Signed-off-by: Thomas Schoebel-Theuer <[email protected]>
---
include/linux/brick/meta.h | 90 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 90 insertions(+)
create mode 100644 include/linux/brick/meta.h
diff --git a/include/linux/brick/meta.h b/include/linux/brick/meta.h
new file mode 100644
index 0000000..44104fd
--- /dev/null
+++ b/include/linux/brick/meta.h
@@ -0,0 +1,90 @@
+/* (c) 2010 Thomas Schoebel-Theuer / 1&1 Internet AG */
+#ifndef META_H
+#define META_H
+
+/***********************************************************************/
+
+/* metadata descriptions */
+
+/* The idea is to describe your C structures in such a way that
+ * transfers to disk or over a network become self-describing.
+ *
+ * In essence, this is a kind of version-independent marshalling.
+ *
+ * Advantage:
+ * When you extend your original C struct (and of course update the
+ * corresponding meta structure), old data on disk (or network peers
+ * running an old version of your program) will remain valid.
+ * Upon read, newly added fields missing in the old version will be simply
+ * not filled in and therefore remain zeroed (if you don't forget to
+ * initially clear your structures via memset() / initializers / etc).
+ * Note that this works only if you never rename or remove existing
+ * fields; you should only add new ones.
+ * [TODO: add macros for description of ignored / renamed fields to
+ * overcome this limitation]
+ * You may increase the size of integers, for example from 32bit to 64bit
+ * or even higher; sign extension will be automatically carried out
+ * when necessary.
+ * Also, you may change the order of fields, because the metadata interpreter
+ * will check each field individually; field offsets are automatically
+ * maintained.
+ *
+ * Disadvantage: this adds some (small) overhead.
+ */
+
+enum field_type {
+ FIELD_DONE,
+ FIELD_REF,
+ FIELD_SUB,
+ FIELD_STRING,
+ FIELD_RAW,
+ FIELD_INT,
+ FIELD_UINT,
+};
+
+struct meta {
+ /* char field_name[MAX_FIELD_LEN]; */
+ char *field_name;
+
+ short field_type;
+ short field_data_size;
+ short field_transfer_size;
+ int field_offset;
+ const struct meta *field_ref;
+};
+
+#define _META_INI(NAME, STRUCT, TYPE, TSIZE) \
+ .field_name = #NAME, \
+ .field_type = TYPE, \
+ .field_data_size = sizeof(((STRUCT *)NULL)->NAME), \
+ .field_transfer_size = (TSIZE), \
+ .field_offset = offsetof(STRUCT, NAME) \
+
+#define META_INI_TRANSFER(NAME, STRUCT, TYPE, TSIZE) \
+ { _META_INI(NAME, STRUCT, TYPE, TSIZE) }
+
+#define META_INI(NAME, STRUCT, TYPE) \
+ { _META_INI(NAME, STRUCT, TYPE, 0) }
+
+#define _META_INI_AIO(NAME, STRUCT, AIO) \
+ .field_name = #NAME, \
+ .field_type = FIELD_REF, \
+ .field_data_size = sizeof(*(((STRUCT *)NULL)->NAME)), \
+ .field_offset = offsetof(STRUCT, NAME), \
+ .field_ref = AIO
+
+#define META_INI_AIO(NAME, STRUCT, AIO) { _META_INI_AIO(NAME, STRUCT, AIO) }
+
+#define _META_INI_SUB(NAME, STRUCT, SUB) \
+ .field_name = #NAME, \
+ .field_type = FIELD_SUB, \
+ .field_data_size = sizeof(((STRUCT *)NULL)->NAME), \
+ .field_offset = offsetof(STRUCT, NAME), \
+ .field_ref = SUB
+
+#define META_INI_SUB(NAME, STRUCT, SUB) { _META_INI_SUB(NAME, STRUCT, SUB) }
+
+extern const struct meta *find_meta(const struct meta *meta, const char
*field_name);
+/* extern void free_meta(void *data, const struct meta *meta); */
+
+#endif
--
2.0.0
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