Limit the number of segments in single bio request

kernel/comps/block/src/bio.rs

@@ -136,6 +136,8 @@ pub enum BioEnqueueError {
     IsFull,
     /// Refuse to enqueue the bio
     Refused,
+    /// Too big bio
+    TooBig,
 }
 
 impl From<BioEnqueueError> for aster_frame::Error {

kernel/comps/block/src/lib.rs

@@ -55,6 +55,8 @@ pub const SECTOR_SIZE: usize = 512;
 pub trait BlockDevice: Send + Sync + Any + Debug {
     /// Enqueues a new `SubmittedBio` to the block device.
     fn enqueue(&self, bio: SubmittedBio) -> Result<(), BioEnqueueError>;
+    /// Returns the upper limit for the number of segments per bio.
+    fn max_nr_segments_per_bio(&self) -> usize;
 }
 
 impl dyn BlockDevice {

kernel/comps/block/src/request_queue.rs

@@ -20,18 +20,30 @@ pub struct BioRequestSingleQueue {
     queue: Mutex<VecDeque<BioRequest>>,
     num_requests: AtomicUsize,
     wait_queue: WaitQueue,
+    max_nr_segments_per_bio: usize,
 }
 
 impl BioRequestSingleQueue {
     /// Creates an empty queue.
     pub fn new() -> Self {
+        Self::with_max_nr_segments_per_bio(usize::MAX)
+    }
+
+    /// Creates an empty queue with the upper bound for the number of segments in a bio.
+    pub fn with_max_nr_segments_per_bio(max_nr_segments_per_bio: usize) -> Self {
         Self {
             queue: Mutex::new(VecDeque::new()),
             num_requests: AtomicUsize::new(0),
             wait_queue: WaitQueue::new(),
+            max_nr_segments_per_bio,
         }
     }
 
+    /// Returns the upper limit for the number of segments per bio.
+    pub fn max_nr_segments_per_bio(&self) -> usize {
+        self.max_nr_segments_per_bio
+    }
+
     /// Returns the number of requests currently in this queue.
     pub fn num_requests(&self) -> usize {
         self.num_requests.load(Ordering::Relaxed)
@@ -45,9 +57,15 @@ impl BioRequestSingleQueue {
     ///
     /// This method will wake up the waiter if a new `BioRequest` is enqueued.
     pub fn enqueue(&self, bio: SubmittedBio) -> Result<(), BioEnqueueError> {
+        if bio.segments().len() >= self.max_nr_segments_per_bio {
+            return Err(BioEnqueueError::TooBig);
+        }
+
         let mut queue = self.queue.lock();
         if let Some(request) = queue.front_mut() {
-            if request.can_merge(&bio) {
+            if request.can_merge(&bio)
+                && request.num_segments() + bio.segments().len() <= self.max_nr_segments_per_bio
+            {
                 request.merge_bio(bio);
                 return Ok(());
             }
@@ -123,6 +141,8 @@ pub struct BioRequest {
     type_: BioType,
     /// The range of target sectors on the device
     sid_range: Range<Sid>,
+    /// The number of segments
+    num_segments: usize,
     /// The submitted bios
     bios: VecDeque<SubmittedBio>,
 }
@@ -143,6 +163,11 @@ impl BioRequest {
         self.bios.iter()
     }
 
+    /// Returns the number of segments.
+    pub fn num_segments(&self) -> usize {
+        self.num_segments
+    }
+
     /// Returns `true` if can merge the `SubmittedBio`, `false` otherwise.
     pub fn can_merge(&self, rq_bio: &SubmittedBio) -> bool {
         if rq_bio.type_() != self.type_ {
@@ -163,6 +188,8 @@ impl BioRequest {
     pub fn merge_bio(&mut self, rq_bio: SubmittedBio) {
         assert!(self.can_merge(&rq_bio));
 
+        let rq_bio_nr_segments = rq_bio.segments().len();
+
         if rq_bio.sid_range().start == self.sid_range.end {
             self.sid_range.end = rq_bio.sid_range().end;
             self.bios.push_back(rq_bio);
@@ -170,6 +197,8 @@ impl BioRequest {
             self.sid_range.start = rq_bio.sid_range().start;
             self.bios.push_front(rq_bio);
         }
+
+        self.num_segments += rq_bio_nr_segments;
     }
 }
 
@@ -178,6 +207,7 @@ impl From<SubmittedBio> for BioRequest {
         Self {
             type_: bio.type_(),
             sid_range: bio.sid_range().clone(),
+            num_segments: bio.segments().len(),
             bios: {
                 let mut bios = VecDeque::with_capacity(1);
                 bios.push_front(bio);