From cacaa2aadee5aabcf09bcddc942f68ad70d7c94d Mon Sep 17 00:00:00 2001
From: Afloat <132809511+Afloat16@users.noreply.github.com>
Date: Wed, 4 Nov 2026 01:12:03 +0700
Subject: [PATCH] Preserve sparse ext positions across indirect levels (from
 #705)

---
 crates/formats/src/fsread/extfs.rs          |  2 +
 crates/formats/tests/ext_sparse_indirect.rs | 41 +++++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 crates/formats/tests/ext_sparse_indirect.rs

diff --git a/crates/formats/src/fsread/extfs.rs b/crates/formats/src/fsread/extfs.rs
index 429b88e9..76fd5531 100644
--- a/crates/formats/src/fsread/extfs.rs
+++ b/crates/formats/src/fsread/extfs.rs
@@ -107,6 +107,8 @@ fn file_block_map(data: &[u8], sb: &Sb, inode_off: u64, flags: u32, nblocks: u64
         if let Some(ind) = r.u32_le(ib + 48).filter(|&p| p != 0) {
             read_indirect(data, sb, u64::from(ind), 1, per, &mut logical, &mut map);
         }
+        // The single-indirect span still occupies its logical blocks when its root is absent.
+        logical = 12 + per;
         // Double indirect.
         if let Some(dind) = r.u32_le(ib + 52).filter(|&p| p != 0) {
             read_indirect(data, sb, u64::from(dind), 2, per, &mut logical, &mut map);
diff --git a/crates/formats/tests/ext_sparse_indirect.rs b/crates/formats/tests/ext_sparse_indirect.rs
new file mode 100644
index 00000000..81e0ab80
--- /dev/null
+++ b/crates/formats/tests/ext_sparse_indirect.rs
@@ -0,0 +1,41 @@
+use craft_anything_formats::fsread::{self, Limits};
+
+const BS: usize = 1024;
+const FILE_INODE: usize = 5120 + 10 * 128;
+
+fn put(data: &mut [u8], at: usize, value: u32) {
+    data[at..at + 4].copy_from_slice(&value.to_le_bytes());
+}
+
+#[test]
+fn a_missing_single_indirect_root_keeps_the_whole_sparse_span() {
+    let mut data = craft_anything_testkit::firmware::ext_image(false);
+    data.resize(14 * BS, 0);
+    put(&mut data, 1024 + 4, 14);
+    data[FILE_INODE + 40..FILE_INODE + 100].fill(0);
+    put(&mut data, FILE_INODE + 4, (269 * BS) as u32);
+    put(&mut data, FILE_INODE + 92, 11);
+    put(&mut data, 11 * BS, 12);
+    put(&mut data, 12 * BS, 13);
+    data[13 * BS..13 * BS + 4].copy_from_slice(b"tail");
+    let image = fsread::extfs::read(&data, &Limits::default());
+    let recovered = image.entries.iter().find(|e| e.path == "hello.txt").unwrap().data.as_ref().unwrap();
+    assert!(recovered[..268 * BS].iter().all(|b| *b == 0));
+    assert_eq!(&recovered[268 * BS..268 * BS + 4], b"tail");
+    assert!(image.complete, "{:?}", image.warnings);
+}
+
+#[test]
+fn an_existing_single_indirect_block_keeps_its_original_position() {
+    let mut data = craft_anything_testkit::firmware::ext_image(false);
+    data.resize(12 * BS, 0);
+    put(&mut data, 1024 + 4, 12);
+    data[FILE_INODE + 40..FILE_INODE + 100].fill(0);
+    put(&mut data, FILE_INODE + 4, (13 * BS) as u32);
+    put(&mut data, FILE_INODE + 88, 11);
+    put(&mut data, 11 * BS, 8);
+    let image = fsread::extfs::read(&data, &Limits::default());
+    let recovered = image.entries.iter().find(|e| e.path == "hello.txt").unwrap().data.as_ref().unwrap();
+    assert!(recovered[..12 * BS].iter().all(|b| *b == 0));
+    assert_eq!(&recovered[12 * BS..12 * BS + 22], b"Hello ext filesystem!\n");
+}