From 25de94a998da9a1044aa2ab382c9191335aeb1fc Mon Sep 17 00:00:00 2001
From: Natalia Portillo <claunia@claunia.com>
Date: Thu, 31 Jul 2025 15:04:38 +0100
Subject: [PATCH] [Specification] Add index block continuation (`IDXC`)

---
 docs/spec/spec.adoc                       |  6 ++-
 docs/spec/structs/index_continuation.adoc | 45 +++++++++++++++++++++++
 2 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 docs/spec/structs/index_continuation.adoc

diff --git a/docs/spec/spec.adoc b/docs/spec/spec.adoc
index 2781066..aea6a48 100644
--- a/docs/spec/spec.adoc
+++ b/docs/spec/spec.adoc
@@ -38,4 +38,8 @@ include::structs/blocks.adoc[]
 
 <<<
 
-include::structs/index2.adoc[]
\ No newline at end of file
+include::structs/index2.adoc[]
+
+<<<
+
+include::structs/index_continuation.adoc[]
\ No newline at end of file
diff --git a/docs/spec/structs/index_continuation.adoc b/docs/spec/structs/index_continuation.adoc
new file mode 100644
index 0000000..823d9f3
--- /dev/null
+++ b/docs/spec/structs/index_continuation.adoc
@@ -0,0 +1,45 @@
+=== The index block continuation (`IDXC`)
+
+The index block continuation follows the same structure and semantics as the index block version 2, with the exception that it includes a pointer to the preceding index block or index block continuation.
+
+At most, a single index block continuation may appear within any index block structure.
+
+The purpose of this block is to enable incremental indexing prior to finalizing the image file.
+This allows new blocks to be indexed as they are written, facilitating partial recovery in the event of application failure.
+
+The block is immediately followed by index entries formatted identically to those defined in index block version 2.
+
+==== Structure Definition
+
+[source,c]
+/* Undefined */
+
+==== Field Descriptions
+
+[cols="2,2,2,6",options="header"]
+|===
+|Type
+|Size
+|Name
+|Description
+
+|uint32
+|4 bytes
+|identifier
+|The index block identifier, always `IDXC`
+
+|uint64
+|8 bytes
+|entries
+|The number of entries following this header
+
+|uint64
+|8 bytes
+|crc64
+|CRC64-ECMA checksum of the entries following this header
+
+|uint64
+|8 bytes
+|previous
+|Pointer in image file to previous index block
+|===
\ No newline at end of file