test: make the diff regex BRE-compatible

Since the GNU `diff` utility uses grep-style regular expressions[0], which
use the BRE style, we need to tweak the regex to make it work properly
(most notably - in BRE the meta characters need to be escaped).

```
$ diff a b
21c21
<   Volume Key: 256bit
---
>   Volume Key: 257bit
25c25
< Disk Ceiling: 323.2M
---
> Disk Ceiling: 323.1M

$ diff -I '^\s*Disk (Size|Free|Floor|Ceiling):' a b
21c21
<   Volume Key: 256bit
---
>   Volume Key: 257bit
25c25
< Disk Ceiling: 323.2M
---
> Disk Ceiling: 323.1M

$ diff -I '^\s*Disk \(Size\|Free\|Floor\|Ceiling\):' a b && echo OK
21c21
<   Volume Key: 256bit
---
>   Volume Key: 257bit
```

Caught in one of the nightly CentOS CI cron jobs.

[0] https://www.gnu.org/software/diffutils/manual/html_node/Specified-Lines.html

src/basic/log.c

@@ -358,7 +358,7 @@ void log_forget_fds(void) {
 }
 
 void log_set_max_level(int level) {
-        assert((level & LOG_PRIMASK) == level);
+        assert(level == LOG_NULL || (level & LOG_PRIMASK) == level);
 
         log_max_level = level;
 }

src/basic/log.h

@@ -27,6 +27,10 @@ typedef enum LogTarget{
         _LOG_TARGET_INVALID = -EINVAL,
 } LogTarget;
 
+/* This log level disables logging completely. It can only be passed to log_set_max_level() and cannot be
+ * used a regular log level. */
+#define LOG_NULL (LOG_EMERG - 1)
+
 /* Note to readers: << and >> have lower precedence than & and | */
 #define SYNTHETIC_ERRNO(num)                (1 << 30 | (num))
 #define IS_SYNTHETIC_ERRNO(val)             ((val) >> 30 & 1)

src/journal/journald-kmsg.c

@@ -19,6 +19,7 @@
 #include "journald-kmsg.h"
 #include "journald-server.h"
 #include "journald-syslog.h"
+#include "log.h"
 #include "parse-util.h"
 #include "process-util.h"
 #include "stdio-util.h"
@@ -106,6 +107,8 @@ void dev_kmsg_record(Server *s, char *p, size_t l) {
         char *e, *f, *k;
         uint64_t serial;
         size_t pl;
+        int saved_log_max_level = INT_MAX;
+        ClientContext *c = NULL;
 
         assert(s);
         assert(p);
@@ -266,10 +269,16 @@ void dev_kmsg_record(Server *s, char *p, size_t l) {
         else {
                 pl -= syslog_parse_identifier((const char**) &p, &identifier, &pid);
 
-                /* Avoid any messages we generated ourselves via
+                /* Avoid logging any new messages when we're processing messages generated by ourselves via
-                 * log_info() and friends. */
+                 * log_info() and friends to avoid infinite loops. */
-                if (is_us(identifier, pid))
+                if (is_us(identifier, pid)) {
-                        goto finish;
+                        if (!ratelimit_below(&s->kmsg_own_ratelimit))
+                                return;
+
+                        saved_log_max_level = log_get_max_level();
+                        c = s->my_context;
+                        log_set_max_level(LOG_NULL);
+                }
 
                 if (identifier) {
                         syslog_identifier = strjoin("SYSLOG_IDENTIFIER=", identifier);
@@ -287,7 +296,11 @@ void dev_kmsg_record(Server *s, char *p, size_t l) {
         if (cunescape_length_with_prefix(p, pl, "MESSAGE=", UNESCAPE_RELAX, &message) >= 0)
                 iovec[n++] = IOVEC_MAKE_STRING(message);
 
-        server_dispatch_message(s, iovec, n, ELEMENTSOF(iovec), NULL, NULL, priority, 0);
+
+        server_dispatch_message(s, iovec, n, ELEMENTSOF(iovec), c, NULL, priority, 0);
+
+        if (saved_log_max_level != INT_MAX)
+                log_set_max_level(saved_log_max_level);
 
 finish:
         for (j = 0; j < z; j++)

src/journal/journald-server.c

@@ -65,6 +65,9 @@
 #define DEFAULT_RATE_LIMIT_BURST 10000
 #define DEFAULT_MAX_FILE_USEC USEC_PER_MONTH
 
+#define DEFAULT_KMSG_OWN_INTERVAL (5 * USEC_PER_SEC)
+#define DEFAULT_KMSG_OWN_BURST 50
+
 #define RECHECK_SPACE_USEC (30*USEC_PER_SEC)
 
 #define NOTIFY_SNDBUF_SIZE (8*1024*1024)
@@ -2212,6 +2215,11 @@ int server_init(Server *s, const char *namespace) {
 
                 .runtime_storage.name = "Runtime Journal",
                 .system_storage.name = "System Journal",
+
+                .kmsg_own_ratelimit = {
+                        .interval = DEFAULT_KMSG_OWN_INTERVAL,
+                        .burst = DEFAULT_KMSG_OWN_BURST,
+                },
         };
 
         r = set_namespace(s, namespace);

src/journal/journald-server.h

@@ -16,6 +16,7 @@ typedef struct Server Server;
 #include "journald-stream.h"
 #include "list.h"
 #include "prioq.h"
+#include "ratelimit.h"
 #include "time-util.h"
 #include "varlink.h"
 
@@ -142,6 +143,7 @@ struct Server {
 
         uint64_t *kernel_seqnum;
         bool dev_kmsg_readable:1;
+        RateLimit kmsg_own_ratelimit;
 
         bool send_watchdog:1;
         bool sent_notify_ready:1;

test/units/testsuite-12.sh

@@ -3,6 +3,8 @@
 set -eux
 set -o pipefail
 
+echo "g adm - - -" | systemd-sysusers -
+
 U=/run/systemd/system/test12.socket
 cat >$U <<EOF
 [Unit]

test/units/testsuite-46.sh

@@ -19,7 +19,8 @@ inspect() {
     homectl inspect "$USERNAME" | tee /tmp/a
     userdbctl user "$USERNAME" | tee /tmp/b
 
-    diff -I '/^\s*Disk (Size|Free|Floor|Ceiling):/' /tmp/{a,b}
+    # diff uses the grep BREs for pattern matching
+    diff -I '^\s*Disk \(Size\|Free\|Floor\|Ceiling\):' /tmp/{a,b}
     rm /tmp/{a,b}
 }