Document the propagation functions.

src/csync_propagate.h

@@ -23,10 +23,51 @@
 
 #include <sys/types.h>
 
+/**
+ * @file csync_reconcile.h
+ *
+ * @brief Propagation
+ *
+ * It uses the calculated records to apply them on the current replica. The
+ * propagator uses a two-phase-commit mechanism to simulate an atomic
+ * filesystem operation.
+ *
+ * In the first phase we copy the file to a temporary file on the opposite
+ * replica. This has the advantage that we can check if file which has been
+ * copied to the opposite replica has been transfered successfully. If the
+ * connection gets interrupted during the transfer we still have the original
+ * states of the file. This means no data will be lost.
+ *
+ * In the second phase the file on the opposite replica will be overwritten by
+ * the temporary file.
+ *
+ * After a successful propagation we have to merge the trees to reflect the
+ * current state of the filesystem tree. This updated tree will be written as a
+ * journal into the state database. It will be used during the update detection
+ * of the next synchronization. See above for a description of the state
+ * database during synchronization.
+ *
+ * @defgroup csyncPropagationInternals csync propagation internals
+ * @ingroup csyncInternalAPI
+ *
+ * @{
+ */
+
 #define C_FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
 #define C_DIR_MODE (S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH)
 
+/**
+ * @brief Propagate all files.
+ *
+ * @param  ctx          The csync context to use for propagation.
+ *
+ * @return 0 on success, < 0 on error.
+ */
 int csync_propagate_files(CSYNC *ctx);
 
+/**
+ * }@
+ */
 #endif /* _CSYNC_PROPAGATE_H */
+
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