feat(virtio-block): Add support for VIRTIO_BLK_T_DISCARD request type

src/vmm/src/devices/virtio/block/virtio/device.rs

@@ -25,7 +25,7 @@ use crate::devices::virtio::block::CacheType;
 use crate::devices::virtio::block::virtio::metrics::{BlockDeviceMetrics, BlockMetricsPerDevice};
 use crate::devices::virtio::device::{DeviceState, IrqTrigger, IrqType, VirtioDevice};
 use crate::devices::virtio::generated::virtio_blk::{
-    VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_RO, VIRTIO_BLK_ID_BYTES,
+    VIRTIO_BLK_F_FLUSH, VIRTIO_BLK_F_RO, VIRTIO_BLK_ID_BYTES, VIRTIO_BLK_F_DISCARD,
 };
 use crate::devices::virtio::generated::virtio_config::VIRTIO_F_VERSION_1;
 use crate::devices::virtio::generated::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
@@ -295,7 +295,8 @@ impl VirtioBlock {
             .map_err(VirtioBlockError::RateLimiter)?
             .unwrap_or_default();
 
-        let mut avail_features = (1u64 << VIRTIO_F_VERSION_1) | (1u64 << VIRTIO_RING_F_EVENT_IDX);
+        let mut avail_features = (1u64 << VIRTIO_F_VERSION_1) | (1u64 << VIRTIO_RING_F_EVENT_IDX)
+        | (1u64 << VIRTIO_BLK_F_DISCARD);
 
         if config.cache_type == CacheType::Writeback {
             avail_features |= 1u64 << VIRTIO_BLK_F_FLUSH;

src/vmm/src/devices/virtio/block/virtio/io/async_io.rs

@@ -110,7 +110,7 @@ impl AsyncFileEngine {
         Ok(())
     }
 
-    #[cfg(test)]
+
     pub fn file(&self) -> &File {
         &self.file
     }
@@ -230,6 +230,27 @@ impl AsyncFileEngine {
         Ok(())
     }
 
+    pub fn push_discard(
+        &mut self,
+        offset: u64,
+        len: u32,
+        req: PendingRequest,
+    ) -> Result<(), RequestError<AsyncIoError>> {
+        let wrapped_user_data = WrappedRequest::new(req);
+
+        self.ring
+            .push(Operation::fallocate(
+                0,
+                len,
+                offset,
+                wrapped_user_data,
+            ))
+            .map_err(|(io_uring_error, data)| RequestError {
+                req: data.req,
+                error: AsyncIoError::IoUring(io_uring_error),
+            })
+    }
+
     fn do_pop(&mut self) -> Result<Option<Cqe<WrappedRequest>>, AsyncIoError> {
         self.ring.pop().map_err(AsyncIoError::IoUring)
     }

src/vmm/src/devices/virtio/block/virtio/io/mod.rs

@@ -6,9 +6,12 @@ pub mod sync_io;
 
 use std::fmt::Debug;
 use std::fs::File;
+use libc::{c_int, off64_t, FALLOC_FL_KEEP_SIZE, FALLOC_FL_PUNCH_HOLE};
+use std::os::unix::io::AsRawFd;
 
 pub use self::async_io::{AsyncFileEngine, AsyncIoError};
 pub use self::sync_io::{SyncFileEngine, SyncIoError};
+use crate::device_manager::mmio::MMIO_LEN;
 use crate::devices::virtio::block::virtio::PendingRequest;
 use crate::devices::virtio::block::virtio::device::FileEngineType;
 use crate::vstate::memory::{GuestAddress, GuestMemoryMmap};
@@ -75,7 +78,7 @@ impl FileEngine {
         Ok(())
     }
 
-    #[cfg(test)]
+
     pub fn file(&self) -> &File {
         match self {
             FileEngine::Async(engine) => engine.file(),
@@ -172,6 +175,32 @@ impl FileEngine {
             FileEngine::Sync(engine) => engine.flush().map_err(BlockIoError::Sync),
         }
     }
+
+    pub fn discard(
+        &mut self,
+        offset: u64,
+        count: u32,
+        req: PendingRequest,
+    ) -> Result<FileEngineOk, RequestError<BlockIoError>> {
+
+        match self {
+            FileEngine::Async(engine) => match engine.push_discard(offset, count, req) {
+                Ok(_) => Ok(FileEngineOk::Submitted),
+                Err(err) => Err(RequestError {
+                    req: err.req,
+                    error: BlockIoError::Async(err.error),
+                }),
+            },
+            FileEngine::Sync(engine) => match engine.discard(offset,count) {
+                Ok(count) => Ok(FileEngineOk::Executed(RequestOk { req, count })),
+                Err(err) => Err(RequestError {
+                    req,
+                    error: BlockIoError::Sync(err),
+                }),
+            },
+        }
+    }
+
 }
 
 #[cfg(test)]

src/vmm/src/devices/virtio/block/virtio/io/sync_io.rs

@@ -3,6 +3,8 @@
 
 use std::fs::File;
 use std::io::{Seek, SeekFrom, Write};
+use libc::{c_int, off64_t, FALLOC_FL_KEEP_SIZE, FALLOC_FL_PUNCH_HOLE};
+use std::os::unix::io::AsRawFd;
 
 use vm_memory::{GuestMemoryError, ReadVolatile, WriteVolatile};
 
@@ -18,6 +20,8 @@ pub enum SyncIoError {
     SyncAll(std::io::Error),
     /// Transfer: {0}
     Transfer(GuestMemoryError),
+    /// Discard: {0}
+    Discard(std::io::Error)
 }
 
 #[derive(Debug)]
@@ -33,7 +37,7 @@ impl SyncFileEngine {
         SyncFileEngine { file }
     }
 
-    #[cfg(test)]
+
     pub fn file(&self) -> &File {
         &self.file
     }
@@ -81,4 +85,30 @@ impl SyncFileEngine {
         // Sync data out to physical media on host.
         self.file.sync_all().map_err(SyncIoError::SyncAll)
     }
+
+    pub fn discard(&mut self, offset: u64, len: u32) -> Result<u32, SyncIoError> {
+
+        unsafe {
+            let ret = libc::fallocate(
+                self.file.as_raw_fd(),
+                libc::FALLOC_FL_PUNCH_HOLE | libc::FALLOC_FL_KEEP_SIZE,
+                offset as i64,
+                len as i64,
+            );
+            if ret != 0 {
+                return Err(SyncIoError::Discard(std::io::Error::last_os_error()));
+            }
+        }
+        Ok(len)
+    }
+
+    pub fn fallocate(fd: c_int, mode: i32, offset: off64_t, len: off64_t) -> Result<(), std::io::Error> {
+        let ret: i32 = unsafe { libc::fallocate(fd, mode, offset, len) };
+        if ret == 0 {
+            Ok(())
+        } else {
+            Err(std::io::Error::last_os_error())
+        }
+    }
+
 }

src/vmm/src/devices/virtio/block/virtio/metrics.rs

@@ -157,6 +157,8 @@ pub struct BlockDeviceMetrics {
     pub invalid_reqs_count: SharedIncMetric,
     /// Number of flushes operation triggered on this block device.
     pub flush_count: SharedIncMetric,
+    /// Number of discard operation triggered on this block device.
+    pub discard_count: SharedIncMetric,
     /// Number of events triggered on the queue of this block device.
     pub queue_event_count: SharedIncMetric,
     /// Number of events ratelimiter-related.
@@ -210,6 +212,7 @@ impl BlockDeviceMetrics {
         self.invalid_reqs_count
             .add(other.invalid_reqs_count.fetch_diff());
         self.flush_count.add(other.flush_count.fetch_diff());
+        self.discard_count.add(other.discard_count.fetch_diff());
         self.queue_event_count
             .add(other.queue_event_count.fetch_diff());
         self.rate_limiter_event_count

src/vmm/src/devices/virtio/block/virtio/mod.rs

@@ -63,4 +63,12 @@ pub enum VirtioBlockError {
     RateLimiter(std::io::Error),
     /// Persistence error: {0}
     Persist(crate::devices::virtio::persist::PersistError),
+    /// Sector overflow in discard segment
+    SectorOverflow,
+    /// Discard segment exceeds disk size
+    BeyondDiskSize,
+    /// Invalid flags in discard segment
+    InvalidDiscardFlags,
+    /// Invalid discard request (e.g., empty segments)
+    InvalidDiscardRequest,
 }

src/vmm/src/devices/virtio/block/virtio/request.rs

@@ -9,17 +9,19 @@ use std::convert::From;
 
 use vm_memory::GuestMemoryError;
 
+use super::io::{BlockIoError, SyncIoError};
 use super::{SECTOR_SHIFT, SECTOR_SIZE, VirtioBlockError, io as block_io};
 use crate::devices::virtio::block::virtio::device::DiskProperties;
 use crate::devices::virtio::block::virtio::metrics::BlockDeviceMetrics;
 pub use crate::devices::virtio::generated::virtio_blk::{
     VIRTIO_BLK_ID_BYTES, VIRTIO_BLK_S_IOERR, VIRTIO_BLK_S_OK, VIRTIO_BLK_S_UNSUPP,
     VIRTIO_BLK_T_FLUSH, VIRTIO_BLK_T_GET_ID, VIRTIO_BLK_T_IN, VIRTIO_BLK_T_OUT,
+    VIRTIO_BLK_T_DISCARD
 };
 use crate::devices::virtio::queue::DescriptorChain;
 use crate::logger::{IncMetric, error};
 use crate::rate_limiter::{RateLimiter, TokenType};
-use crate::vstate::memory::{ByteValued, Bytes, GuestAddress, GuestMemoryMmap};
+use crate::vstate::memory::{ByteValued, Bytes, GuestAddress, GuestMemoryMmap, Address};
 
 #[derive(Debug, derive_more::From)]
 pub enum IoErr {
@@ -34,6 +36,7 @@ pub enum RequestType {
     Out,
     Flush,
     GetDeviceID,
+    Discard,
     Unsupported(u32),
 }
 
@@ -44,6 +47,7 @@ impl From<u32> for RequestType {
             VIRTIO_BLK_T_OUT => RequestType::Out,
             VIRTIO_BLK_T_FLUSH => RequestType::Flush,
             VIRTIO_BLK_T_GET_ID => RequestType::GetDeviceID,
+            VIRTIO_BLK_T_DISCARD => RequestType::Discard,
             t => RequestType::Unsupported(t),
         }
     }
@@ -176,6 +180,12 @@ impl PendingRequest {
             (Ok(transferred_data_len), RequestType::GetDeviceID) => {
                 Status::from_data(self.data_len, transferred_data_len, true)
             }
+            (Ok(_), RequestType::Discard) => {
+                block_metrics.discard_count.inc();
+                Status::Ok {
+                    num_bytes_to_mem: 0,
+                }
+            }
             (_, RequestType::Unsupported(op)) => Status::Unsupported { op },
             (Err(err), _) => Status::IoErr {
                 num_bytes_to_mem: 0,
@@ -231,13 +241,24 @@ impl RequestHeader {
     }
 }
 
+// For this, please see VirtIO v1.2. This struct mimics that of the implementation in Virtio.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[repr(C)]
+pub struct DiscardSegment {
+    sector: u64,
+    num_sectors: u32,
+    flags: u32,
+}
+unsafe impl ByteValued for DiscardSegment {}
+
 #[derive(Debug, PartialEq, Eq)]
 pub struct Request {
     pub r#type: RequestType,
     pub data_len: u32,
     pub status_addr: GuestAddress,
     sector: u64,
     data_addr: GuestAddress,
+    discard_segments: Option<Vec<DiscardSegment>>,
 }
 
 impl Request {
@@ -258,10 +279,11 @@ impl Request {
             data_addr: GuestAddress(0),
             data_len: 0,
             status_addr: GuestAddress(0),
+            discard_segments: None
         };
 
         let data_desc;
-        let status_desc;
+        let mut status_desc;
         let desc = avail_desc
             .next_descriptor()
             .ok_or(VirtioBlockError::DescriptorChainTooShort)?;
@@ -272,6 +294,7 @@ impl Request {
             if req.r#type != RequestType::Flush {
                 return Err(VirtioBlockError::DescriptorChainTooShort);
             }
+            data_desc = desc;
         } else {
             data_desc = desc;
             status_desc = data_desc
@@ -287,6 +310,9 @@ impl Request {
             if !data_desc.is_write_only() && req.r#type == RequestType::GetDeviceID {
                 return Err(VirtioBlockError::UnexpectedReadOnlyDescriptor);
             }
+            if data_desc.is_write_only() && req.r#type == RequestType::Discard {
+                return Err(VirtioBlockError::UnexpectedWriteOnlyDescriptor);
+            }
 
             req.data_addr = data_desc.addr;
             req.data_len = data_desc.len;
@@ -313,6 +339,45 @@ impl Request {
                     return Err(VirtioBlockError::InvalidDataLength);
                 }
             }
+            RequestType::Discard => {
+                // Validate data length
+                let segment_size = std::mem::size_of::<DiscardSegment>() as u32;
+                if data_desc.len % segment_size != 0 {
+                    return Err(VirtioBlockError::InvalidDataLength);
+                }
+
+                // Calculate number of segments
+                let num_segments = data_desc.len / segment_size;
+                if num_segments == 0 {
+                    return Err(VirtioBlockError::InvalidDiscardRequest);
+                }
+                let mut segments = Vec::with_capacity(num_segments as usize);
+
+                // Populate DiscardSegments vector
+                for i in 0..num_segments {
+                    let offset = i * segment_size;
+                    let segment: DiscardSegment = mem.read_obj(data_desc.addr.unchecked_add(offset as u64))
+                        .map_err(VirtioBlockError::GuestMemory)?;
+                    if segment.flags & !0x1 != 0 {
+                        return Err(VirtioBlockError::InvalidDiscardFlags);
+                    }
+                    let end_sector = segment.sector.checked_add(segment.num_sectors as u64)
+                        .ok_or(VirtioBlockError::SectorOverflow)?;
+                    if end_sector > num_disk_sectors {
+                        return Err(VirtioBlockError::BeyondDiskSize);
+                    }
+                    segments.push(segment);
+                }
+
+                // Assign to req.discard_segments
+                req.discard_segments = Some(segments);
+                req.data_len = data_desc.len;
+                status_desc = data_desc.next_descriptor()
+                    .ok_or(VirtioBlockError::DescriptorChainTooShort)?;
+                if !status_desc.is_write_only() {
+                    return Err(VirtioBlockError::UnexpectedReadOnlyDescriptor);
+                }
+            }
             _ => {}
         }
 
@@ -390,6 +455,11 @@ impl Request {
                     .map_err(IoErr::GetId);
                 return ProcessingResult::Executed(pending.finish(mem, res, block_metrics));
             }
+            RequestType::Discard => {
+                let _metric = block_metrics.write_agg.record_latency_metrics();
+                disk.file_engine
+                    .discard(self.offset(), self.data_len, pending)
+            }
             RequestType::Unsupported(_) => {
                 return ProcessingResult::Executed(pending.finish(mem, Ok(0), block_metrics));
             }
@@ -730,6 +800,7 @@ mod tests {
                 RequestType::Out => VIRTIO_BLK_T_OUT,
                 RequestType::Flush => VIRTIO_BLK_T_FLUSH,
                 RequestType::GetDeviceID => VIRTIO_BLK_T_GET_ID,
+                RequestType::Discard => VIRTIO_BLK_T_DISCARD,
                 RequestType::Unsupported(id) => id,
             }
         }
@@ -742,6 +813,7 @@ mod tests {
             RequestType::Out => VIRTQ_DESC_F_NEXT,
             RequestType::Flush => VIRTQ_DESC_F_NEXT,
             RequestType::GetDeviceID => VIRTQ_DESC_F_NEXT | VIRTQ_DESC_F_WRITE,
+            RequestType::Discard => VIRTQ_DESC_F_NEXT,
             RequestType::Unsupported(_) => VIRTQ_DESC_F_NEXT,
         }
     }
@@ -833,6 +905,7 @@ mod tests {
             status_addr,
             sector: sector & (NUM_DISK_SECTORS - sectors_len),
             data_addr,
+            discard_segments: None
         };
         let mut request_header = RequestHeader::new(virtio_request_id, request.sector);
 

src/vmm/src/io_uring/operation/mod.rs

@@ -29,6 +29,8 @@ pub enum OpCode {
     Write = generated::IORING_OP_WRITE as u8,
     /// Fsync operation.
     Fsync = generated::IORING_OP_FSYNC as u8,
+    /// Fallocate operation.
+    Fallocate = generated::IORING_OP_FALLOCATE as u8,
 }
 
 // Useful for outputting errors.
@@ -38,6 +40,7 @@ impl From<OpCode> for &'static str {
             OpCode::Read => "read",
             OpCode::Write => "write",
             OpCode::Fsync => "fsync",
+            OpCode::Fallocate => "fallocate",
         }
     }
 }
@@ -113,6 +116,19 @@ impl<T: Debug> Operation<T> {
         }
     }
 
+    /// Construct a fallocate operation.
+    pub fn fallocate(fd: FixedFd, len: u32, offset: u64, user_data: T) -> Self {
+        Self {
+            fd,
+            opcode: OpCode::Fallocate,
+            addr: None,
+            len: Some(len),
+            flags: 0,
+            offset: Some(offset),
+            user_data,
+        }
+    }
+
     pub(crate) fn fd(&self) -> FixedFd {
         self.fd
     }

tests/integration_tests/functional/test_discard.py

@@ -0,0 +1,38 @@
+import pytest
+import os
+import host_tools.drive as drive_tools
+
+
+def test_discard_support(uvm_plain_rw):
+    """
+    Test the VIRTIO_BLK_T_DISCARD feature for valid and invalid requests.
+    """
+
+    vm = uvm_plain_rw
+    vm.spawn()
+    vm.basic_config()
+    vm.add_net_iface()
+
+    fs1 = drive_tools.FilesystemFile(os.path.join(vm.fsfiles, "test_disk"), size=128)
+    vm.add_drive(
+        drive_id="test_disk",
+        path_on_host=fs1.path,
+        is_root_device=False,
+        is_read_only=False,
+    )
+
+    vm.start()
+
+    exit_code, stdout, _ = vm.ssh.run("cat /sys/block/vda/queue/discard_max_bytes")
+
+    assert exit_code == 0, "Failed to read discard_max_bytes"
+    assert int(stdout.strip()) > 0, f"discard_max_bytes is 0: {stdout}"
+
+    vm.ssh.run("mount -o remount,discard /")
+    exit_code, stdout, _ = vm.ssh.run("mount | grep /dev/vda")
+    assert exit_code == 0, f"Failed to remount root filesystem with discard option: {stdout}"
+
+    exit_code, stdout, _ = vm.ssh.run("fstrim -v /")
+    assert exit_code == 0, f"fstrim -v failed: {stdout}"
+    assert "bytes trimmed" in stdout, f"Unexpected fstrim output: {stdout}"
+    vm.kill()