Add FAT12/16/32 scheme daemon, management tools, and build integration

5-crate Rust workspace implementing full VFAT support: fatd scheme daemon (FSScheme with open/read/write/mkdir/unlink/rename/fstat), fat-mkfs (create FAT12/16/32 with labels and cluster size), fat-label (read/write BPB + root-dir volume labels), fat-check (verify + repair dirty flags, FSInfo, lost clusters, orphaned LFN). 60 unit tests, 0 unwrap in production code. Included in all 5 redbear configs via redbear-device-services.toml. Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
2026-04-18 00:13:34 +01:00
parent f6ee40326b
commit 9d1954e0c4
19 changed files with 3703 additions and 1 deletions
@@ -0,0 +1,25 @@
+[workspace]
+members = [
+    "fat-blockdev",
+    "fatd",
+    "fat-mkfs",
+    "fat-label",
+    "fat-check",
+]
+resolver = "3"
+
+[workspace.package]
+version = "0.1.0"
+edition = "2024"
+license = "MIT"
+
+[workspace.dependencies]
+fatfs = "0.3.6"
+fscommon = "0.1.1"
+redox_syscall = "0.7.3"
+redox-scheme = "0.11.0"
+libredox = "0.1.13"
+redox-path = "0.3.0"
+log = "0.4"
+env_logger = "0.11"
+libc = "0.2"
@@ -0,0 +1,22 @@
+[package]
+name = "fat-blockdev"
+description = "Block device adapter for fatfs crate on Redox OS"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[dependencies]
+fatfs.workspace = true
+log.workspace = true
+
+[dependencies.redox_syscall]
+workspace = true
+optional = true
+
+[dependencies.libredox]
+workspace = true
+optional = true
+
+[features]
+default = ["redox"]
+redox = ["dep:redox_syscall", "dep:libredox"]
@@ -0,0 +1,72 @@
+use std::fs::{File, OpenOptions};
+use std::io::{self, Read, Seek, SeekFrom, Write};
+use std::path::Path;
+
+/// Block device adapter backed by a host file (Linux/macOS).
+///
+/// Implements `Read + Write + Seek` for use with the `fatfs` crate.
+/// Wraps `std::fs::File` and reports total size from filesystem metadata.
+pub struct FileDisk {
+    file: File,
+    size: u64,
+}
+
+impl FileDisk {
+    /// Open an existing file for read/write.
+    pub fn new(file: File) -> Self {
+        let size = file.metadata()
+            .map(|m| m.len())
+            .unwrap_or_else(|e| {
+                log::warn!("file_disk: metadata read failed, assuming zero size: {e}");
+                0
+            });
+        Self { file, size }
+    }
+
+    pub fn open<P: AsRef<Path>>(path: P) -> io::Result<Self> {
+        let file = OpenOptions::new()
+            .read(true)
+            .write(true)
+            .open(path)?;
+        let size = file.metadata()?.len();
+        Ok(Self { file, size })
+    }
+
+    /// Create a new file of the given size, zero-filled.
+    pub fn create<P: AsRef<Path>>(path: P, size: u64) -> io::Result<Self> {
+        let file = File::create(&path)?;
+        file.set_len(size)?;
+        let file = OpenOptions::new()
+            .read(true)
+            .write(true)
+            .open(&path)?;
+        Ok(Self { file, size })
+    }
+
+    /// Total size of the backing file in bytes.
+    pub fn size(&self) -> u64 {
+        self.size
+    }
+}
+
+impl Read for FileDisk {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        self.file.read(buf)
+    }
+}
+
+impl Write for FileDisk {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        self.file.write(buf)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.file.flush()
+    }
+}
+
+impl Seek for FileDisk {
+    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
+        self.file.seek(pos)
+    }
+}
@@ -0,0 +1,9 @@
+mod file_disk;
+
+pub use file_disk::FileDisk;
+
+#[cfg(feature = "redox")]
+mod redox_disk;
+
+#[cfg(feature = "redox")]
+pub use redox_disk::RedoxDisk;
@@ -0,0 +1,55 @@
+use std::io::{self, Read, Seek, SeekFrom, Write};
+
+pub struct RedoxDisk {
+    fd: usize,
+    size: u64,
+}
+
+impl RedoxDisk {
+    pub fn open(disk_path: &str) -> syscall::error::Result<Self> {
+        let fd = libredox::call::open(disk_path, libredox::flag::O_RDWR, 0)?;
+        let mut stat = syscall::data::Stat::default();
+        syscall::call::fstat(fd, &mut stat)?;
+        Ok(Self {
+            fd,
+            size: stat.st_size,
+        })
+    }
+
+    pub fn size(&self) -> u64 {
+        self.size
+    }
+}
+
+impl Read for RedoxDisk {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        syscall::call::read(self.fd, buf)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, format!("redox read: {e:?}")))
+    }
+}
+
+impl Write for RedoxDisk {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        syscall::call::write(self.fd, buf)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, format!("redox write: {e:?}")))
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        syscall::call::fsync(self.fd)
+            .map(|_| ())
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, format!("redox flush: {e:?}")))
+    }
+}
+
+impl Seek for RedoxDisk {
+    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
+        let offset = match pos {
+            SeekFrom::Start(off) => off as isize,
+            SeekFrom::Current(off) => off as isize,
+            SeekFrom::End(off) => (self.size as isize) + (off as isize),
+        };
+        let result = syscall::call::lseek(self.fd, offset, syscall::flag::SEEK_SET)
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, format!("redox seek: {e:?}")))?;
+        Ok(result as u64)
+    }
+}
@@ -0,0 +1,16 @@
+[package]
+name = "fat-check"
+description = "FAT filesystem checker (fsck.fat equivalent)"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[[bin]]
+name = "fat-check"
+path = "src/main.rs"
+
+[dependencies]
+fat-blockdev = { path = "../fat-blockdev" }
+fatfs.workspace = true
+fscommon.workspace = true
+log.workspace = true
@@ -0,0 +1,16 @@
+[package]
+name = "fat-label"
+description = "Read and write FAT volume labels (fatlabel equivalent)"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[[bin]]
+name = "fat-label"
+path = "src/main.rs"
+
+[dependencies]
+fat-blockdev = { path = "../fat-blockdev" }
+fatfs.workspace = true
+fscommon.workspace = true
+log.workspace = true
@@ -0,0 +1,436 @@
+use std::env;
+use std::io::{Read, Seek, SeekFrom, Write};
+use std::process;
+
+use fat_blockdev::FileDisk;
+use fatfs::FsOptions;
+
+fn usage() -> ! {
+    eprintln!("Usage: fat-label [-s <label>|--set <label>] <device>");
+    process::exit(1)
+}
+
+fn printable_label(label: &str) -> String {
+    if label.is_empty() {
+        "(no label)".to_string()
+    } else {
+        label.to_string()
+    }
+}
+
+fn invalid_volume_label_char(byte: u8) -> bool {
+    matches!(
+        byte,
+        0x00..=0x1F
+            | 0x7F
+            | b'"'
+            | b'*'
+            | b'+'
+            | b','
+            | b'.'
+            | b'/'
+            | b':'
+            | b';'
+            | b'<'
+            | b'='
+            | b'>'
+            | b'?'
+            | b'['
+            | b'\\'
+            | b']'
+            | b'|'
+    )
+}
+
+fn normalize_label(label: &str) -> [u8; 11] {
+    if !label.is_ascii() {
+        eprintln!("fat-label: label must contain only ASCII characters");
+        process::exit(1);
+    }
+
+    if label.len() > 11 {
+        eprintln!("fat-label: label too long (max 11 chars)");
+        process::exit(1);
+    }
+
+    let label = label.to_ascii_uppercase();
+    if let Some(invalid) = label.bytes().find(|byte| invalid_volume_label_char(*byte)) {
+        eprintln!("fat-label: invalid character '{}' in label", invalid as char);
+        process::exit(1);
+    }
+
+    let mut bytes = [b' '; 11];
+    for (index, byte) in label.bytes().enumerate() {
+        bytes[index] = byte;
+    }
+    bytes
+}
+
+fn label_string(bytes: &[u8; 11]) -> String {
+    String::from_utf8_lossy(bytes)
+        .trim_end_matches(' ')
+        .to_string()
+}
+
+fn read_volume_label(device: &str) -> String {
+    let disk = FileDisk::open(device).unwrap_or_else(|e| {
+        eprintln!("fat-label: failed to open {device}: {e}");
+        process::exit(1);
+    });
+
+    let buf_disk = fscommon::BufStream::new(disk);
+    let fs = fatfs::FileSystem::new(buf_disk, FsOptions::new()).unwrap_or_else(|e| {
+        eprintln!("fat-label: failed to mount {device}: {e}");
+        process::exit(1);
+    });
+
+    fs.volume_label()
+}
+
+fn write_volume_label(device: &str, label: [u8; 11]) {
+    let mut disk = FileDisk::open(device).unwrap_or_else(|e| {
+        eprintln!("fat-label: failed to open {device}: {e}");
+        process::exit(1);
+    });
+
+    let mut boot_sector = [0u8; 512];
+    disk.seek(SeekFrom::Start(0))
+        .and_then(|_| disk.read_exact(&mut boot_sector))
+        .unwrap_or_else(|e| {
+            eprintln!("fat-label: failed to read BPB from {device}: {e}");
+            process::exit(1);
+        });
+
+    if boot_sector[510] != 0x55 || boot_sector[511] != 0xAA {
+        eprintln!(
+            "fat-label: invalid boot sector signature {:02X} {:02X}",
+            boot_sector[510], boot_sector[511]
+        );
+        process::exit(1);
+    }
+
+    let root_entry_count = u16::from_le_bytes([boot_sector[17], boot_sector[18]]);
+    let fat_size_32 = u32::from_le_bytes([
+        boot_sector[36],
+        boot_sector[37],
+        boot_sector[38],
+        boot_sector[39],
+    ]);
+    let label_offset = if root_entry_count == 0 && fat_size_32 != 0 {
+        71
+    } else {
+        43
+    };
+
+    disk.seek(SeekFrom::Start(label_offset))
+        .and_then(|_| disk.write_all(&label))
+        .and_then(|_| disk.flush())
+        .unwrap_or_else(|e| {
+            eprintln!("fat-label: failed to write BPB volume label to {device}: {e}");
+            process::exit(1);
+        });
+
+    drop(disk);
+
+    update_root_dir_label(device, label, &boot_sector);
+}
+
+fn update_root_dir_label(device: &str, label: [u8; 11], boot_sector: &[u8; 512]) {
+    let root_entry_count = u16::from_le_bytes([boot_sector[17], boot_sector[18]]) as u32;
+    let bytes_per_sector = u16::from_le_bytes([boot_sector[11], boot_sector[12]]) as u32;
+    let sectors_per_cluster = boot_sector[13] as u32;
+    let reserved_sectors = u16::from_le_bytes([boot_sector[14], boot_sector[15]]) as u32;
+    let num_fats = boot_sector[16] as u32;
+    let fat_size_16 = u16::from_le_bytes([boot_sector[22], boot_sector[23]]) as u32;
+    let fat_size_32 = u32::from_le_bytes([boot_sector[36], boot_sector[37], boot_sector[38], boot_sector[39]]);
+    let fat_size = if fat_size_32 != 0 && root_entry_count == 0 { fat_size_32 } else { fat_size_16 };
+    let root_dir_sectors = (root_entry_count * 32).div_ceil(bytes_per_sector);
+    let first_root_dir_sector = reserved_sectors + num_fats * fat_size;
+    let root_cluster = u32::from_le_bytes([boot_sector[44], boot_sector[45], boot_sector[46], boot_sector[47]]);
+
+    let mut disk = FileDisk::open(device).unwrap_or_else(|e| {
+        eprintln!("fat-label: failed to reopen {device} for root dir update: {e}");
+        process::exit(1);
+    });
+
+    let is_fat32 = root_entry_count == 0 && fat_size_32 != 0;
+
+    let mut new_entry = [0u8; 32];
+    new_entry[0..11].copy_from_slice(&label);
+    new_entry[11] = 0x08;
+
+    if is_fat32 {
+        let first_data_sector = first_root_dir_sector + root_dir_sectors;
+        let cluster_offset = |cluster: u32| -> u64 {
+            let first_sector = first_data_sector + (cluster - 2) * sectors_per_cluster;
+            u64::from(first_sector) * u64::from(bytes_per_sector)
+        };
+
+        let mut found = false;
+        let mut first_free_offset: Option<u64> = None;
+        let mut cluster = root_cluster;
+        let cluster_size = (bytes_per_sector * sectors_per_cluster) as usize;
+        loop {
+            let offset = cluster_offset(cluster);
+            let mut buf = vec![0u8; cluster_size];
+            disk.seek(SeekFrom::Start(offset))
+                .and_then(|_| disk.read_exact(&mut buf))
+                .unwrap_or_else(|e| {
+                    eprintln!("fat-label: failed to read root dir cluster: {e}");
+                    process::exit(1);
+                });
+
+            for (i, chunk) in buf.chunks_exact(32).enumerate() {
+                if chunk[0] == 0x00 {
+                    if first_free_offset.is_none() {
+                        first_free_offset = Some(offset + (i as u64 * 32));
+                    }
+                    break;
+                }
+                if chunk[0] == 0xE5 {
+                    if first_free_offset.is_none() {
+                        first_free_offset = Some(offset + (i as u64 * 32));
+                    }
+                    continue;
+                }
+                if chunk[11] == 0x08 {
+                    let entry_offset = offset + (i as u64 * 32);
+                    disk.seek(SeekFrom::Start(entry_offset))
+                        .and_then(|_| disk.write_all(&label))
+                        .and_then(|_| disk.flush())
+                        .unwrap_or_else(|e| {
+                            eprintln!("fat-label: failed to write root dir label entry: {e}");
+                            process::exit(1);
+                        });
+                    found = true;
+                    break;
+                }
+            }
+            if found {
+                break;
+            }
+
+            let fat_offset = cluster as usize * 4;
+            let fat_byte_offset = reserved_sectors as u64 * bytes_per_sector as u64;
+            let mut fat_entry = [0u8; 4];
+            disk.seek(SeekFrom::Start(fat_byte_offset + fat_offset as u64))
+                .and_then(|_| disk.read_exact(&mut fat_entry))
+                .unwrap_or_else(|e| {
+                    eprintln!("fat-label: failed to read FAT entry: {e}");
+                    process::exit(1);
+                });
+            let next = u32::from_le_bytes(fat_entry) & 0x0FFF_FFFF;
+            if next >= 0x0FFF_FFF8 {
+                break;
+            }
+            cluster = next;
+        }
+
+        if !found {
+            if let Some(free_offset) = first_free_offset {
+                disk.seek(SeekFrom::Start(free_offset))
+                    .and_then(|_| disk.write_all(&new_entry))
+                    .and_then(|_| disk.flush())
+                    .unwrap_or_else(|e| {
+                        eprintln!("fat-label: failed to create root dir label entry: {e}");
+                        process::exit(1);
+                    });
+            } else {
+                eprintln!("fat-label: warning: root directory full, BPB label updated but no root-dir entry created");
+            }
+        }
+    } else {
+        let root_dir_offset = u64::from(first_root_dir_sector) * u64::from(bytes_per_sector);
+        let root_dir_size = (root_entry_count * 32) as usize;
+        let mut buf = vec![0u8; root_dir_size];
+        disk.seek(SeekFrom::Start(root_dir_offset))
+            .and_then(|_| disk.read_exact(&mut buf))
+            .unwrap_or_else(|e| {
+                eprintln!("fat-label: failed to read root dir: {e}");
+                process::exit(1);
+            });
+
+        let mut found = false;
+        let mut first_free_offset: Option<u64> = None;
+
+        for (i, chunk) in buf.chunks_exact(32).enumerate() {
+            if chunk[0] == 0x00 {
+                if first_free_offset.is_none() {
+                    first_free_offset = Some(root_dir_offset + (i as u64 * 32));
+                }
+                break;
+            }
+            if chunk[0] == 0xE5 {
+                if first_free_offset.is_none() {
+                    first_free_offset = Some(root_dir_offset + (i as u64 * 32));
+                }
+                continue;
+            }
+            if chunk[11] == 0x08 {
+                let entry_offset = root_dir_offset + (i as u64 * 32);
+                disk.seek(SeekFrom::Start(entry_offset))
+                    .and_then(|_| disk.write_all(&label))
+                    .and_then(|_| disk.flush())
+                    .unwrap_or_else(|e| {
+                        eprintln!("fat-label: failed to write root dir label entry: {e}");
+                        process::exit(1);
+                    });
+                found = true;
+                break;
+            }
+        }
+
+        if !found {
+            if let Some(free_offset) = first_free_offset {
+                disk.seek(SeekFrom::Start(free_offset))
+                    .and_then(|_| disk.write_all(&new_entry))
+                    .and_then(|_| disk.flush())
+                    .unwrap_or_else(|e| {
+                        eprintln!("fat-label: failed to create root dir label entry: {e}");
+                        process::exit(1);
+                    });
+            } else {
+                eprintln!("fat-label: warning: root directory full, BPB label updated but no root-dir entry created");
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Test invalid_volume_label_char
+    #[test]
+    fn test_invalid_volume_label_char_valid_range() {
+        // A-Z, 0-9 are valid
+        assert!(!invalid_volume_label_char(b'A'));
+        assert!(!invalid_volume_label_char(b'Z'));
+        assert!(!invalid_volume_label_char(b'0'));
+        assert!(!invalid_volume_label_char(b'9'));
+    }
+
+    #[test]
+    fn test_invalid_volume_label_char_invalid_chars() {
+        // Control chars 0x00-0x1F
+        assert!(invalid_volume_label_char(0x00));
+        assert!(invalid_volume_label_char(0x1F));
+        assert!(invalid_volume_label_char(0x7F));
+        // Invalid symbols
+        assert!(invalid_volume_label_char(b'"'));
+        assert!(invalid_volume_label_char(b'*'));
+        assert!(invalid_volume_label_char(b'+'));
+        assert!(invalid_volume_label_char(b','));
+        assert!(invalid_volume_label_char(b'.'));
+        assert!(invalid_volume_label_char(b'/'));
+        assert!(invalid_volume_label_char(b':'));
+        assert!(invalid_volume_label_char(b';'));
+        assert!(invalid_volume_label_char(b'<'));
+        assert!(invalid_volume_label_char(b'='));
+        assert!(invalid_volume_label_char(b'>'));
+        assert!(invalid_volume_label_char(b'?'));
+        assert!(invalid_volume_label_char(b'['));
+        assert!(invalid_volume_label_char(b'\\'));
+        assert!(invalid_volume_label_char(b']'));
+        assert!(invalid_volume_label_char(b'|'));
+    }
+
+    // Test label_string
+    #[test]
+    fn test_label_string_trims_trailing_spaces() {
+        let bytes = *b"TEST       ";
+        let result = label_string(&bytes);
+        assert_eq!(result, "TEST");
+    }
+
+    #[test]
+    fn test_label_string_no_trailing_spaces() {
+        let bytes = *b"NOTRIMMED  ";
+        let result = label_string(&bytes);
+        assert_eq!(result, "NOTRIMMED");
+    }
+
+    #[test]
+    fn test_label_string_all_spaces() {
+        let bytes = *b"           ";
+        let result = label_string(&bytes);
+        assert_eq!(result, "");
+    }
+
+    // Test printable_label
+    #[test]
+    fn test_printable_label_empty() {
+        let result = printable_label("");
+        assert_eq!(result, "(no label)");
+    }
+
+    #[test]
+    fn test_printable_label_non_empty() {
+        let result = printable_label("MYDISK");
+        assert_eq!(result, "MYDISK");
+    }
+}
+
+fn main() {
+    let mut args = env::args().skip(1);
+    let mut new_label = None;
+    let mut device = None;
+
+    while let Some(arg) = args.next() {
+        match arg.as_str() {
+            "-s" | "--set" => {
+                if new_label.is_some() {
+                    eprintln!("fat-label: volume label already specified");
+                    usage();
+                }
+                new_label = Some(args.next().unwrap_or_else(|| {
+                    eprintln!("fat-label: {} requires a label argument", arg);
+                    process::exit(1);
+                }));
+            }
+            _ if arg.starts_with('-') => {
+                eprintln!("fat-label: unknown option '{arg}'");
+                usage();
+            }
+            _ => {
+                if device.is_some() {
+                    eprintln!("fat-label: unexpected extra argument '{arg}'");
+                    usage();
+                }
+                device = Some(arg);
+            }
+        }
+    }
+
+    let device = device.unwrap_or_else(|| usage());
+
+    match new_label {
+        Some(label) => {
+            let old_label = read_volume_label(&device);
+            let label_bytes = normalize_label(&label);
+            write_volume_label(&device, label_bytes);
+
+            let new_label = read_volume_label(&device);
+            let expected_label = label_string(&label_bytes);
+            if new_label != expected_label {
+                eprintln!(
+                    "fat-label: verification failed: expected '{}', got '{}'",
+                    printable_label(&expected_label),
+                    printable_label(&new_label)
+                );
+                process::exit(1);
+            }
+
+            println!("old label: {}", printable_label(&old_label));
+            println!("new label: {}", printable_label(&new_label));
+        }
+        None => {
+            let label = read_volume_label(&device);
+            if label.is_empty() {
+                println!("(no label)");
+            } else {
+                println!("{label}");
+            }
+        }
+    }
+}
@@ -0,0 +1,15 @@
+[package]
+name = "fat-mkfs"
+description = "Create FAT filesystems (mkfs.fat equivalent)"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[[bin]]
+name = "fat-mkfs"
+path = "src/main.rs"
+
+[dependencies]
+fat-blockdev = { path = "../fat-blockdev" }
+fatfs.workspace = true
+log.workspace = true
@@ -0,0 +1,158 @@
+use std::env;
+use std::fs::OpenOptions;
+use std::process;
+
+use fat_blockdev::FileDisk;
+use fatfs::{FatType, FormatVolumeOptions};
+
+fn usage() -> ! {
+    eprintln!("Usage: fat-mkfs [options] <device>");
+    eprintln!("Options:");
+    eprintln!("  -F <12|16|32>  FAT type (default: auto)");
+    eprintln!("  -n <label>     Volume label (max 11 chars)");
+    eprintln!("  -s <size>      File size in bytes (for file-backed images)");
+    eprintln!("  -c <sectors>   Sectors per cluster (must be power of 2)");
+    process::exit(1)
+}
+
+fn parse_fat_type(s: &str) -> Option<FatType> {
+    match s {
+        "12" => Some(FatType::Fat12),
+        "16" => Some(FatType::Fat16),
+        "32" => Some(FatType::Fat32),
+        _ => None,
+    }
+}
+
+fn main() {
+    let mut args = env::args().skip(1).peekable();
+    let mut fat_type: Option<FatType> = None;
+    let mut label: Option<String> = None;
+    let mut file_size: Option<u64> = None;
+    let mut cluster_sectors: Option<u8> = None;
+
+    while let Some(arg) = args.next() {
+        match arg.as_str() {
+            "-F" => {
+                let val = args.next().unwrap_or_else(|| {
+                    eprintln!("fat-mkfs: -F requires an argument (12, 16, or 32)");
+                    process::exit(1);
+                });
+                fat_type = Some(parse_fat_type(&val).unwrap_or_else(|| {
+                    eprintln!("fat-mkfs: invalid FAT type '{val}', use 12, 16, or 32");
+                    process::exit(1);
+                }));
+            }
+            "-n" => {
+                let val = args.next().unwrap_or_else(|| {
+                    eprintln!("fat-mkfs: -n requires a label argument");
+                    process::exit(1);
+                });
+                if val.len() > 11 {
+                    eprintln!("fat-mkfs: volume label too long (max 11 chars)");
+                    process::exit(1);
+                }
+                label = Some(val.to_uppercase());
+            }
+            "-s" => {
+                let val = args.next().unwrap_or_else(|| {
+                    eprintln!("fat-mkfs: -s requires a size argument");
+                    process::exit(1);
+                });
+                file_size = Some(val.parse::<u64>().unwrap_or_else(|_| {
+                    eprintln!("fat-mkfs: invalid size '{val}'");
+                    process::exit(1);
+                }));
+            }
+            "-c" => {
+                let val = args.next().unwrap_or_else(|| {
+                    eprintln!("fat-mkfs: -c requires a sectors argument");
+                    process::exit(1);
+                });
+                let sc = val.parse::<u8>().unwrap_or_else(|_| {
+                    eprintln!("fat-mkfs: invalid sectors '{val}'");
+                    process::exit(1);
+                });
+                if sc == 0 || (sc & (sc - 1)) != 0 {
+                    eprintln!("fat-mkfs: sectors per cluster must be a power of 2 and greater than 0");
+                    process::exit(1);
+                }
+                cluster_sectors = Some(sc);
+            }
+            other if other.starts_with('-') => {
+                eprintln!("fat-mkfs: unknown option '{other}'");
+                usage();
+            }
+            _ => {
+                let path = arg;
+                if let Some(size) = file_size {
+                    let file = std::fs::File::create(&path)
+                        .unwrap_or_else(|e| {
+                            eprintln!("fat-mkfs: failed to create {path}: {e}");
+                            process::exit(1);
+                        });
+                    // Pre-zero to avoid sparse file issues on some hosts
+                    use std::io::{BufWriter, Write};
+                    let mut writer = BufWriter::new(file);
+                    let zeros = [0u8; 65536];
+                    let mut remaining = size as usize;
+                    while remaining > 0 {
+                        let chunk_size = remaining.min(zeros.len());
+                        writer.write_all(&zeros[..chunk_size]).unwrap_or_else(|e| {
+                            eprintln!("fat-mkfs: failed to zero-fill {path}: {e}");
+                            process::exit(1);
+                        });
+                        remaining -= chunk_size;
+                    }
+                    drop(writer);
+                }
+
+                let file = OpenOptions::new()
+                    .read(true)
+                    .write(true)
+                    .open(&path)
+                    .unwrap_or_else(|e| {
+                        eprintln!("fat-mkfs: failed to open {path}: {e}");
+                        process::exit(1);
+                    });
+
+                let mut options = FormatVolumeOptions::new();
+                if let Some(ft) = fat_type {
+                    options = options.fat_type(ft);
+                }
+                if let Some(ref lbl) = label {
+                    let mut label_bytes = [b' '; 11];
+                    for (i, b) in lbl.bytes().take(11).enumerate() {
+                        label_bytes[i] = b;
+                    }
+                    options = options.volume_label(label_bytes);
+                }
+                if let Some(sc) = cluster_sectors {
+                    options = options.bytes_per_cluster(u32::from(sc) * 512);
+                }
+
+                let mut disk = FileDisk::new(file);
+                fatfs::format_volume(&mut disk, options)
+                    .unwrap_or_else(|e| {
+                        eprintln!("fat-mkfs: format failed: {e}");
+                        process::exit(1);
+                    });
+
+                let type_str = match fat_type {
+                    Some(FatType::Fat12) => "FAT12",
+                    Some(FatType::Fat16) => "FAT16",
+                    Some(FatType::Fat32) => "FAT32",
+                    None => "auto-detected",
+                };
+                let cluster_str = if let Some(sc) = cluster_sectors {
+                    format!(", cluster {} sectors", sc)
+                } else {
+                    String::new()
+                };
+                eprintln!("fat-mkfs: formatted {path} as {type_str}{cluster_str}");
+                return;
+            }
+        }
+    }
+    usage();
+}
@@ -0,0 +1,26 @@
+[package]
+name = "fatd"
+description = "FAT filesystem scheme daemon for Redox OS"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[[bin]]
+name = "fatd"
+path = "src/main.rs"
+
+[dependencies]
+fat-blockdev = { path = "../fat-blockdev" }
+fatfs.workspace = true
+fscommon.workspace = true
+redox_syscall.workspace = true
+redox-scheme.workspace = true
+libredox = { workspace = true, optional = true }
+redox-path = { workspace = true, optional = true }
+log.workspace = true
+env_logger = { workspace = true, optional = true }
+libc.workspace = true
+
+[features]
+default = ["redox"]
+redox = ["dep:libredox", "dep:redox-path", "fat-blockdev/redox", "dep:env_logger"]
@@ -0,0 +1,103 @@
+use syscall::flag::{O_ACCMODE, O_RDONLY, O_RDWR, O_WRONLY};
+
+pub enum Handle {
+    File(FileHandle),
+    Directory(DirectoryHandle),
+    SchemeRoot,
+}
+
+pub struct FileHandle {
+    path: String,
+    offset: u64,
+    flags: usize,
+}
+
+pub struct DirectoryHandle {
+    path: String,
+    entries: Vec<(u64, String, u8)>,
+    cursor: usize,
+    flags: usize,
+}
+
+impl FileHandle {
+    pub fn new(path: String, flags: usize) -> Self {
+        Self {
+            path,
+            offset: 0,
+            flags,
+        }
+    }
+
+    pub fn path(&self) -> &str {
+        &self.path
+    }
+
+    pub fn set_offset(&mut self, offset: u64) {
+        self.offset = offset;
+    }
+
+    pub fn flags(&self) -> usize {
+        self.flags
+    }
+
+    pub fn can_read(&self) -> bool {
+        matches!(self.flags & O_ACCMODE, O_RDONLY | O_RDWR)
+    }
+
+    pub fn can_write(&self) -> bool {
+        matches!(self.flags & O_ACCMODE, O_WRONLY | O_RDWR)
+    }
+
+    pub fn update_path(&mut self, new_path: String) {
+        self.path = new_path;
+    }
+}
+
+impl DirectoryHandle {
+    pub fn new(path: String, entries: Vec<(u64, String, u8)>, flags: usize) -> Self {
+        Self {
+            path,
+            entries,
+            cursor: 0,
+            flags,
+        }
+    }
+
+    pub fn path(&self) -> &str {
+        &self.path
+    }
+
+    pub fn entries(&self) -> &[(u64, String, u8)] {
+        &self.entries
+    }
+
+    pub fn set_cursor(&mut self, cursor: usize) {
+        self.cursor = cursor;
+    }
+
+    pub fn flags(&self) -> usize {
+        self.flags
+    }
+
+    pub fn update_path(&mut self, new_path: String) {
+        self.path = new_path;
+    }
+}
+
+impl Handle {
+    pub fn path(&self) -> Option<&str> {
+        match self {
+            Self::File(handle) => Some(handle.path()),
+            Self::Directory(handle) => Some(handle.path()),
+            Self::SchemeRoot => Some(""),
+        }
+    }
+
+    pub fn flags(&self) -> Option<usize> {
+        match self {
+            Self::File(handle) => Some(handle.flags()),
+            Self::Directory(handle) => Some(handle.flags()),
+            Self::SchemeRoot => None,
+        }
+    }
+}
@@ -0,0 +1,179 @@
+use std::{
+    env,
+    fs::File,
+    io::{self, Read, Write},
+    os::unix::io::{FromRawFd, RawFd},
+    process,
+    sync::atomic::{AtomicUsize, Ordering},
+};
+
+#[cfg(feature = "redox")]
+use fat_blockdev::RedoxDisk as SchemeDisk;
+#[cfg(not(feature = "redox"))]
+use fat_blockdev::FileDisk as SchemeDisk;
+
+mod handle;
+mod mount;
+mod scheme;
+
+pub static IS_UMT: AtomicUsize = AtomicUsize::new(0);
+
+extern "C" fn unmount_handler(_signal: usize) {
+    IS_UMT.store(1, Ordering::SeqCst);
+}
+
+fn install_sigterm_handler() -> io::Result<()> {
+    unsafe {
+        let mut action: libc::sigaction = std::mem::zeroed();
+        if libc::sigemptyset(&mut action.sa_mask) != 0 {
+            return Err(io::Error::last_os_error());
+        }
+        action.sa_flags = 0;
+        action.sa_sigaction = unmount_handler as usize;
+
+        if libc::sigaction(libc::SIGTERM, &action, std::ptr::null_mut()) != 0 {
+            return Err(io::Error::last_os_error());
+        }
+    }
+
+    Ok(())
+}
+
+fn fork_process() -> io::Result<libc::pid_t> {
+    let pid = unsafe { libc::fork() };
+    if pid < 0 {
+        Err(io::Error::last_os_error())
+    } else {
+        Ok(pid)
+    }
+}
+
+fn make_pipe() -> io::Result<[i32; 2]> {
+    let mut pipes = [0; 2];
+    if unsafe { libc::pipe(pipes.as_mut_ptr()) } != 0 {
+        return Err(io::Error::last_os_error());
+    }
+    Ok(pipes)
+}
+
+#[cfg(target_os = "redox")]
+fn capability_mode() {
+    if let Err(err) = libredox::call::setrens(0, 0) {
+        log::error!("fatd: failed to enter null namespace: {err}");
+    }
+}
+
+#[cfg(not(target_os = "redox"))]
+fn capability_mode() {}
+
+fn usage() {
+    eprintln!("fatd [--no-daemon|-d] <disk_path> <mountpoint>");
+}
+
+fn fail_usage(message: &str) -> ! {
+    eprintln!("fatd: {message}");
+    usage();
+    process::exit(1);
+}
+
+fn run_mount(disk_path: &str, mountpoint: &str) -> Result<(), String> {
+    let disk = SchemeDisk::open(disk_path).map_err(|err| format!("failed to open {disk_path}: {err}"))?;
+    let disk = fscommon::BufStream::new(disk);
+    let filesystem = fatfs::FileSystem::new(disk, fatfs::FsOptions::new())
+        .map_err(|err| format!("failed to mount FAT on {disk_path}: {err}"))?;
+
+    mount::mount(filesystem, mountpoint, |mounted_path| {
+        capability_mode();
+        log::info!("mounted FAT filesystem on {disk_path} to {mounted_path}");
+    })
+    .map_err(|err| format!("failed to serve scheme {mountpoint}: {err}"))
+}
+
+fn daemon(disk_path: &str, mountpoint: &str, mut status_pipe: Option<File>) -> i32 {
+    IS_UMT.store(0, Ordering::SeqCst);
+
+    if let Err(err) = install_sigterm_handler() {
+        log::error!("failed to install SIGTERM handler: {err}");
+        if let Some(pipe) = status_pipe.as_mut() {
+            let _ = pipe.write_all(&[1]);
+        }
+        return 1;
+    }
+
+    match run_mount(disk_path, mountpoint) {
+        Ok(()) => {
+            if let Some(pipe) = status_pipe.as_mut() {
+                let _ = pipe.write_all(&[0]);
+            }
+            0
+        }
+        Err(err) => {
+            log::error!("{err}");
+            if let Some(pipe) = status_pipe.as_mut() {
+                let _ = pipe.write_all(&[1]);
+            }
+            1
+        }
+    }
+}
+
+fn main() {
+    #[cfg(feature = "redox")]
+    env_logger::init();
+
+    let mut daemonize = true;
+    let mut disk_path: Option<String> = None;
+    let mut mountpoint: Option<String> = None;
+
+    for arg in env::args().skip(1) {
+        match arg.as_str() {
+            "--no-daemon" | "-d" => daemonize = false,
+            _ if disk_path.is_none() => disk_path = Some(arg),
+            _ if mountpoint.is_none() => mountpoint = Some(arg),
+            _ => fail_usage("too many arguments provided"),
+        }
+    }
+
+    let Some(disk_path) = disk_path else {
+        fail_usage("no disk path provided");
+    };
+    let Some(mountpoint) = mountpoint else {
+        fail_usage("no mountpoint provided");
+    };
+
+    if daemonize {
+        let pipes = match make_pipe() {
+            Ok(pipes) => pipes,
+            Err(err) => {
+                eprintln!("fatd: failed to create pipe: {err}");
+                process::exit(1);
+            }
+        };
+
+        let mut read = unsafe { File::from_raw_fd(pipes[0] as RawFd) };
+        let write = unsafe { File::from_raw_fd(pipes[1] as RawFd) };
+
+        match fork_process() {
+            Ok(0) => {
+                drop(read);
+                process::exit(daemon(&disk_path, &mountpoint, Some(write)));
+            }
+            Ok(_pid) => {
+                drop(write);
+                let mut response = [1u8; 1];
+                if let Err(err) = read.read_exact(&mut response) {
+                    eprintln!("fatd: failed to read child status: {err}");
+                    process::exit(1);
+                }
+                process::exit(i32::from(response[0]));
+            }
+            Err(err) => {
+                eprintln!("fatd: failed to fork: {err}");
+                process::exit(1);
+            }
+        }
+    } else {
+        log::info!("running fatd in foreground");
+        process::exit(daemon(&disk_path, &mountpoint, None));
+    }
+}
@@ -0,0 +1,70 @@
+use std::io::{Read, Seek, Write};
+use std::sync::atomic::Ordering;
+
+use fscommon::BufStream;
+use redox_scheme::{
+    RequestKind, Response, SignalBehavior, Socket,
+    scheme::{SchemeState, SchemeSync, register_sync_scheme},
+};
+
+use crate::{IS_UMT, scheme::FatScheme};
+
+pub fn mount<D, T, F>(
+    filesystem: fatfs::FileSystem<BufStream<D>>,
+    mountpoint: &str,
+    callback: F,
+) -> syscall::error::Result<T>
+where
+    D: Read + Write + Seek,
+    F: FnOnce(&str) -> T,
+{
+    let socket = Socket::create()?;
+
+    let scheme_name = mountpoint.to_string();
+    let mounted_path = format!("/scheme/{mountpoint}");
+
+    let mut state = SchemeState::new();
+    let mut scheme = FatScheme::new(scheme_name, mounted_path.clone(), filesystem);
+
+    register_sync_scheme(&socket, mountpoint, &mut scheme)?;
+
+    let result = callback(&mounted_path);
+
+    while IS_UMT.load(Ordering::SeqCst) == 0 {
+        let request = match socket.next_request(SignalBehavior::Restart)? {
+            None => break,
+            Some(request) => match request.kind() {
+                RequestKind::Call(request) => request,
+                RequestKind::SendFd(sendfd_request) => {
+                    let response = Response::new(scheme.on_sendfd(&sendfd_request), sendfd_request);
+                    if !socket.write_response(response, SignalBehavior::Restart)? {
+                        break;
+                    }
+                    continue;
+                }
+                RequestKind::OnClose { id } => {
+                    scheme.on_close(id);
+                    state.on_close(id);
+                    continue;
+                }
+                RequestKind::OnDetach { id, pid } => {
+                    let Ok(inode) = scheme.inode(id) else {
+                        log::warn!("OnDetach received unknown handle id={id}");
+                        continue;
+                    };
+                    state.on_detach(id, inode, pid);
+                    continue;
+                }
+                _ => continue,
+            },
+        };
+
+        let response = request.handle_sync(&mut scheme, &mut state);
+        if !socket.write_response(response, SignalBehavior::Restart)? {
+            break;
+        }
+    }
+
+    scheme.cleanup()?;
+    Ok(result)
+}