disks: Add loopback device support and load associated disk

Signed-off-by: Ikey Doherty <[email protected]>

crates/disks/src/lib.rs

@@ -3,9 +3,13 @@
 // SPDX-License-Identifier: MPL-2.0
 
 mod disk;
-use std::{fs, io, path::PathBuf};
+use std::{
+    fs, io,
+    path::{Path, PathBuf},
+};
 
 pub use disk::*;
+pub mod loopback;
 pub mod mmc;
 pub mod nvme;
 pub mod partition;
@@ -20,7 +24,7 @@ const DEVFS_DIR: &str = "/dev";
 pub enum BlockDevice {
     /// A physical disk device
     Disk(Box<Disk>),
-    Unknown,
+    Loopback(Box<loopback::Device>),
 }
 
 impl BlockDevice {
@@ -33,6 +37,22 @@ impl BlockDevice {
         Self::discover_in_sysroot("/")
     }
 
+    /// Returns the name of the block device.
+    pub fn name(&self) -> &str {
+        match self {
+            BlockDevice::Disk(disk) => disk.name(),
+            BlockDevice::Loopback(device) => device.name(),
+        }
+    }
+
+    /// Returns the path to the block device in /dev.
+    pub fn device(&self) -> &Path {
+        match self {
+            BlockDevice::Disk(disk) => disk.device_path(),
+            BlockDevice::Loopback(device) => device.device_path(),
+        }
+    }
+
     /// Discovers block devices in a specified sysroot directory.
     ///
     /// # Arguments
@@ -48,24 +68,28 @@ impl BlockDevice {
         let mut devices = Vec::new();
 
         // Iterate over all block devices in sysfs and collect their filenames
-        let entries = fs::read_dir(&sysfs_dir)?
+        let mut entries = fs::read_dir(&sysfs_dir)?
             .filter_map(Result::ok)
-            .filter_map(|e| Some(e.file_name().to_str()?.to_owned()));
+            .filter_map(|e| Some(e.file_name().to_str()?.to_owned()))
+            .collect::<Vec<_>>();
+        entries.sort();
 
         // For all the discovered block devices, try to create a Disk instance
         // At this point we completely ignore partitions. They come later.
         for entry in entries {
-            let disk = if let Some(disk) = scsi::Disk::from_sysfs_path(&sysfs_dir, &entry) {
-                Disk::Scsi(disk)
+            let device = if let Some(disk) = scsi::Disk::from_sysfs_path(&sysfs_dir, &entry) {
+                BlockDevice::Disk(Box::new(Disk::Scsi(disk)))
             } else if let Some(disk) = nvme::Disk::from_sysfs_path(&sysfs_dir, &entry) {
-                Disk::Nvme(disk)
+                BlockDevice::Disk(Box::new(Disk::Nvme(disk)))
             } else if let Some(disk) = mmc::Disk::from_sysfs_path(&sysfs_dir, &entry) {
-                Disk::Mmc(disk)
+                BlockDevice::Disk(Box::new(Disk::Mmc(disk)))
+            } else if let Some(device) = loopback::Device::from_sysfs_path(&sysfs_dir, &entry) {
+                BlockDevice::Loopback(Box::new(device))
             } else {
                 continue;
             };
 
-            devices.push(BlockDevice::Disk(Box::new(disk)));
+            devices.push(device);
         }
 
         Ok(devices)
@@ -80,10 +104,27 @@ mod tests {
     fn test_discover() {
         let devices = BlockDevice::discover().unwrap();
         for device in &devices {
-            if let BlockDevice::Disk(disk) = device {
-                println!("{}: {disk}", disk.name());
-                for partition in disk.partitions() {
-                    println!("├─{} {partition}", partition.name);
+            match device {
+                BlockDevice::Disk(disk) => {
+                    println!("{}: {disk}", disk.name());
+                    for partition in disk.partitions() {
+                        println!("├─{} {partition}", partition.name);
+                    }
+                }
+                BlockDevice::Loopback(device) => {
+                    if let Some(file) = device.file_path() {
+                        if let Some(disk) = device.disk() {
+                            println!("Loopback device: {} (backing file: {})", device.name(), file.display());
+                            println!("└─Disk: {} ({})", disk.name(), disk.model().unwrap_or("Unknown"));
+                            for partition in disk.partitions() {
+                                println!("  ├─{} {partition}", partition.name);
+                            }
+                        } else {
+                            println!("Loopback device: {} (backing file: {})", device.name(), file.display());
+                        }
+                    } else {
+                        println!("Loopback device: {}", device.name());
+                    }
                 }
             }
         }

crates/disks/src/loopback.rs

@@ -0,0 +1,79 @@
+// SPDX-FileCopyrightText: Copyright © 2025 Serpent OS Developers
+//
+// SPDX-License-Identifier: MPL-2.0
+
+//! Loopback device enumeration and handling.
+//!
+//! Loopback devices in Linux are block devices that map files to block devices.
+//! This module handles enumeration and management of these devices,
+//! which appear as `/dev/loop*` block devices.
+
+use std::path::{Path, PathBuf};
+
+use crate::{sysfs, BasicDisk, DiskInit, DEVFS_DIR, SYSFS_DIR};
+
+/// Represents a loop device.
+#[derive(Debug)]
+pub struct Device {
+    /// The device name (e.g. "loop0", "loop1")
+    name: String,
+
+    /// Path to the device in /dev
+    device: PathBuf,
+
+    /// Optional backing file path
+    file: Option<PathBuf>,
+
+    /// Optional disk device if the loop device is backed by a disk
+    disk: Option<BasicDisk>,
+}
+
+impl Device {
+    /// Creates a new Device instance from a sysfs path if the device name matches loop device pattern.
+    ///
+    /// # Arguments
+    ///
+    /// * `sysroot` - The root path of the sysfs filesystem
+    /// * `name` - The device name to check (e.g. "loop0", "loop1")
+    ///
+    /// # Returns
+    ///
+    /// * `Some(Device)` if the name matches loop pattern (starts with "loop" followed by numbers)
+    /// * `None` if the name doesn't match or the device can't be initialized
+    pub(crate) fn from_sysfs_path(sysroot: &Path, name: &str) -> Option<Self> {
+        let matching = name.starts_with("loop") && name[4..].chars().all(char::is_numeric);
+        let node = sysroot.join(SYSFS_DIR).join(name);
+        let file = sysfs::read::<PathBuf>(sysroot, &node, "loop/backing_file");
+        let disk = file.as_ref().and_then(|_| BasicDisk::from_sysfs_path(sysroot, name));
+        if matching {
+            Some(Self {
+                name: name.to_owned(),
+                device: PathBuf::from(DEVFS_DIR).join(name),
+                file,
+                disk,
+            })
+        } else {
+            None
+        }
+    }
+
+    /// Returns the device name.
+    pub fn name(&self) -> &str {
+        &self.name
+    }
+
+    /// Returns the device path.
+    pub fn device_path(&self) -> &Path {
+        &self.device
+    }
+
+    /// Returns the backing file path.
+    pub fn file_path(&self) -> Option<&Path> {
+        self.file.as_deref()
+    }
+
+    /// Returns the disk device if the loop device is backed by a disk.
+    pub fn disk(&self) -> Option<&BasicDisk> {
+        self.disk.as_ref()
+    }
+}