From fec3af5e76e62c90cd33bc9e7c177b51bd844e65 Mon Sep 17 00:00:00 2001
From: Jonathan 'theJPster' Pallant <github@thejpster.org.uk>
Date: Sun, 17 Dec 2023 17:19:53 +0000
Subject: [PATCH 1/2] Add example which tries to totally fill the root
 directory.

---
 examples/big_dir.rs | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 examples/big_dir.rs

diff --git a/examples/big_dir.rs b/examples/big_dir.rs
new file mode 100644
index 0000000..b355c3c
--- /dev/null
+++ b/examples/big_dir.rs
@@ -0,0 +1,39 @@
+extern crate embedded_sdmmc;
+
+mod linux;
+use linux::*;
+
+use embedded_sdmmc::{Error, VolumeManager};
+
+fn main() -> Result<(), embedded_sdmmc::Error<std::io::Error>> {
+    env_logger::init();
+    let mut args = std::env::args().skip(1);
+    let filename = args.next().unwrap_or_else(|| "/dev/mmcblk0".into());
+    let print_blocks = args.find(|x| x == "-v").map(|_| true).unwrap_or(false);
+    let lbd = LinuxBlockDevice::new(filename, print_blocks).map_err(Error::DeviceError)?;
+    let mut volume_mgr: VolumeManager<LinuxBlockDevice, Clock, 8, 8, 4> =
+        VolumeManager::new_with_limits(lbd, Clock, 0xAA00_0000);
+    let mut volume = volume_mgr
+        .open_volume(embedded_sdmmc::VolumeIdx(1))
+        .unwrap();
+    println!("Volume: {:?}", volume);
+    let mut root_dir = volume.open_root_dir().unwrap();
+
+    let mut file_num = 0;
+    loop {
+        file_num += 1;
+        let file_name = format!("{}.da", file_num);
+        println!("opening file {file_name} for writing");
+        let mut file = root_dir
+            .open_file_in_dir(
+                file_name.as_str(),
+                embedded_sdmmc::Mode::ReadWriteCreateOrTruncate,
+            )
+            .unwrap();
+        let buf = b"hello world, from rust";
+        println!("writing to file");
+        file.write(&buf[..]).unwrap();
+        println!("closing file");
+        drop(file);
+    }
+}

From 819a624488297ecbf7992c39753a6b7ccb0a307e Mon Sep 17 00:00:00 2001
From: Jonathan 'theJPster' Pallant <github@thejpster.org.uk>
Date: Sun, 17 Dec 2023 17:21:45 +0000
Subject: [PATCH 2/2] Fix issue #74

Map ROOT_DIR (0xFFFF_FFFC) to an actual cluster number, so if you go off the end of the first cluster of the root directory on FAT32, the code no longer crashes trying to convert the ROOT_DIR magic cluster number into a disk offset.
---
 src/fat/volume.rs | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/fat/volume.rs b/src/fat/volume.rs
index c946ec8..b6dd510 100644
--- a/src/fat/volume.rs
+++ b/src/fat/volume.rs
@@ -179,6 +179,9 @@ impl FatVolume {
     where
         D: BlockDevice,
     {
+        if cluster.0 > (u32::MAX / 4) {
+            panic!("next_cluster called on invalid cluster {:x?}", cluster);
+        }
         match &self.fat_specific_info {
             FatSpecificInfo::Fat16(_fat16_info) => {
                 let fat_offset = cluster.0 * 2;
@@ -360,19 +363,24 @@ impl FatVolume {
             FatSpecificInfo::Fat32(fat32_info) => {
                 // All directories on FAT32 have a cluster chain but the root
                 // dir starts in a specified cluster.
-                let mut first_dir_block_num = match dir.cluster {
-                    ClusterId::ROOT_DIR => self.cluster_to_block(fat32_info.first_root_dir_cluster),
-                    _ => self.cluster_to_block(dir.cluster),
+                let mut current_cluster = match dir.cluster {
+                    ClusterId::ROOT_DIR => Some(fat32_info.first_root_dir_cluster),
+                    _ => Some(dir.cluster),
                 };
-                let mut current_cluster = Some(dir.cluster);
+                let mut first_dir_block_num = self.cluster_to_block(dir.cluster);
                 let mut blocks = [Block::new()];
 
                 let dir_size = BlockCount(u32::from(self.blocks_per_cluster));
+                // Walk the cluster chain until we run out of clusters
                 while let Some(cluster) = current_cluster {
+                    // Loop through the blocks in the cluster
                     for block in first_dir_block_num.range(dir_size) {
+                        // Read a block of directory entries
                         block_device
                             .read(&mut blocks, block, "read_dir")
                             .map_err(Error::DeviceError)?;
+                        // Are any entries in the block we just loaded blank? If so
+                        // we can use them.
                         for entry in 0..Block::LEN / OnDiskDirEntry::LEN {
                             let start = entry * OnDiskDirEntry::LEN;
                             let end = (entry + 1) * OnDiskDirEntry::LEN;
@@ -397,6 +405,8 @@ impl FatVolume {
                             }
                         }
                     }
+                    // Well none of the blocks in that cluster had any space in
+                    // them, let's fetch another one.
                     let mut block_cache = BlockCache::empty();
                     current_cluster =
                         match self.next_cluster(block_device, cluster, &mut block_cache) {
@@ -412,6 +422,8 @@ impl FatVolume {
                             _ => None,
                         };
                 }
+                // We ran out of clusters in the chain, and apparently we weren't
+                // able to make the chain longer, so the disk must be full.
                 Err(Error::NotEnoughSpace)
             }
         }