feat(userspace): shell runs programs (ls, cat) via spawn w/ terminal+storage+args page; ext4 holes read as zeros; storage re-attach same buffer

crates/servers/storage-server/src/server.rs

@@ -23,6 +23,8 @@ pub trait Buffers {
 struct Client {
     badge: usize,
     buf: &'static mut [u8],
+    /// What maps `buf`, sent again when the same client attaches again.
+    cap: Option<CapSlot>,
 }
 
 pub struct StorageServer<F: FileSystem, B: Buffers> {
@@ -77,9 +79,11 @@ impl<F: FileSystem, B: Buffers> StorageServer<F, B> {
         self.clients.iter_mut().flatten().find(|c| c.badge == badge)
     }
 
+    /// A client attaching again gets its buffer again: the programs a shell
+    /// runs one after another share its badge.
     fn attach(&mut self, badge: usize) -> (StorageResponse, Option<CapSlot>) {
-        if self.client(badge).is_some() {
-            return (StorageResponse::Error, None);
+        if let Some(c) = self.client(badge) {
+            return (StorageResponse::Attached { size: c.buf.len() }, c.cap);
         }
         let Some(index) = self.clients.iter().position(Option::is_none) else {
             return (StorageResponse::Error, None);
@@ -89,7 +93,7 @@ impl<F: FileSystem, B: Buffers> StorageServer<F, B> {
         };
         let size = buf.len();
         if let Some(slot) = self.clients.get_mut(index) {
-            *slot = Some(Client { badge, buf });
+            *slot = Some(Client { badge, buf, cap });
         }
         (StorageResponse::Attached { size }, cap)
     }