RFC settings & nvram.bin save setting to tmp file save old

save to a .tmp file on save and rename on next load

I think this should pretty minimally invasive as the same file
still gets overwritten in subsequent attempts until it is loaded again

the save path is still static
so it won't cause issues holding up shutdown.

load might be a bit slower with the searching for tmp+current file
and renaming them

Plus there is now a backup of your last settings file

Change-Id: If95618b93a0ba7954d5d8cab1d6ea3f07e658509

apps/settings.c

@@ -96,6 +96,29 @@ struct system_status global_status;
 #include "usb-ibasso.h"
 #endif
 
+#ifdef ROCKBOX_NO_TEMP_SETTINGS_FILE /* Overwrites same file each time */
+#define CONFIGFILE_TEMP CONFIGFILE
+#define NVRAM_FILE_TEMP NVRAM_FILE
+#define rename_temp_file(a,b,c)
+#else /* creates temp files on save, renames next load, saves old file if desired */
+#define CONFIGFILE_TEMP CONFIGFILE".new"
+#define NVRAM_FILE_TEMP NVRAM_FILE".new"
+static void rename_temp_file(const char *tempfile,
+                            const char *file,
+                            const char *oldfile)
+{
+    /* if tempfile does not exist -- Return
+     * if oldfile is supplied     -- Rename file to oldfile
+     * if tempfile does exist     -- Rename tempfile to file
+    */
+    if (file_exists(tempfile))
+    {
+        if (oldfile != NULL && file_exists(file))
+            rename(file, oldfile);
+        rename(tempfile, file);
+    }
+}
+#endif
 
 long lasttime = 0;
 
@@ -112,6 +135,7 @@ static char nvram_buffer[NVRAM_BLOCK_SIZE];
 
 static bool read_nvram_data(char* buf, int max_len)
 {
+    rename_temp_file(NVRAM_FILE_TEMP, NVRAM_FILE, NVRAM_FILE".old");
     unsigned crc32 = 0xffffffff;
     int var_count = 0, i = 0, buf_pos = 0;
     int fd = open(NVRAM_FILE, O_RDONLY);
@@ -182,7 +206,7 @@ static bool write_nvram_data(char* buf, int max_len)
     crc32 = crc_32(&buf[NVRAM_DATA_START],
                     max_len-NVRAM_DATA_START-1,0xffffffff);
     memcpy(&buf[4],&crc32,4);
-    fd = open(NVRAM_FILE,O_CREAT|O_TRUNC|O_WRONLY, 0666);
+    fd = open(NVRAM_FILE_TEMP,O_CREAT|O_TRUNC|O_WRONLY, 0666);
     if (fd >= 0)
     {
         int len = write(fd,buf,max_len);
@@ -203,6 +227,7 @@ void settings_load(int which)
         read_nvram_data(nvram_buffer,NVRAM_BLOCK_SIZE);
     if (which&SETTINGS_HD)
     {
+        rename_temp_file(CONFIGFILE_TEMP, CONFIGFILE, CONFIGFILE".old");
         settings_load_config(CONFIGFILE, false);
         settings_load_config(FIXEDSETTINGSFILE, false);
     }
@@ -571,7 +596,7 @@ static void flush_global_status_callback(void)
 static void flush_config_block_callback(void)
 {
     write_nvram_data(nvram_buffer,NVRAM_BLOCK_SIZE);
-    settings_write_config(CONFIGFILE, SETTINGS_SAVE_CHANGED);
+    settings_write_config(CONFIGFILE_TEMP, SETTINGS_SAVE_CHANGED);
 }
 
 void reset_runtime(void) {
@@ -609,6 +634,11 @@ int settings_save(void)
 
 bool settings_save_config(int options)
 {
+    /* if we have outstanding temp files it would be a good idea to flush
+     them before the user starts saving things */
+    rename_temp_file(NVRAM_FILE_TEMP, NVRAM_FILE, NULL); /* dont overwrite .old */
+    rename_temp_file(CONFIGFILE_TEMP, CONFIGFILE, NULL); /* files from last boot */
+
     char filename[MAX_PATH];
     const char *folder, *namebase;
     switch (options)