3720a61da
Denys Vlasenko
2016-10-09
Subject
ifupdown: rewrite state file atomically
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Commit Diff GitHub →
networking/ifupdown.c+38 -5
| @@ -56,6 +56,7 @@ | |
| #endif | |
| #define UDHCPC_CMD_OPTIONS CONFIG_IFUPDOWN_UDHCPC_CMD_OPTIONS | |
| + | #define IFSTATE_FILE_PATH CONFIG_IFUPDOWN_IFSTATE_PATH |
| #define debug_noise(args...) /*fprintf(stderr, args)*/ | |
| @@ -1200,7 +1201,7 @@ static llist_t *find_iface_state(llist_t *state_list, const char *iface) | |
| static llist_t *read_iface_state(void) | |
| { | |
| llist_t *state_list = NULL; | |
| - | FILE *state_fp = fopen_for_read(CONFIG_IFUPDOWN_IFSTATE_PATH); |
| + | FILE *state_fp = fopen_for_read(IFSTATE_FILE_PATH); |
| if (state_fp) { | |
| char *start, *end_ptr; | |
| @@ -1215,6 +1216,38 @@ static llist_t *read_iface_state(void) | |
| return state_list; | |
| } | |
| + | /* read the previous state from the state file */ |
| + | static FILE *open_new_state_file(void) |
| + | { |
| + | int fd, flags, cnt; |
| + | |
| + | cnt = 0; |
| + | flags = (O_WRONLY | O_CREAT | O_EXCL); |
| + | for (;;) { |
| + | fd = open(IFSTATE_FILE_PATH".new", flags, 0666); |
| + | if (fd >= 0) |
| + | break; |
| + | if (errno != EEXIST |
| + | || flags == (O_WRONLY | O_CREAT | O_TRUNC) |
| + | ) { |
| + | bb_perror_msg_and_die("can't open '%s'", |
| + | IFSTATE_FILE_PATH".new"); |
| + | } |
| + | /* Someone else created the .new file */ |
| + | if (cnt > 30 * 1000) { |
| + | /* Waited for 30*30/2 = 450 milliseconds, still EEXIST. |
| + | * Assuming a stale file, rewriting it. |
| + | */ |
| + | flags = (O_WRONLY | O_CREAT | O_TRUNC); |
| + | continue; |
| + | } |
| + | usleep(cnt); |
| + | cnt += 1000; |
| + | } |
| + | |
| + | return xfdopen_for_write(fd); |
| + | } |
| + | |
| int ifupdown_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; | |
| int ifupdown_main(int argc UNUSED_PARAM, char **argv) | |
| @@ -1348,7 +1381,7 @@ int ifupdown_main(int argc UNUSED_PARAM, char **argv) | |
| any_failures = 1; | |
| } else if (!NO_ACT) { | |
| /* update the state file */ | |
| - | FILE *state_fp; |
| + | FILE *new_state_fp = open_new_state_file(); |
| llist_t *state; | |
| llist_t *state_list = read_iface_state(); | |
| llist_t *iface_state = find_iface_state(state_list, iface); | |
| @@ -1368,15 +1401,15 @@ int ifupdown_main(int argc UNUSED_PARAM, char **argv) | |
| } | |
| /* Actually write the new state */ | |
| - | state_fp = xfopen_for_write(CONFIG_IFUPDOWN_IFSTATE_PATH); |
| state = state_list; | |
| while (state) { | |
| if (state->data) { | |
| - | fprintf(state_fp, "%s\n", state->data); |
| + | fprintf(new_state_fp, "%s\n", state->data); |
| } | |
| state = state->link; | |
| } | |
| - | fclose(state_fp); |
| + | fclose(new_state_fp); |
| + | xrename(IFSTATE_FILE_PATH".new", IFSTATE_FILE_PATH); |
| llist_free(state_list, free); | |
| } | |
| next: | |