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
     }

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

@@ -6,6 +6,8 @@ pub mod sync_io;
 
 use std::fmt::Debug;
 use std::fs::File;
+use libc::{c_int, off64_t};
+use std::os::unix::io::AsRawFd;
 
 pub use self::async_io::{AsyncFileEngine, AsyncIoError};
 pub use self::sync_io::{SyncFileEngine, SyncIoError};
@@ -33,6 +35,13 @@ pub enum BlockIoError {
     Async(AsyncIoError),
 }
 
+bitflags::bitflags! {
+    pub struct FallocateFlags: c_int {
+        const FALLOC_FL_KEEP_SIZE = 0x01;
+        const FALLOC_FL_PUNCH_HOLE = 0x02;
+    }
+}
+
 impl BlockIoError {
     pub fn is_throttling_err(&self) -> bool {
         match self {
@@ -75,7 +84,7 @@ impl FileEngine {
         Ok(())
     }
 
-    #[cfg(test)]
+
     pub fn file(&self) -> &File {
         match self {
             FileEngine::Async(engine) => engine.file(),
@@ -172,6 +181,34 @@ impl FileEngine {
             FileEngine::Sync(engine) => engine.flush().map_err(BlockIoError::Sync),
         }
     }
+
+    pub fn handle_discard(&self, offset: u64, len: u32) -> Result<(), std::io::Error> {
+        let fd = self.file().as_raw_fd();
+        let result = Self::fallocate(
+            fd,
+            FallocateFlags::FALLOC_FL_PUNCH_HOLE | FallocateFlags::FALLOC_FL_KEEP_SIZE,
+            offset as i64,
+            len as i64,
+        );
+        if let Err(e) = result {
+            eprintln!("Discard failed: {}", e);
+            return Err(std::io::Error::last_os_error());
+        }
+        Ok(())
+    }
+
+    pub fn fallocate(fd: c_int, mode: FallocateFlags, offset: off64_t, len: off64_t) -> Result<(), std::io::Error> {
+        // need to refer to libc library.
+        let ret: i32 = unsafe { libc::fallocate64(fd, mode.bits(), offset, len) };
+        if ret == 0 {
+            Ok(())
+        } else {
+            Err(std::io::Error::last_os_error())
+        }
+    }
+
+
+
 }
 
 #[cfg(test)]

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

@@ -18,6 +18,8 @@ pub enum SyncIoError {
     SyncAll(std::io::Error),
     /// Transfer: {0}
     Transfer(GuestMemoryError),
+    /// Discard: {0}
+    Discard(std::io::Error)
 }
 
 #[derive(Debug)]
@@ -33,7 +35,7 @@ impl SyncFileEngine {
         SyncFileEngine { file }
     }
 
-    #[cfg(test)]
+
     pub fn file(&self) -> &File {
         &self.file
     }

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 +241,23 @@ impl RequestHeader {
     }
 }
 
+// For this, please see VirtIO v1.2. This struct mimics that of the implementation in Virtio.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+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>>, // New field, holds ranges
 }
 
 impl Request {
@@ -258,10 +278,11 @@ 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)?;
@@ -313,6 +334,52 @@ impl Request {
                     return Err(VirtioBlockError::InvalidDataLength);
                 }
             }
+            RequestType::Discard => {
+                // Get data descriptor
+                let data_desc = avail_desc.next_descriptor()
+                    .ok_or(VirtioBlockError::DescriptorChainTooShort)?;
+                if data_desc.is_write_only() {
+                    return Err(VirtioBlockError::UnexpectedWriteOnlyDescriptor);
+                }
+
+                // Validate data length
+                let segment_size = std::mem::size_of::<DiscardSegment>() as u32; // 16 bytes
+                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 +457,22 @@ impl Request {
                     .map_err(IoErr::GetId);
                 return ProcessingResult::Executed(pending.finish(mem, res, block_metrics));
             }
+            RequestType::Discard => {
+                let res = disk
+                    .file_engine
+                    .handle_discard(self.offset(), self.data_len);
+
+                match res {
+                    Ok(()) => Ok(block_io::FileEngineOk::Executed(block_io::RequestOk {
+                        req: pending,
+                        count: 0,
+                    })),
+                    Err(e) => Err(block_io::RequestError {
+                        req: pending,
+                        error: BlockIoError::Sync(SyncIoError::Discard(e)),
+                    }),
+                }
+            }
             RequestType::Unsupported(_) => {
                 return ProcessingResult::Executed(pending.finish(mem, Ok(0), block_metrics));
             }
@@ -730,6 +813,7 @@ 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 +826,7 @@ 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 +918,7 @@ 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);