vfs: implement file truncation, bump open file limit

kernel/libk/src/vfs/file/mod.rs

@@ -357,6 +357,17 @@ impl File {
         }
     }
 
+    /// Resizes this file to match the requested `size`
+    pub fn truncate(&self, size: u64) -> Result<(), Error> {
+        match &self.inner {
+            FileInner::Regular(file) => file.truncate(size),
+            _ => {
+                log::error!("TODO: truncate operation on unsupported file type");
+                Err(Error::InvalidOperation)
+            }
+        }
+    }
+
     /// Interprets the file as a poll channel
     pub fn as_poll_channel(&self) -> Result<&FdPoll, Error> {
         if let FileInner::Poll(poll) = &self.inner {
@@ -586,6 +597,8 @@ impl<T: TerminalHalf> TerminalHalfWrapper<T> {
 }
 
 impl FileSet {
+    const MAX_FILES: usize = 256;
+
     /// Creates an empty [FileSet]
     pub fn new() -> Self {
         Self {
@@ -610,7 +623,7 @@ impl FileSet {
     /// Associates a `file` with any available [RawFd] and returns it
     pub fn place_file(&mut self, file: FileRef, skip_stdio: bool) -> Result<RawFd, Error> {
         let start = if skip_stdio { 3 } else { 0 };
-        for idx in start..64 {
+        for idx in start..Self::MAX_FILES as u32 {
             let fd = RawFd::from(idx);
 
             if let Entry::Vacant(e) = self.map.entry(fd) {

kernel/libk/src/vfs/file/regular.rs

@@ -52,6 +52,14 @@ impl RegularFile {
         reg.write(&self.node, self.instance_data.as_ref(), pos, buf)
     }
 
+    pub fn truncate(&self, size: u64) -> Result<(), Error> {
+        if !self.write {
+            return Err(Error::InvalidFile);
+        }
+        let reg = self.node.as_regular()?;
+        reg.truncate(&self.node, size)
+    }
+
     // TODO should seek beyond the end of a read-only file be allowed?
     pub fn seek(&self, from: SeekFrom) -> Result<u64, Error> {
         let mut position = self.position.lock();

kernel/libk/src/vfs/node/ops.rs

@@ -269,11 +269,11 @@ impl Node {
         // Try to fetch the size from the cache
         let mut props = self.props.lock();
 
-        if let Some(size) = props.size {
-            return Ok(size);
-        }
-
         if self.flags.contains(NodeFlags::IN_MEMORY_SIZE) {
+            if let Some(size) = props.size {
+                return Ok(size);
+            }
+
             if let Ok(dir) = self.as_directory() {
                 return Ok(dir.children.lock().len() as _);
             }

kernel/src/syscall/imp/sys_io.rs

@@ -97,9 +97,10 @@ pub(crate) fn read(fd: RawFd, buffer: &mut [u8]) -> Result<usize, Error> {
 }
 
 pub(crate) fn truncate(fd: RawFd, size: u64) -> Result<(), Error> {
-    let _ = fd;
-    let _ = size;
-    todo!()
+    let thread = Thread::current();
+    let process = thread.process();
+
+    run_with_io(&process, |io| io.files.file(fd)?.truncate(size))
 }
 
 pub(crate) fn fsync(fd: RawFd, what: FileSync) -> Result<(), Error> {