define FILE_H
 
 int read_file(void *ctx, const char *filename, char **bufp, int *lenp);
+int replace_file(const char *filename, char *buf, int len);
 
 #endif /* FILE_H */
 
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