Update FAT32 FSInfo after root dir allocation

Cargo.toml

@@ -47,3 +47,4 @@ chrono = { version = "0.4", default-features = false, features = ["clock"], opti
 [dev-dependencies]
 env_logger = "0.9"
 fscommon = "0.1"
+tempfile = "3.24.0"

src/fs.rs

@@ -1173,16 +1173,6 @@ pub fn format_volume<S: ReadWriteSeek>(storage: &mut S, options: FormatVolumeOpt
 
     let bpb = &boot.bpb;
     if bpb.is_fat32() {
-        // FSInfo sector
-        let fs_info_sector = FsInfoSector {
-            free_cluster_count: None,
-            next_free_cluster: None,
-            dirty: false,
-        };
-        storage.seek(SeekFrom::Start(bpb.bytes_from_sectors(bpb.fs_info_sector())))?;
-        fs_info_sector.serialize(storage)?;
-        write_zeros_until_end_of_sector(storage, bytes_per_sector)?;
-
         // backup boot sector
         storage.seek(SeekFrom::Start(bpb.bytes_from_sectors(bpb.backup_boot_sector())))?;
         boot.serialize(storage)?;
@@ -1220,6 +1210,16 @@ pub fn format_volume<S: ReadWriteSeek>(storage: &mut S, options: FormatVolumeOpt
         let fat32_root_dir_pos = bpb.bytes_from_sectors(fat32_root_dir_first_sector);
         storage.seek(SeekFrom::Start(fat32_root_dir_pos))?;
         write_zeros(storage, u64::from(bpb.cluster_size()))?;
+
+        let free_cluster_count = bpb.total_clusters() - 1;
+        let fs_info_sector = FsInfoSector {
+            free_cluster_count: Some(free_cluster_count),
+            next_free_cluster: Some(root_dir_first_cluster + 1),
+            dirty: false,
+        };
+        storage.seek(SeekFrom::Start(bpb.bytes_from_sectors(bpb.fs_info_sector())))?;
+        fs_info_sector.serialize(storage)?;
+        write_zeros_until_end_of_sector(storage, bytes_per_sector)?;
     }
 
     // Create volume label directory entry if volume label is specified in options

tests/fsck.rs

@@ -1,27 +1,32 @@
 #![cfg(target_os = "linux")]
-use fatfs::Write;
+
+use fatfs::{FatType, Write};
 
 const KB: u32 = 1024;
 const MB: u32 = KB * 1024;
 
-#[test]
-fn test_fsck_1mb() {
-    let _ = env_logger::builder().is_test(true).try_init();
+fn create_and_fsck_image(fat_type: FatType, size: u32) {
+    let mut disk_img =
+        tempfile::NamedTempFile::with_suffix(format!("-{fat_type:?}-{size}.img")).expect("create named tempfile");
+    let disk_img_path = disk_img.path().display().to_string();
 
-    let mut image = std::fs::OpenOptions::new()
-        .write(true)
-        .read(true)
-        .create(true)
-        .open("/tmp/test.img")
-        .expect("open temporary image file");
-    image.set_len(MB as u64).expect("set_len on temp file");
+    let image = disk_img.as_file_mut();
+    image.set_len(size as u64).expect("set_len on temp file");
 
     fatfs::format_volume(
         &mut fatfs::StdIoWrapper::from(image.try_clone().expect("clone tempfile")),
-        fatfs::FormatVolumeOptions::new().total_sectors(MB / 512),
+        fatfs::FormatVolumeOptions::new()
+            .fat_type(fat_type)
+            .total_sectors(size / 512),
     )
     .expect("format volume");
 
+    let fsck_status = std::process::Command::new("fsck.vfat")
+        .args(&["-y", &disk_img_path])
+        .status()
+        .expect("get fsck.vfat status");
+    assert!(fsck_status.success(), "fsck was not successful ({fsck_status:?})");
+
     let fs = fatfs::FileSystem::new(image, fatfs::FsOptions::new()).expect("open fs");
     fs.root_dir().create_dir("dir1").expect("create dir1");
     fs.root_dir()
@@ -39,10 +44,22 @@ fn test_fsck_1mb() {
     core::mem::drop(fs);
 
     let fsck_status = std::process::Command::new("fsck.vfat")
-        .args(&["-n", "/tmp/test.img"])
-        .spawn()
-        .expect("spawn fsck")
-        .wait()
-        .expect("wait on fsck");
+        .args(&["-y", &disk_img_path])
+        .status()
+        .expect("get fsck.vfat status");
     assert!(fsck_status.success(), "fsck was not successful ({fsck_status:?})");
 }
+
+#[test]
+fn test_fsck_1mb_fat12() {
+    let _ = env_logger::builder().is_test(true).try_init();
+
+    create_and_fsck_image(FatType::Fat12, MB);
+}
+
+#[test]
+fn test_fsck_33mb_fat32() {
+    let _ = env_logger::builder().is_test(true).try_init();
+
+    create_and_fsck_image(FatType::Fat32, 33 * MB);
+}