Merge pull request #547 from rust-osdev/fix/large-fat16

don't use BPB_TotSec16 to determine FAT type

Author: Freax13

bios/stage-2/src/fat.rs

@@ -48,16 +48,14 @@ impl Bpb {
         let root_cluster;
         let fat_size_32;
 
-        if (total_sectors_16 == 0) && (total_sectors_32 != 0) {
+        if fat_size_16 == 0 {
             // FAT32
             fat_size_32 = u32::from_le_bytes(raw[36..40].try_into().unwrap());
             root_cluster = u32::from_le_bytes(raw[44..48].try_into().unwrap());
-        } else if (total_sectors_16 != 0) && (total_sectors_32 == 0) {
+        } else {
             // FAT12 or FAT16
             fat_size_32 = 0;
             root_cluster = 0;
-        } else {
-            panic!("ExactlyOneTotalSectorsFieldMustBeZero");
         }
 
         Self {

tests/ramdisk.rs

@@ -1,6 +1,8 @@
 use std::path::Path;
 
 use bootloader_test_runner::run_test_kernel_with_ramdisk;
+use tempfile::NamedTempFile;
+
 static RAMDISK_PATH: &str = "tests/ramdisk.txt";
 
 #[test]
@@ -26,3 +28,15 @@ fn memory_map() {
         Some(Path::new(RAMDISK_PATH)),
     );
 }
+
+#[test]
+fn large_ramdisk() {
+    // Create a large file to act as the RAM disk.
+    let ramdisk = NamedTempFile::new().unwrap();
+    ramdisk.as_file().set_len(1024 * 1024 * 16).unwrap();
+
+    run_test_kernel_with_ramdisk(
+        env!("CARGO_BIN_FILE_TEST_KERNEL_RAMDISK_large_ramdisk"),
+        Some(ramdisk.as_ref()),
+    );
+}

tests/test_kernels/ramdisk/src/bin/large_ramdisk.rs

@@ -0,0 +1,24 @@
+#![no_std] // don't link the Rust standard library
+#![no_main] // disable all Rust-level entry points
+
+use bootloader_api::{BootInfo, entry_point};
+use core::fmt::Write;
+use test_kernel_ramdisk::{QemuExitCode, exit_qemu, serial};
+
+entry_point!(kernel_main);
+
+fn kernel_main(boot_info: &'static mut BootInfo) -> ! {
+    writeln!(serial(), "Boot info: {boot_info:?}").unwrap();
+    assert!(boot_info.ramdisk_addr.into_option().is_some());
+    writeln!(serial(), "RAM disk size: {}", boot_info.ramdisk_len).unwrap();
+
+    exit_qemu(QemuExitCode::Success);
+}
+
+/// This function is called on panic.
+#[cfg(not(test))]
+#[panic_handler]
+fn panic(info: &core::panic::PanicInfo) -> ! {
+    let _ = writeln!(test_kernel_ramdisk::serial(), "PANIC: {info}");
+    exit_qemu(QemuExitCode::Failed);
+}