Re: [PR] feat(ovfs): add filesystem to handle message [opendal]

["zjregee (via GitHub)" <gi...@apache.org>]

zjregee commented on code in PR #4720:
URL: https://github.com/apache/opendal/pull/4720#discussion_r1649565554


##########
integrations/virtiofs/src/filesystem.rs:
##########
@@ -0,0 +1,129 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use std::io::Write;
+use std::mem::size_of;
+
+use vm_memory::ByteValued;
+
+use crate::error::*;
+use crate::filesystem_message::*;
+use crate::virtiofs_util::{Reader, Writer};
+
+/// Version number of this interface.
+const KERNEL_VERSION: u32 = 7;
+/// Minor version number of this interface.
+const KERNEL_MINOR_VERSION: u32 = 38;
+/// Minimum Minor version number supported.
+const MIN_KERNEL_MINOR_VERSION: u32 = 27;
+/// The length of the header part of the message.
+const BUFFER_HEADER_SIZE: u32 = 256;
+/// The maximum length of the data part of the message, used for read/write data.
+const MAX_BUFFER_SIZE: u32 = 1 << 20;
+
+/// Filesystem is a filesystem implementation with opendal backend,
+/// and will decode and process messages from VMs.
+pub struct Filesystem {}
+
+#[allow(dead_code)]
+impl Filesystem {
+    pub fn new() -> Filesystem {
+        Filesystem {}
+    }
+
+    pub fn handle_message(&self, mut r: Reader, w: Writer) -> Result<usize> {
+        let in_header: InHeader = r
+            .read_obj()
+            .map_err(|e| new_vhost_user_fs_error("", Some(e.into())))?;
+        if in_header.len > (MAX_BUFFER_SIZE + BUFFER_HEADER_SIZE) {
+            // The message is too long here.
+            return reply_error(in_header.unique, w);
+        }
+        if let Ok(opcode) = Opcode::try_from(in_header.opcode) {
+            match opcode {
+                Opcode::Init => self.init(in_header, r, w),
+            }
+        } else {
+            reply_error(in_header.unique, w)
+        }
+    }
+
+    fn init(&self, in_header: InHeader, mut r: Reader, w: Writer) -> Result<usize> {
+        let InitIn { major, minor, .. } = r.read_obj().map_err(|e| {
+            new_vhost_user_fs_error("failed to decode protocol messages", Some(e.into()))
+        })?;
+
+        if major != KERNEL_VERSION || minor < MIN_KERNEL_MINOR_VERSION {
+            return reply_error(in_header.unique, w);
+        }
+
+        // We will directly return ok and do nothing for now.
+        let out = InitOut {
+            major: KERNEL_VERSION,
+            minor: KERNEL_MINOR_VERSION,
+            max_write: MAX_BUFFER_SIZE,
+            ..Default::default()
+        };
+        reply_ok(Some(out), None, in_header.unique, w)
+    }
+}
+
+fn reply_ok<T: ByteValued>(
+    out: Option<T>,
+    data: Option<&[u8]>,
+    unique: u64,
+    mut w: Writer,

Review Comment:
   It seems unnecessary. If I add a function called write_objs to the writer, I still need to encapsulate a reply_ok in the filesystem. If I move reply_ok directly to the writer, it will introduce certain semantics that the writer does not need to be aware of.
   
   I now put both methods reply_ok reply_error inside the filesystem.



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