journal: provide an API that allows client to figure out whether they need to recheck the journal manually for changes in regular intervals

Network file systems generally do not offer inotify() that would work
across the network. We hence cannot rely on inotify() exclusiely in
those case. Provide an API to determine these cases, and suggest doing
manual regular rechecks.

Note that this is not complete yet, as we need to rescan journal dirs on
network file systems explicitly to find new/removed files

5 files changed, 57 insertions, 0 deletions

diff --git a/src/journal/journal-internal.h b/src/journal/journal-internal.h
index f68ca996a8..75a4129e5b 100644
--- a/src/journal/journal-internal.h
+++ b/src/journal/journal-internal.h
@@ -119,6 +119,8 @@ struct sd_journal {
         char *unique_field;
         JournalFile *unique_file;
         uint64_t unique_offset;
+
+        bool on_network;
 };
 
 char *journal_make_match_string(sd_journal *j);
diff --git a/src/journal/libsystemd-journal.sym b/src/journal/libsystemd-journal.sym
index 96293b8a29..ad78fcc74d 100644
--- a/src/journal/libsystemd-journal.sym
+++ b/src/journal/libsystemd-journal.sym
@@ -80,3 +80,8 @@ global:
         sd_journal_enumerate_unique;
         sd_journal_restart_unique;
 } LIBSYSTEMD_JOURNAL_190;
+
+LIBSYSTEMD_JOURNAL_196 {
+global:
+        sd_journal_fd_reliable;
+} LIBSYSTEMD_JOURNAL_195;
diff --git a/src/journal/sd-journal.c b/src/journal/sd-journal.c
index d5d2d78f1c..a346691e21 100644
--- a/src/journal/sd-journal.c
+++ b/src/journal/sd-journal.c
@@ -25,6 +25,8 @@
 #include <unistd.h>
 #include <sys/inotify.h>
 #include <sys/poll.h>
+#include <sys/vfs.h>
+#include <linux/magic.h>
 
 #include "sd-journal.h"
 #include "journal-def.h"
@@ -35,9 +37,12 @@
 #include "lookup3.h"
 #include "compress.h"
 #include "journal-internal.h"
+#include "missing.h"
 
 #define JOURNAL_FILES_MAX 1024
 
+#define JOURNAL_FILES_RECHECK_USEC (2 * USEC_PER_SEC)
+
 static void detach_location(sd_journal *j) {
         Iterator i;
         JournalFile *f;
@@ -1184,6 +1189,25 @@ _public_ int sd_journal_seek_tail(sd_journal *j) {
         return 0;
 }
 
+static void check_network(sd_journal *j, int fd) {
+        struct statfs sfs;
+
+        assert(j);
+
+        if (j->on_network)
+                return;
+
+        if (fstatfs(fd, &sfs) < 0)
+                return;
+
+        j->on_network =
+                sfs.f_type == CIFS_MAGIC_NUMBER ||
+                sfs.f_type == CODA_SUPER_MAGIC ||
+                sfs.f_type == NCP_SUPER_MAGIC ||
+                sfs.f_type == NFS_SUPER_MAGIC ||
+                sfs.f_type == SMB_SUPER_MAGIC;
+}
+
 static int add_file(sd_journal *j, const char *prefix, const char *filename) {
         char *path;
         int r;
@@ -1233,6 +1257,8 @@ static int add_file(sd_journal *j, const char *prefix, const char *filename) {
                 return r;
         }
 
+        check_network(j, f->fd);
+
         j->current_invalidate_counter ++;
 
         log_debug("File %s got added.", f->path);
@@ -1366,6 +1392,8 @@ static int add_directory(sd_journal *j, const char *prefix, const char *dirname)
                 }
         }
 
+        check_network(j, dirfd(d));
+
         closedir(d);
 
         return 0;
@@ -1453,6 +1481,8 @@ static int add_root_directory(sd_journal *j, const char *p) {
                 }
         }
 
+        check_network(j, dirfd(d));
+
         closedir(d);
 
         return 0;
@@ -2079,6 +2109,14 @@ _public_ int sd_journal_wait(sd_journal *j, uint64_t timeout_usec) {
                 return determine_change(j);
         }
 
+        if (j->on_network) {
+                /* If we are on the network we need to regularly check
+                 * for changes manually */
+
+                if (timeout_usec == (uint64_t) -1 || timeout_usec > JOURNAL_FILES_RECHECK_USEC)
+                        timeout_usec = JOURNAL_FILES_RECHECK_USEC;
+        }
+
         do {
                 r = fd_wait_for_event(j->inotify_fd, POLLIN, timeout_usec);
         } while (r == -EINTR);
@@ -2344,3 +2382,10 @@ _public_ void sd_journal_restart_unique(sd_journal *j) {
         j->unique_file = NULL;
         j->unique_offset = 0;
 }
+
+_public_ int sd_journal_reliable_fd(sd_journal *j) {
+        if (!j)
+                return -EINVAL;
+
+        return !j->on_network;
+}
diff --git a/src/shared/missing.h b/src/shared/missing.h
index f58a609c7d..3777cf69b2 100644
--- a/src/shared/missing.h
+++ b/src/shared/missing.h
@@ -249,3 +249,7 @@ static inline int name_to_handle_at(int fd, const char *name, struct file_handle
 #    error neither secure_getenv nor __secure_getenv are available
 #  endif
 #endif
+
+#ifndef CIFS_MAGIC_NUMBER
+#define CIFS_MAGIC_NUMBER 0xFF534D42
+#endif
diff --git a/src/systemd/sd-journal.h b/src/systemd/sd-journal.h
index 55281b1346..7241173035 100644
--- a/src/systemd/sd-journal.h
+++ b/src/systemd/sd-journal.h
@@ -124,6 +124,7 @@ int sd_journal_enumerate_unique(sd_journal *j, const void **data, size_t *l);
 void sd_journal_restart_unique(sd_journal *j);
 
 int sd_journal_get_fd(sd_journal *j);
+int sd_journal_reliable_fd(sd_journal *j);
 int sd_journal_process(sd_journal *j);
 int sd_journal_wait(sd_journal *j, uint64_t timeout_usec);