libfile: implement a function to cache a file

Due to the nature of TFTP which can't lseek and due to the silliness
of our filesystem implementation which can't cache accesses we have to
manually cache files on TFTP filesystems sometimes. Make it easier
for them by providing a cache_file() function which copies the file
from TFTP to RAM.

Signed-off-by: Sascha Hauer <[email protected]>

include/libfile.h

@@ -28,4 +28,6 @@ int unlink_recursive(const char *path, char **failedpath);
 
 char *make_temp(const char *template);
 
+int cache_file(const char *path, char **newpath);
+
 #endif /* __LIBFILE_H */

lib/libfile.c

@@ -496,7 +496,7 @@ int open_and_lseek(const char *filename, int mode, loff_t pos)
  * create a unique filename.
  *
  * Return: This function returns a filename which can be used as a temporary
- *         file lateron. The returned filename must be freed by the caller.
+ *         file later on. The returned filename must be freed by the caller.
  */
 char *make_temp(const char *template)
 {
@@ -512,3 +512,31 @@ char *make_temp(const char *template)
 
 	return name;
 }
+
+/**
+ * cache_file - Cache a file in /tmp
+ * @path:	The file to cache
+ * @newpath:	The return path where the file is copied to
+ *
+ * This function copies a given file to /tmp and returns its name in @newpath.
+ * @newpath is dynamically allocated and must be freed by the caller.
+ *
+ * Return: 0 for success, negative error code otherwise.
+ */
+int cache_file(const char *path, char **newpath)
+{
+	char *npath;
+	int ret;
+
+	npath = make_temp("filecache");
+
+	ret = copy_file(path, npath, 0);
+	if (ret) {
+		free(npath);
+		return ret;
+	}
+
+	*newpath = npath;
+
+	return 0;
+}