style: replace errors for fallocate/discard with error logs

- added safety comments + minor error handling.
Signed-off-by: LDagnachew <leulmdagnachew@gmail.com>

Author: LDagnachew

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

@@ -110,6 +110,7 @@ impl AsyncFileEngine {
         Ok(())
     }
 
+    #[cfg(test)]
     pub fn file(&self) -> &File {
         &self.file
     }
@@ -237,12 +238,18 @@ impl AsyncFileEngine {
     ) -> 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),
-            })
+        if let Err((io_uring_error, data)) =
+            self.ring
+                .push(Operation::fallocate(0, len, offset, wrapped_user_data))
+        {
+            error!(
+                "DISCARD fallocate failed (offset={}, len={}): {:?}",
+                offset, len, io_uring_error
+            );
+            return Ok(());
+        }
+
+        Ok(())
     }
 
     fn do_pop(&mut self) -> Result<Option<Cqe<WrappedRequest>>, AsyncIoError> {

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

@@ -79,6 +79,7 @@ impl FileEngine {
         Ok(())
     }
 
+    #[cfg(test)]
     pub fn file(&self) -> &File {
         match self {
             FileEngine::Async(engine) => engine.file(),

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

@@ -37,6 +37,7 @@ impl SyncFileEngine {
         SyncFileEngine { file }
     }
 
+    #[cfg(test)]
     pub fn file(&self) -> &File {
         &self.file
     }
@@ -96,7 +97,7 @@ impl SyncFileEngine {
 
         let len_i64: i64 = len.into();
 
-        // SAFETY: calling libc::fallocate is safe here because:
+        // # Safety: calling libc::fallocate is safe here because:
         // - `self.file.as_raw_fd()` is a valid file descriptor owned by this struct,
         // - `off_i64` and `len_i64` are validated copies of the incoming unsigned values converted
         //   to the C `off64_t` type, and
@@ -109,25 +110,15 @@ impl SyncFileEngine {
                 len_i64,
             );
             if ret != 0 {
-                return Err(SyncIoError::Discard(std::io::Error::last_os_error()));
+                error!(
+                    "DISCARD fallocate failed (offset={}, len={}): {:?}",
+                    offset,
+                    len,
+                    std::io::Error::last_os_error()
+                );
+                return Ok(len);
             }
         }
         Ok(len)
     }
-
-    pub fn fallocate(
-        fd: c_int,
-        mode: i32,
-        offset: off64_t,
-        len: off64_t,
-    ) -> Result<(), std::io::Error> {
-        // SAFETY: calling libc::fallocate is safe because we're passing plain C-compatible
-        // integer types (fd, mode, offset, len) and we check the integer return value.
-        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/request.rs

@@ -361,15 +361,14 @@ impl Request {
                     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)?;
+                    let end_sector = segment.sector + segment.num_sectors as u64;
                     if end_sector > num_disk_sectors {
-                        return Err(VirtioBlockError::BeyondDiskSize);
+                        error!(
+                            "Discard request out of bounds: sector={} num_sectors={} \
+                             end_sector={} disk_sectors={}",
+                            segment.sector, segment.num_sectors, end_sector, num_disk_sectors
+                        );
+                        continue;
                     }
                     segments.push(segment);
                 }