journald: always vacuum empty offline files

Corrupted empty files are relatively common. I think they are created
when a coredump for a user who never logged anything before is
attempted to be written, but the write does not succeed because the
coredump is too big, but there are probably other ways to create
those, especially if the machine crashes at the right time.
Non-corrupted empty files can also happen, e.g. if a journal file is
opened, but nothing is ever successfully written to it and it is
rotated because of MaxFileSec=. Either way, each "empty" journal file
costs around 3 MB, and there's little point in keeping them around.

diff --git a/src/journal/journal-vacuum.c b/src/journal/journal-vacuum.c
index 1ddb043e2cd13ccc0bbf4a70984455752382d1fe..79572f1fb6df556e25d09075afa5b5b265757462 100644 (file)
--- a/src/journal/journal-vacuum.c
+++ b/src/journal/journal-vacuum.c
@@ -128,6 +128,24 @@ static void patch_realtime(
 #endif
 }
 
+static int journal_file_empty(int dir_fd, const char *name) {
+        int fd, r;
+        le64_t n_entries;
+
+        fd = openat(dir_fd, name, O_RDONLY|O_CLOEXEC|O_NOFOLLOW|O_NONBLOCK);
+        if (fd < 0)
+                return -errno;
+
+        if (lseek(fd, offsetof(Header, n_entries), SEEK_SET) < 0)
+                return -errno;
+
+        r = read(fd, &n_entries, sizeof(n_entries));
+        if (r != sizeof(n_entries))
+                return r == 0 ? -EINVAL : -errno;
+
+        return le64toh(n_entries) == 0;
+}
+
 int journal_directory_vacuum(
                 const char *directory,
                 uint64_t max_use,
@@ -247,6 +265,17 @@ int journal_directory_vacuum(
                         /* We do not vacuum active files or unknown files! */
                         continue;
 
+                if (journal_file_empty(dirfd(d), de->d_name)) {
+
+                        /* Always vacuum empty non-online files. */
+
+                        if (unlinkat(dirfd(d), de->d_name, 0) >= 0)
+                                log_debug("Deleted empty journal %s/%s.", directory, de->d_name);
+                        else if (errno != ENOENT)
+                                log_warning("Failed to delete %s/%s: %m", directory, de->d_name);
+                        continue;
+                }
+
                 patch_realtime(directory, de->d_name, &st, &realtime);
 
                 GREEDY_REALLOC(list, n_allocated, n_list + 1);