reader: add SD_JOURNAL_OS_ROOT and rework flag passing

Let's pass any flags through to the journal functions without checking
validity. Those functions do their own checking, so there's no need to
second-guess.

The semantics for _Reader(flags=0) are a bit changed:
before, this would be transformed into sd_journal_open(SD_J_LOCAL_ONLY).
Now, this results in sd_journal_open(0). Previous behaviour should be
achieved by not specifying the flags at all.
This change is necessary, because previously it was not possible to
pass flags=0 to sd_journal_open(0), i.e. it was not possible to "merge"
journals through the Python interface.

Similarly, Reader(flags=0) now means to open all journals, and
Reader(flags=None) is the same as Reader(flags=LOCAL_ONLY).

4 files changed, 51 insertions, 24 deletions

diff --git a/docs/journal.rst b/docs/journal.rst
index 8e4b5b6..49c07b1 100644
--- a/docs/journal.rst
+++ b/docs/journal.rst
@@ -89,6 +89,7 @@ Journal access types
 .. autoattribute:: systemd.journal.RUNTIME_ONLY
 .. autoattribute:: systemd.journal.SYSTEM
 .. autoattribute:: systemd.journal.CURRENT_USER
+.. autoattribute:: systemd.journal.OS_ROOT
 
 Journal event types
 ~~~~~~~~~~~~~~~~~~~
diff --git a/systemd/_reader.c b/systemd/_reader.c
index 020bfbd..0f6fd3f 100644
--- a/systemd/_reader.c
+++ b/systemd/_reader.c
@@ -34,8 +34,8 @@
 #if defined(LIBSYSTEMD_VERSION) || LIBSYSTEMD_JOURNAL_VERSION > 204
 #  define HAVE_JOURNAL_OPEN_FILES
 #else
-#  define SD_JOURNAL_SYSTEM 4
-#  define SD_JOURNAL_CURRENT_USER 8
+#  define SD_JOURNAL_SYSTEM        (1 << 2)
+#  define SD_JOURNAL_CURRENT_USER  (1 << 3)
 #endif
 
 #if LIBSYSTEMD_VERSION >= 229
@@ -46,6 +46,8 @@
 
 #if LIBSYSTEMD_VERSION >= 230
 #  define HAVE_JOURNAL_OPEN_DIRECTORY_FD
+#else
+#  define SD_JOURNAL_OS_ROOT       (1 << 4)
 #endif
 
 typedef struct {
@@ -225,7 +227,9 @@ PyDoc_STRVAR(Reader__doc__,
              "Argument `flags` sets open flags of the journal, which can be one of, or an ORed\n"
              "combination of constants: LOCAL_ONLY (default) opens journal on local machine only;\n"
              "RUNTIME_ONLY opens only volatile journal files; and SYSTEM opens journal files of\n"
-             "system services and the kernel, and CURRENT_USER opens file of the current user.\n"
+             "system services and the kernel, CURRENT_USER opens files of the current user; and\n"
+             "OS_ROOT is used to open the journal from directories relative to the specified\n"
+             "directory path or file descriptor.\n"
              "\n"
              "Instead of opening the system journal, argument `path` may specify a directory\n"
              "which contains the journal. It maybe be either a file system path (a string), or\n"
@@ -235,8 +239,9 @@ PyDoc_STRVAR(Reader__doc__,
              "_Reader implements the context manager protocol: the journal will be closed when\n"
              "exiting the block.");
 static int Reader_init(Reader *self, PyObject *args, PyObject *keywds) {
-        int flags = 0, r;
+        unsigned flags = SD_JOURNAL_LOCAL_ONLY;
         PyObject *_path = NULL, *_files = NULL;
+        int r;
 
         static const char* const kwlist[] = {"flags", "path", "files", NULL};
         if (!PyArg_ParseTupleAndKeywords(args, keywds, "|iO&O&:__init__", (char**) kwlist,
@@ -245,9 +250,9 @@ static int Reader_init(Reader *self, PyObject *args, PyObject *keywds) {
                                          null_converter, &_files))
                 return -1;
 
-        if (!!flags + !!_path + !!_files > 1) {
+        if (!!_path + !!_files > 1) {
                 PyErr_SetString(PyExc_ValueError,
-                                "cannot use more than one of flags, path, and files");
+                                "path and files cannot be specified simultaneously");
                 return -1;
         }
 
@@ -260,7 +265,7 @@ static int Reader_init(Reader *self, PyObject *args, PyObject *keywds) {
 
 #ifdef HAVE_JOURNAL_OPEN_DIRECTORY_FD
                         Py_BEGIN_ALLOW_THREADS
-                        r = sd_journal_open_directory_fd(&self->j, (int) fd, 0);
+                        r = sd_journal_open_directory_fd(&self->j, (int) fd, flags);
                         Py_END_ALLOW_THREADS
 #else
                         r = -ENOSYS;
@@ -274,7 +279,7 @@ static int Reader_init(Reader *self, PyObject *args, PyObject *keywds) {
                                 return -1;
 
                         Py_BEGIN_ALLOW_THREADS
-                        r = sd_journal_open_directory(&self->j, path, 0);
+                        r = sd_journal_open_directory(&self->j, path, flags);
                         Py_END_ALLOW_THREADS
                 }
         } else if (_files) {
@@ -289,7 +294,7 @@ static int Reader_init(Reader *self, PyObject *args, PyObject *keywds) {
                                 return -1;
 
                         Py_BEGIN_ALLOW_THREADS
-                        r = sd_journal_open_files(&self->j, (const char**) files, 0);
+                        r = sd_journal_open_files(&self->j, (const char**) files, flags);
                         Py_END_ALLOW_THREADS
                 } else {
                         _cleanup_free_ int *fds = NULL;
@@ -299,16 +304,13 @@ static int Reader_init(Reader *self, PyObject *args, PyObject *keywds) {
                                 return -1;
 
                         Py_BEGIN_ALLOW_THREADS
-                        r = sd_journal_open_files_fd(&self->j, fds, n_fds, 0);
+                        r = sd_journal_open_files_fd(&self->j, fds, n_fds, flags);
                         Py_END_ALLOW_THREADS
                 }
 #else
                 r = -ENOSYS;
 #endif
         } else {
-                if (!flags)
-                        flags = SD_JOURNAL_LOCAL_ONLY;
-
                 Py_BEGIN_ALLOW_THREADS
                 r = sd_journal_open(&self->j, flags);
                 Py_END_ALLOW_THREADS
@@ -1332,6 +1334,7 @@ init_reader(void)
             PyModule_AddIntConstant(m, "SYSTEM", SD_JOURNAL_SYSTEM) ||
             PyModule_AddIntConstant(m, "SYSTEM_ONLY", SD_JOURNAL_SYSTEM_ONLY) ||
             PyModule_AddIntConstant(m, "CURRENT_USER", SD_JOURNAL_CURRENT_USER) ||
+            PyModule_AddIntConstant(m, "OS_ROOT", SD_JOURNAL_OS_ROOT) ||
             PyModule_AddStringConstant(m, "__version__", PACKAGE_VERSION)) {
 #if PY_MAJOR_VERSION >= 3
                 Py_DECREF(m);
diff --git a/systemd/journal.py b/systemd/journal.py
index 4440dec..b91337d 100644
--- a/systemd/journal.py
+++ b/systemd/journal.py
@@ -34,6 +34,7 @@ from ._journal import __version__, sendv, stream_fd
 from ._reader import (_Reader, NOP, APPEND, INVALIDATE,
                       LOCAL_ONLY, RUNTIME_ONLY,
                       SYSTEM, SYSTEM_ONLY, CURRENT_USER,
+                      OS_ROOT,
                       _get_catalog)
 from . import id128 as _id128
 
@@ -131,7 +132,7 @@ class Reader(_Reader):
     journal.
 
     """
-    def __init__(self, flags=0, path=None, files=None, converters=None):
+    def __init__(self, flags=None, path=None, files=None, converters=None):
         """Create a new Reader.
 
         Argument `flags` defines the open flags of the journal, which can be one
@@ -155,6 +156,13 @@ class Reader(_Reader):
         Reader implements the context manager protocol: the journal will be
         closed when exiting the block.
         """
+        if flags is None:
+            if path is None and files is None:
+                # This mimics journalctl behaviour of default to local journal only
+                flags = LOCAL_ONLY
+            else:
+                flags = 0
+
         super(Reader, self).__init__(flags, path, files)
         if _sys.version_info >= (3,3):
             self.converters = _ChainMap()
diff --git a/systemd/test/test_journal.py b/systemd/test/test_journal.py
index 4b23a70..10a57e9 100644
--- a/systemd/test/test_journal.py
+++ b/systemd/test/test_journal.py
@@ -43,15 +43,25 @@ def test_reader_init_flags():
     j2 = journal.Reader(journal.LOCAL_ONLY)
     j3 = journal.Reader(journal.RUNTIME_ONLY)
     j4 = journal.Reader(journal.SYSTEM_ONLY)
-    j5 = journal.Reader(journal.LOCAL_ONLY|
-                        journal.RUNTIME_ONLY|
-                        journal.SYSTEM_ONLY)
+    j5 = journal.Reader(journal.LOCAL_ONLY | journal.RUNTIME_ONLY | journal.SYSTEM_ONLY)
     j6 = journal.Reader(0)
 
-def test_reader_init_path(tmpdir):
-    j = journal.Reader(path=tmpdir.strpath)
+def test_reader_os_root(tmpdir):
     with pytest.raises(ValueError):
-        journal.Reader(journal.LOCAL_ONLY, path=tmpdir.strpath)
+        journal.Reader(journal.OS_ROOT)
+    j1 = journal.Reader(path=tmpdir.strpath,
+                        flags=journal.OS_ROOT)
+    j2 = journal.Reader(path=tmpdir.strpath,
+                        flags=journal.OS_ROOT | journal.CURRENT_USER)
+    j3 = journal.Reader(path=tmpdir.strpath,
+                        flags=journal.OS_ROOT | journal.SYSTEM_ONLY)
+
+def test_reader_init_path(tmpdir):
+    j1 = journal.Reader(path=tmpdir.strpath)
+    journal.Reader(0, path=tmpdir.strpath)
+
+    j2 = journal.Reader(path=tmpdir.strpath)
+    journal.Reader(path=tmpdir.strpath)
 
 def test_reader_init_path_invalid_fd():
     with pytest.raises(OSError):
@@ -63,10 +73,15 @@ def test_reader_init_path_nondirectory_fd():
 
 def test_reader_init_path_fd(tmpdir):
     fd = os.open(tmpdir.strpath, os.O_RDONLY)
-    j = journal.Reader(path=fd)
-    with pytest.raises(ValueError):
-        journal.Reader(journal.LOCAL_ONLY, path=fd)
-    assert list(j) == []
+
+    j1 = journal.Reader(path=fd)
+    assert list(j1) == []
+
+    j2 = journal.Reader(journal.SYSTEM, path=fd)
+    assert list(j2) == []
+
+    j3 = journal.Reader(journal.CURRENT_USER, path=fd)
+    assert list(j3) == []
 
 def test_reader_as_cm(tmpdir):
     j = journal.Reader(path=tmpdir.strpath)