Howto implement a backend - SpaceCafe/julea GitHub Wiki
Implementing an additional backend storage system is usually done in a single .c-file. At the beginning, a final decision has to been taken: is this backend connectable via JULEA client or server?
Therefore, a file should be created in backend/client/ or backend/server/.
Here is a basic template, which could be used to create an implementation:
#include <julea-config.h>
#include <glib.h>
#include <gmodule.h>
#include <julea.h>
static gboolean backend_create (gchar const* namespace, gchar const* path, gpointer* data)
{
// PREPARE STUFF
j_trace_file_begin(full_path, J_TRACE_FILE_CREATE);
// DO STUFF
j_trace_file_end(full_path, J_TRACE_FILE_CREATE, 0, 0);
// FOLLOW UP STUFF
return TRUE;
}
static gboolean backend_open (gchar const* namespace, gchar const* path, gpointer* data)
{
// PREPARE STUFF
j_trace_file_begin(full_path, J_TRACE_FILE_OPEN);
// DO STUFF
j_trace_file_end(full_path, J_TRACE_FILE_OPEN, 0, 0);
// FOLLOW UP STUFF
return TRUE;
}
static gboolean backend_delete (gpointer data)
{
// PREPARE STUFF
j_trace_file_begin(bf->path, J_TRACE_FILE_DELETE);
// DO STUFF
j_trace_file_end(bf->path, J_TRACE_FILE_DELETE, 0, 0);
// FOLLOW UP STUFF
return TRUE;
}
static gboolean backend_close (gpointer data)
{
// PREPARE STUFF
j_trace_file_begin(bf->path, J_TRACE_FILE_CLOSE);
// DO STUFF
j_trace_file_end(bf->path, J_TRACE_FILE_CLOSE, 0, 0);
// FOLLOW UP STUFF
return TRUE;
}
static gboolean backend_status (gpointer data, gint64* modification_time, guint64* size)
{
// PREPARE STUFF
j_trace_file_begin(bf->path, J_TRACE_FILE_STATUS);
// DO STUFF
j_trace_file_end(bf->path, J_TRACE_FILE_STATUS, 0, 0);
// FOLLOW UP STUFF
return TRUE;
}
static gboolean backend_sync (gpointer data)
{
// PREPARE STUFF
j_trace_file_begin(bf->path, J_TRACE_FILE_SYNC);
// DO STUFF
j_trace_file_end(bf->path, J_TRACE_FILE_SYNC, 0, 0);
// FOLLOW UP STUFF
return TRUE;
}
static gboolean backend_read (gpointer data, gpointer buffer, guint64 length, guint64 offset, guint64* bytes_read)
{
// PREPARE STUFF
j_trace_file_begin(bf->path, J_TRACE_FILE_READ);
// DO STUFF
j_trace_file_end(bf->path, J_TRACE_FILE_READ, length, offset);
// FOLLOW UP STUFF
return TRUE;
}
static gboolean backend_write (gpointer data, gconstpointer buffer, guint64 length, guint64 offset, guint64* bytes_written)
{
// PREPARE STUFF
j_trace_file_begin(bf->path, J_TRACE_FILE_WRITE);
// DO STUFF
j_trace_file_end(bf->path, J_TRACE_FILE_WRITE, length, offset);
// FOLLOW UP STUFF
return TRUE;
}
static gboolean backend_init (gchar const* path)
{
// DO STUFF
return TRUE;
}
static void backend_fini (void)
{
// DO STUFF
}
static
JBackend my_new_backend = {
.type = J_BACKEND_TYPE_OBJECT,
.object = {
.init = backend_init,
.fini = backend_fini,
.create = backend_create,
.delete = backend_delete,
.open = backend_open,
.close = backend_close,
.status = backend_status,
.sync = backend_sync,
.read = backend_read,
.write = backend_write
}
};
G_MODULE_EXPORT
JBackend*
backend_info (JBackendType type)
{
JBackend* backend = NULL;
if (type == J_BACKEND_TYPE_OBJECT)
{
backend = &my_new_backend;
}
return backend;
}
Currently, the Python-written buildsystem called Waf is been used. To add your implementation to the build chain, a little Python has to been written. The following code snippets shows, how librados is added to Waf.
At first, you want to add an optional parameter for using your new backend.
ctx.add_option('--librados', action='store', default=None, help='librados driver prefix')
The next step is defining an environment variable with its preferences, like libraries to use or its obligation.
ctx.env.JULEA_LIBRADOS = \
ctx.check_cc(
lib = 'rados',
uselib_store = 'LIBRADOS',
mandatory = False
)
At least, tell Waf weather you backend is a client or server component.
if ctx.env.JULEA_LIBRADOS:
backends_client.append('rados')
for backend in backends_client:
use_extra = []
if backend == 'mongodb':
use_extra = ['LIBMONGOC']
elif backend == 'rados':
use_extra = ['LIBRADOS']