sd-journal: do not reset sd_j_enumerate_unique position on error

systemctl would call sd_j_enumerate_unique() interleaved with
sd_j_next(). But the latter can remove a file if it detects an
error in it. In those circumstances sd_j_enumerate_unique would
restart with the first file in hashmap. With many corrupted files
sd_j_enumerate_unique might iterate over the list multiple times.

Avoid this by jumping to the next file in unique list if possible,
or setting a flag that tells sd_j_enumerate_unique that it is done
otherwise.

1 files changed, 12 insertions, 6 deletions

diff --git a/src/journal/sd-journal.c b/src/journal/sd-journal.c
index 1fc9f01d0a..b72a0867e7 100644
--- a/src/journal/sd-journal.c
+++ b/src/journal/sd-journal.c
@@ -1375,8 +1375,11 @@ static void remove_file_real(sd_journal *j, JournalFile *f) {
         }
 
         if (j->unique_file == f) {
-                j->unique_file = NULL;
+                /* Jump to the next unique_file or NULL if that one was last */
+                j->unique_file = hashmap_next(j->files, j->unique_file->path);
                 j->unique_offset = 0;
+                if (!j->unique_file)
+                        j->unique_file_lost = true;
         }
 
         journal_file_close(f);
@@ -2490,6 +2493,7 @@ _public_ int sd_journal_query_unique(sd_journal *j, const char *field) {
         j->unique_field = f;
         j->unique_file = NULL;
         j->unique_offset = 0;
+        j->unique_file_lost = false;
 
         return 0;
 }
@@ -2506,9 +2510,13 @@ _public_ int sd_journal_enumerate_unique(sd_journal *j, const void **data, size_
         k = strlen(j->unique_field);
 
         if (!j->unique_file) {
+                if (j->unique_file_lost)
+                        return 0;
+
                 j->unique_file = hashmap_first(j->files);
                 if (!j->unique_file)
                         return 0;
+
                 j->unique_offset = 0;
         }
 
@@ -2538,13 +2546,10 @@ _public_ int sd_journal_enumerate_unique(sd_journal *j, const void **data, size_
 
                 /* We reached the end of the list? Then start again, with the next file */
                 if (j->unique_offset == 0) {
-                        JournalFile *n;
-
-                        n = hashmap_next(j->files, j->unique_file->path);
-                        if (!n)
+                        j->unique_file = hashmap_next(j->files, j->unique_file->path);
+                        if (!j->unique_file)
                                 return 0;
 
-                        j->unique_file = n;
                         continue;
                 }
 
@@ -2632,6 +2637,7 @@ _public_ void sd_journal_restart_unique(sd_journal *j) {
 
         j->unique_file = NULL;
         j->unique_offset = 0;
+        j->unique_file_lost = false;
 }
 
 _public_ int sd_journal_reliable_fd(sd_journal *j) {