Draft of wal.c/.h

src/wal.c

@@ -0,0 +1,99 @@
+#include "wal.h"
+#include "file_tree.h"
+
+#define WAL_MAGIC   0xcafebebe
+#define WAL_VERSION 1
+
+typedef struct {
+    uint32_t magic;
+    uint32_t version;
+    uint64_t reserved;
+} WALHeader
+
+typedef struct {
+} WALEntry;
+
+typedef struct {
+} WriteSnapshotContext;
+
+static int
+serialize_callback(char *src, int num, void *data)
+{
+    WriteSnapshotContext *wsc = data;
+    if (write(src, num) < 0)
+        return -1;
+    return 0;
+}
+
+static int write_snapshot(FileTree *file_tree)
+{
+    WriteSnapshotContext wsc;
+    if (file_tree_serialize(file_tree, serialize_callback, &wsc) < 0)
+        return -1;
+    return 0;
+}
+
+typedef struct {
+} ReadSnapshotContext;
+
+static int
+serialize_callback(char *src, int num, void *data)
+{
+    ReadSnapshotContext *rsc = data;
+    // TODO
+}
+
+static int read_snapshot(FileTree *file_tree)
+{
+    ReadSnapshotContext rsc;
+    int num = file_tree_deserialize(file_tree, deserialize_callback, &rsc);
+    if (num < 0)
+        return 0;
+    return 0;
+}
+
+static int swap_file(WAL *wal)
+{
+    // TODO:
+    //   - Create a new temporary file
+    //   - Write the WAL file header
+    //   - Serialize the current file tree
+    //   - Rename the temporary file to a name such that it's the next log file that will be used
+    //   - Delete the old log file
+    //   NOTE:
+    //     - The lock will need to be acquired at some point
+
+    assert(0); // TODO
+}
+
+int wal_open(WAL *wal, FileTree *file_tree, string file_path)
+{
+    // TODO:
+    //   - Open the log file at path "file_path"
+    //   - Lock the file
+    //   - Check that the header is correct
+    //   - Load the snapshot at the head of the file in the "file_tree" object
+    //   - Loop over the following log entries and replay them
+    //   - Then, if there are too many log entries, create a new log file and start using it
+
+    assert(0); // TODO
+}
+
+void wal_close(WAL *wal)
+{
+    // TODO:
+    //   - Unlock the file
+    //   - Close the file handle
+
+    assert(0); // TODO
+}
+
+int wal_append(WAL *wal, WALEntry entry)
+{
+    // TODO:
+    //   - If too many entries were created, start a new log file
+    //   - Write the entry
+    //   - Sync to disk
+
+    assert(0); // TODO
+}

src/wal.h

@@ -0,0 +1,11 @@
+#ifndef WAL_INCLUDED
+#define WAL_INCLUDED
+
+typedef struct {
+} WAL;
+
+int  wal_open   (WAL *wal, FileTree *file_tree, string file_path)
+void wal_close  (WAL *wal);
+int  wal_append (WAL *wal, WALEntry entry);
+
+#endif // WAL_INCLUDED