refactor(userspace): split syscall/fat16/ext4 by concern; trim comments

crates/drivers/block/virtio/src/lib.rs

@@ -29,9 +29,8 @@ pub struct VirtioBlockDevice {
 }
 
 impl VirtioBlockDevice {
-    /// Takes over the block device whose MMIO region `mmio` names: maps
-    /// it, allocates the queue and request buffers, and resets the device
-    /// onto them. `None` if any step fails or it is not a block device.
+    /// Takes over the virtio block device behind `mmio`. `None` if it is
+    /// not one or any step fails.
     pub fn new(mmio: types::bounded::CapSlot) -> Option<Self> {
         libkos::device::map_mmio(mmio, MMIO_BASE).ok()?;
         let regs = UserMmio;