Add a unstable-disable-block-count-check feature that removes the block count check

Upstream PR: https://github.com/littlefs-project/littlefs/pull/584 introduced a check
that the block count matches the superblock.

However that can cause some issues for filesystem that were formatted with a wrong block count
and later corrected.

Cargo.toml

@@ -19,3 +19,5 @@ trace = []
 malloc = []
 software-intrinsics = []
 multiversion = []
+
+unstable-disable-block-count-check = []

build.rs

@@ -1,14 +1,61 @@
 use std::env;
 use std::path::PathBuf;
+use std::process::Command;
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
+
+    // Patch lfs.h to remove the lfs_util import because clang fails to locate the
+    // libraries for the custom target (especially string.h)
+    // Compilation before that succeeds because it's using gcc,
+    // which comes as a distribution with these utils.
+    // Turns out lfs_utils is not used in lfs.h, and clang properly finds stdint.h and stdbool,
+    // but not string.h
+    let lfs_h = std::fs::read_to_string("littlefs/lfs.h").expect("Reading lfs.h succeeds");
+    println!("cargo::rerun-if-changed=littlefs/lfs.h");
+    let out_lfs_h = out_path.join("lfs.h");
+    std::fs::write(
+        &out_lfs_h,
+        lfs_h.replace(
+            r##"#include "lfs_util.h""##,
+            "#include <stdint.h>\n#include <stdbool.h>",
+        ),
+    )
+    .expect("Failed to write lfs.h");
+
+    // maybe patch lfs.c to remove the mount check for the block count
+    println!("cargo::rerun-if-changed=littlefs/lfs.c");
+    let out_lfs_c = out_path.join("lfs.c");
+    if cfg!(feature = "unstable-disable-block-count-check") {
+        println!("cargo::rerun-if-changed=remove-mount-check.patch");
+        assert!(
+            Command::new("patch")
+                .args([
+                    "littlefs/lfs.c",
+                    "-o",
+                    out_lfs_c.to_str().unwrap(),
+                    "remove-mount-check.patch"
+                ])
+                .spawn()
+                .unwrap()
+                .wait()
+                .unwrap()
+                .success(),
+            "Failed to apply patch"
+        )
+    } else {
+        std::fs::copy("littlefs/lfs.c", out_path.join("lfs.c")).unwrap();
+    }
+
     let mut builder = cc::Build::new();
     let builder = builder
         .flag("-std=c99")
         .flag("-DLFS_NO_DEBUG")
         .flag("-DLFS_NO_WARN")
         .flag("-DLFS_NO_ERROR")
-        .file("littlefs/lfs.c")
+        .include(&out_path)
+        .include("littlefs")
+        .file(out_lfs_c)
         .file("littlefs/lfs_util.c")
         .file("string.c");
 
@@ -29,25 +76,6 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     builder.compile("lfs-sys");
 
-    // Patch lfs.h to remove the lfs_util import because clang fails to locate the
-    // libraries for the custom target (especially string.h)
-    // Compilation before that succeeds because it's using gcc,
-    // which comes as a distribution with these utils.
-    // Turns out lfs_utils is not used in lfs.h, and clang properly finds stdint.h and stdbool,
-    // but not string.h
-    let lfs_h = std::fs::read_to_string("littlefs/lfs.h").expect("Reading lfs.h succeeds");
-    println!("cargo::rerun-if-changed=littlefs/lfs.h");
-    let out_path = PathBuf::from(env::var("OUT_DIR").unwrap());
-    let out_lfs_h = out_path.join("lfs.h");
-    std::fs::write(
-        &out_lfs_h,
-        lfs_h.replace(
-            r##"#include "lfs_util.h""##,
-            "#include <stdint.h>\n#include <stdbool.h>",
-        ),
-    )
-    .expect("Failed to write lfs.h");
-
     let bindgen = bindgen::Builder::default()
         .header(out_lfs_h.into_os_string().into_string().unwrap())
         .clang_arg("-std=c99")

remove-mount-check.patch

@@ -0,0 +1,31 @@
+--- lfs.c	2025-04-14 12:03:45.959258416 +0200
++++ lfs.c.patched	2025-04-14 12:03:23.044370382 +0200
+@@ -4521,15 +4521,20 @@
+             }
+ 
+             // this is where we get the block_count from disk if block_count=0
+-            if (lfs->cfg->block_count
+-                    && superblock.block_count != lfs->cfg->block_count) {
+-                LFS_ERROR("Invalid block count (%"PRIu32" != %"PRIu32")",
+-                        superblock.block_count, lfs->cfg->block_count);
+-                err = LFS_ERR_INVAL;
+-                goto cleanup;
+-            }
++            // 
++            // if (lfs->cfg->block_count
++            //         && superblock.block_count != lfs->cfg->block_count) {
++            //     LFS_ERROR("Invalid block count (%"PRIu32" != %"PRIu32")",
++            //             superblock.block_count, lfs->cfg->block_count);
++            //     err = LFS_ERR_INVAL;
++            //     goto cleanup;
++            // }
+ 
+-            lfs->block_count = superblock.block_count;
++            if (lfs->cfg->block_count) {
++                lfs->block_count = lfs->cfg->block_count;
++            } else {
++                lfs->block_count = superblock.block_count;
++            }
+ 
+             if (superblock.block_size != lfs->cfg->block_size) {
+                 LFS_ERROR("Invalid block size (%"PRIu32" != %"PRIu32")",