journald: rework --sync/--rotate logic to use CLOCK_MONOTONIC timestamp files

Previously, we'd rely on the mtime timestamps of the touch files to see
if our sync/rotation requests were already suppressed. This means we
rely on CLOCK_REALTIME timestamps. With this patch we instead store the
CLOCK_MONOTONIC timestamp *in* the touch files, and avoid relying on
mtime.

This should make things more reliable when the clock or underlying mtime
granularity is not very good.

This also adds warning messages if writing any of the flag files fails.

4 files changed, 61 insertions, 13 deletions

diff --git a/src/basic/fileio.c b/src/basic/fileio.c
index 619dafb517..be6e327690 100644
--- a/src/basic/fileio.c
+++ b/src/basic/fileio.c
@@ -28,8 +28,10 @@
 #include "fileio.h"
 #include "fs-util.h"
 #include "hexdecoct.h"
+#include "parse-util.h"
 #include "path-util.h"
 #include "random-util.h"
+#include "stdio-util.h"
 #include "string-util.h"
 #include "strv.h"
 #include "umask-util.h"
@@ -1149,3 +1151,37 @@ int tempfn_random_child(const char *p, const char *extra, char **ret) {
         *ret = path_kill_slashes(t);
         return 0;
 }
+
+int write_timestamp_file_atomic(const char *fn, usec_t n) {
+        char ln[DECIMAL_STR_MAX(n)+2];
+
+        /* Creates a "timestamp" file, that contains nothing but a
+         * usec_t timestamp, formatted in ASCII. */
+
+        if (n <= 0 || n >= USEC_INFINITY)
+                return -ERANGE;
+
+        xsprintf(ln, USEC_FMT "\n", n);
+
+        return write_string_file(fn, ln, WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_ATOMIC);
+}
+
+int read_timestamp_file(const char *fn, usec_t *ret) {
+        _cleanup_free_ char *ln = NULL;
+        uint64_t t;
+        int r;
+
+        r = read_one_line_file(fn, &ln);
+        if (r < 0)
+                return r;
+
+        r = safe_atou64(ln, &t);
+        if (r < 0)
+                return r;
+
+        if (t <= 0 || t >= (uint64_t) USEC_INFINITY)
+                return -ERANGE;
+
+        *ret = (usec_t) t;
+        return 0;
+}
diff --git a/src/basic/fileio.h b/src/basic/fileio.h
index fa7f192331..5f2c941498 100644
--- a/src/basic/fileio.h
+++ b/src/basic/fileio.h
@@ -28,6 +28,7 @@
 #include <sys/types.h>
 
 #include "macro.h"
+#include "time-util.h"
 
 typedef enum {
         WRITE_STRING_FILE_CREATE = 1,
@@ -77,3 +78,6 @@ int open_tmpfile(const char *path, int flags);
 int tempfn_xxxxxx(const char *p, const char *extra, char **ret);
 int tempfn_random(const char *p, const char *extra, char **ret);
 int tempfn_random_child(const char *p, const char *extra, char **ret);
+
+int write_timestamp_file_atomic(const char *fn, usec_t n);
+int read_timestamp_file(const char *fn, usec_t *ret);
diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index ac0751c547..75a48c761c 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -1838,7 +1838,7 @@ static int send_signal_and_wait(int sig, const char *watch_path) {
                 return -EOPNOTSUPP;
         }
 
-        start = now(CLOCK_REALTIME);
+        start = now(CLOCK_MONOTONIC);
 
         /* This call sends the specified signal to journald, and waits
          * for acknowledgment by watching the mtime of the specified
@@ -1846,16 +1846,14 @@ static int send_signal_and_wait(int sig, const char *watch_path) {
          * then wait for the operation to complete. */
 
         for (;;) {
-                struct stat st;
+                usec_t tstamp;
 
                 /* See if a sync happened by now. */
-                if (stat(watch_path, &st) < 0) {
-                        if (errno != ENOENT)
-                                return log_error_errno(errno, "Failed to stat %s: %m", watch_path);
-                } else {
-                        if (timespec_load(&st.st_mtim) >= start)
-                                return 0;
-                }
+                r = read_timestamp_file(watch_path, &tstamp);
+                if (r < 0 && r != -ENOENT)
+                        return log_error_errno(errno, "Failed to read %s: %m", watch_path);
+                if (r >= 0 && tstamp >= start)
+                        return 0;
 
                 /* Let's ask for a sync, but only once. */
                 if (!bus) {
@@ -1889,7 +1887,7 @@ static int send_signal_and_wait(int sig, const char *watch_path) {
                         if (watch_fd < 0)
                                 return log_error_errno(errno, "Failed to create inotify watch: %m");
 
-                        r = inotify_add_watch(watch_fd, "/run/systemd/journal", IN_CREATE|IN_ATTRIB|IN_DONT_FOLLOW|IN_ONLYDIR);
+                        r = inotify_add_watch(watch_fd, "/run/systemd/journal", IN_MOVED_TO|IN_DONT_FOLLOW|IN_ONLYDIR);
                         if (r < 0)
                                 return log_error_errno(errno, "Failed to watch journal directory: %m");
 
diff --git a/src/journal/journald-server.c b/src/journal/journald-server.c
index 70ff101d5f..762b810109 100644
--- a/src/journal/journald-server.c
+++ b/src/journal/journald-server.c
@@ -41,6 +41,7 @@
 #include "dirent-util.h"
 #include "extract-word.h"
 #include "fd-util.h"
+#include "fileio.h"
 #include "formats-util.h"
 #include "fs-util.h"
 #include "hashmap.h"
@@ -1240,6 +1241,7 @@ int server_process_datagram(sd_event_source *es, int fd, uint32_t revents, void
 
 static int dispatch_sigusr1(sd_event_source *es, const struct signalfd_siginfo *si, void *userdata) {
         Server *s = userdata;
+        int r;
 
         assert(s);
 
@@ -1249,13 +1251,16 @@ static int dispatch_sigusr1(sd_event_source *es, const struct signalfd_siginfo *
         server_sync(s);
         server_vacuum(s, false, false);
 
-        (void) touch("/run/systemd/journal/flushed");
+        r = touch("/run/systemd/journal/flushed");
+        if (r < 0)
+                log_warning_errno(r, "Failed to touch /run/systemd/journal/flushed, ignoring: %m");
 
         return 0;
 }
 
 static int dispatch_sigusr2(sd_event_source *es, const struct signalfd_siginfo *si, void *userdata) {
         Server *s = userdata;
+        int r;
 
         assert(s);
 
@@ -1264,7 +1269,9 @@ static int dispatch_sigusr2(sd_event_source *es, const struct signalfd_siginfo *
         server_vacuum(s, true, true);
 
         /* Let clients know when the most recent rotation happened. */
-        (void) touch("/run/systemd/journal/rotated");
+        r = write_timestamp_file_atomic("/run/systemd/journal/rotated", now(CLOCK_MONOTONIC));
+        if (r < 0)
+                log_warning_errno(r, "Failed to write /run/systemd/journal/rotated, ignoring: %m");
 
         return 0;
 }
@@ -1282,6 +1289,7 @@ static int dispatch_sigterm(sd_event_source *es, const struct signalfd_siginfo *
 
 static int dispatch_sigrtmin1(sd_event_source *es, const struct signalfd_siginfo *si, void *userdata) {
         Server *s = userdata;
+        int r;
 
         assert(s);
 
@@ -1290,7 +1298,9 @@ static int dispatch_sigrtmin1(sd_event_source *es, const struct signalfd_siginfo
         server_sync(s);
 
         /* Let clients know when the most recent sync happened. */
-        (void) touch("/run/systemd/journal/synced");
+        r = write_timestamp_file_atomic("/run/systemd/journal/synced", now(CLOCK_MONOTONIC));
+        if (r < 0)
+                log_warning_errno(r, "Failed to write /run/systemd/journal/synced, ignoring: %m");
 
         return 0;
 }