journal: defer journal closes on rotate

When we rotate journals, we must set offline and close the current one,
but don't generally need to wait for this to complete.

Instead, we'll initiate an asynchronous offline via
journal_file_set_offline(oldfile, false), and add the file to a
per-server set of deferred closes to be closed later when they
won't block.

There's one complication however; journal_file_open() via
journal_file_verify_header() assumes that any writable journal in the
online state is the product of an unclean shutdown or other form of
corruption.

Thus there's a need for journal_file_open() to be aware of deferred
closes and synchronize with their completion when opening preexisting
journals for writing.  To facilitate this the deferred closes set is
supplied to the journal_file_open() function where the deferred closes
may be closed synchronously before verifying the header in such
circumstances.

1 files changed, 19 insertions, 3 deletions

diff --git a/src/journal/journald-server.c b/src/journal/journald-server.c
index ac992a8b54..d5937bd013 100644
--- a/src/journal/journald-server.c
+++ b/src/journal/journald-server.c
@@ -251,9 +251,9 @@ static int open_journal(
         assert(ret);
 
         if (reliably)
-                r = journal_file_open_reliably(fname, flags, 0640, s->compress, seal, metrics, s->mmap, NULL, &f);
+                r = journal_file_open_reliably(fname, flags, 0640, s->compress, seal, metrics, s->mmap, s->deferred_closes, NULL, &f);
         else
-                r = journal_file_open(fname, flags, 0640, s->compress, seal, metrics, s->mmap, NULL, &f);
+                r = journal_file_open(fname, flags, 0640, s->compress, seal, metrics, s->mmap, s->deferred_closes, NULL, &f);
         if (r < 0)
                 return r;
 
@@ -333,7 +333,7 @@ static int do_rotate(
         if (!*f)
                 return -EINVAL;
 
-        r = journal_file_rotate(f, s->compress, seal);
+        r = journal_file_rotate(f, s->compress, seal, s->deferred_closes);
         if (r < 0)
                 if (*f)
                         log_error_errno(r, "Failed to rotate %s: %m", (*f)->path);
@@ -364,6 +364,13 @@ void server_rotate(Server *s) {
                         /* Old file has been closed and deallocated */
                         ordered_hashmap_remove(s->user_journals, k);
         }
+
+        /* Perform any deferred closes which aren't still offlining. */
+        SET_FOREACH(f, s->deferred_closes, i)
+                if (!journal_file_is_offlining(f)) {
+                        (void) set_remove(s->deferred_closes, f);
+                        (void) journal_file_close(f);
+                }
 }
 
 void server_sync(Server *s) {
@@ -1765,6 +1772,10 @@ int server_init(Server *s) {
         if (!s->mmap)
                 return log_oom();
 
+        s->deferred_closes = set_new(NULL);
+        if (!s->deferred_closes)
+                return log_oom();
+
         r = sd_event_default(&s->event);
         if (r < 0)
                 return log_error_errno(r, "Failed to create event loop: %m");
@@ -1918,6 +1929,11 @@ void server_done(Server *s) {
         JournalFile *f;
         assert(s);
 
+        if (s->deferred_closes) {
+                journal_file_close_set(s->deferred_closes);
+                set_free(s->deferred_closes);
+        }
+
         while (s->stdout_streams)
                 stdout_stream_free(s->stdout_streams);