journal: when we encounter a broken journal file, add some debug logging

Let's make it easier to figure out when we see an invalid journal file, why we
consider it invalid, and add some minimal debug logging for it.

This log output is normally not seen (after all, this all is library code),
unless debug logging is exlicitly turned on.

2 files changed, 21 insertions, 7 deletions

diff --git a/src/journal/journal-file.c b/src/journal/journal-file.c
index 349ef74e81..953f4e5ce6 100644
--- a/src/journal/journal-file.c
+++ b/src/journal/journal-file.c
@@ -747,12 +747,16 @@ int journal_file_move_to_object(JournalFile *f, ObjectType type, uint64_t offset
         assert(ret);
 
         /* Objects may only be located at multiple of 64 bit */
-        if (!VALID64(offset))
+        if (!VALID64(offset)) {
+                log_debug("Attempt to move to object at non-64bit boundary: %" PRIu64, offset);
                 return -EBADMSG;
+        }
 
         /* Object may not be located in the file header */
-        if (offset < le64toh(f->header->header_size))
+        if (offset < le64toh(f->header->header_size)) {
+                log_debug("Attempt to move to object located in file header: %" PRIu64, offset);
                 return -EBADMSG;
+        }
 
         r = journal_file_move_to(f, type, false, offset, sizeof(ObjectHeader), &t);
         if (r < 0)
@@ -761,17 +765,25 @@ int journal_file_move_to_object(JournalFile *f, ObjectType type, uint64_t offset
         o = (Object*) t;
         s = le64toh(o->object.size);
 
-        if (s < sizeof(ObjectHeader))
+        if (s < sizeof(ObjectHeader)) {
+                log_debug("Attempt to move to overly short object: %" PRIu64, offset);
                 return -EBADMSG;
+        }
 
-        if (o->object.type <= OBJECT_UNUSED)
+        if (o->object.type <= OBJECT_UNUSED) {
+                log_debug("Attempt to move to object with invalid type: %" PRIu64, offset);
                 return -EBADMSG;
+        }
 
-        if (s < minimum_header_size(o))
+        if (s < minimum_header_size(o)) {
+                log_debug("Attempt to move to truncated object: %" PRIu64, offset);
                 return -EBADMSG;
+        }
 
-        if (type > OBJECT_UNUSED && o->object.type != type)
+        if (type > OBJECT_UNUSED && o->object.type != type) {
+                log_debug("Attempt to move to object of unexpected type: %" PRIu64, offset);
                 return -EBADMSG;
+        }
 
         if (s > sizeof(ObjectHeader)) {
                 r = journal_file_move_to(f, type, false, offset, s, &t);
diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index 13e3b44f06..f753435888 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -1091,8 +1091,10 @@ static int discover_next_boot(sd_journal *j,
                 r = sd_journal_previous(j);
         if (r < 0)
                 return r;
-        else if (r == 0)
+        else if (r == 0) {
+                log_debug("Whoopsie! We found a boot ID but can't read its last entry.");
                 return -ENODATA; /* This shouldn't happen. We just came from this very boot ID. */
+        }
 
         r = sd_journal_get_realtime_usec(j, &next_boot->last);
         if (r < 0)