sd-journal: "soft" deprecate sd_journal_open_container()

Let's document the call as deprecated, since it doesn't cover containers with
directories that aren#t visible to the host properly.

src/journal/sd-journal.c

@@ -1767,6 +1767,9 @@ _public_ int sd_journal_open_container(sd_journal **ret, const char *machine, in
         char *p;
         int r;
 
+        /* This is pretty much deprecated, people should use machined's OpenMachineRootDirectory() call instead in
+         * combination with sd_journal_open_directory_fd(). */
+
         assert_return(machine, -EINVAL);
         assert_return(ret, -EINVAL);
         assert_return((flags & ~(SD_JOURNAL_LOCAL_ONLY|SD_JOURNAL_SYSTEM)) == 0, -EINVAL);

src/systemd/sd-journal.h

@@ -88,7 +88,7 @@ int sd_journal_open_directory(sd_journal **ret, const char *path, int flags);
 int sd_journal_open_directory_fd(sd_journal **ret, int fd, int flags);
 int sd_journal_open_files(sd_journal **ret, const char **paths, int flags);
 int sd_journal_open_files_fd(sd_journal **ret, int fds[], unsigned n_fds, int flags);
-int sd_journal_open_container(sd_journal **ret, const char *machine, int flags);
+int sd_journal_open_container(sd_journal **ret, const char *machine, int flags); /* deprecated */
 void sd_journal_close(sd_journal *j);
 
 int sd_journal_previous(sd_journal *j);