Reset tail offset by -1 when starting and resetting journal pointer.

Our journald API usage was incorrect causing our tail pointer to stick
after the last received entry, causing us to receive no additional
events at all.

The `sd_journal_next` API states that we should always assume that we
reset to the previous entry after `sd_journal_seek_tail` and this
corrects the behavior that many are seeing where tallow just isn't doing
anything at all.

This addresses clearlinux#25 from clearlinux/tallow. Tested on F41.

Signed-off-by: Auke Kok <[email protected]>

src/tallow.c

@@ -372,6 +372,7 @@ int main(void)
 
 	/* go to the tail and wait */
 	r = sd_journal_seek_tail(j);
+	sd_journal_previous(j);
 	sd_journal_wait(j, (uint64_t) 0);
 	dbg("sd_journal_seek_tail() returned %d\n", r);
 	while (sd_journal_next(j) != 0)
@@ -388,6 +389,7 @@ int main(void)
 		if (r == SD_JOURNAL_INVALIDATE) {
 			fprintf(stderr, "Journal was rotated, resetting\n");
 			sd_journal_seek_tail(j);
+			sd_journal_previous(j);
 		} else if (r == SD_JOURNAL_NOP) {
 			dbg("Timeout reached, waiting again\n");
 			continue;
@@ -418,6 +420,8 @@ int main(void)
 			m = strndup(d, l+1);
 			m[l] = '\0';
 
+			dbg("msg %s\n", m);
+
 			struct pattern_struct *pat = patterns;
 			while (pat) {
 				int off[MAX_OFFSETS];