fix: amplify io is too large to hold in fuse buffer

Fuse request buffer is fixed by `FUSE_KERN_BUF_SIZE * pagesize() + FUSE_HEADER_ SIZE`. When amplify io is larger than it, FuseDevWriter suffers from smaller buffer. As a result, invalid data error is returned.

Reproduction:
    run nydusd with 3MB amplify_io
    error from random io:
        reply error header OutHeader { len: 16, error: -5, unique: 108 }, error Custom { kind: InvalidData, error: "data out of range, available 1052656 requested 1250066" }

Details:
    size of fuse buffer = 1052656 + 16 (size of inner header) = 256(page number) * 4096(page size) + 4096(fuse header)
    let amplify_io = min(user_specified, fuseWriter.available_bytes())

Resolution:
    This pr is not best implements, but independent of modification to [fuse-backend-rs]("https://github.com/cloud-hypervisor/fuse-backend-rs").
    In future, evalucation of amplify_io will be replaced with [ZeroCopyWriter.available_bytes()]("cloud-hypervisor/fuse-backend-rs#135").

Signed-off-by: 泰友 <[email protected]>

Cargo.toml

@@ -35,7 +35,7 @@ path = "src/lib.rs"
 anyhow = "1"
 clap = { version = "4.0.18", features = ["derive", "cargo"] }
 flexi_logger = { version = "0.25", features = ["compress"] }
-fuse-backend-rs = "^0.10.3"
+fuse-backend-rs = "^0.10.4"
 hex = "0.4.3"
 hyper = "0.14.11"
 hyperlocal = "0.8.0"

rafs/src/fs.rs

@@ -621,19 +621,20 @@ impl FileSystem for Rafs {
         assert!(!io_vecs.is_empty() && !io_vecs[0].is_empty());
 
         // Try to amplify user io for Rafs v5, to improve performance.
-        if self.sb.meta.is_v5() && size < self.amplify_io {
+        let amplify_io = cmp::min(self.amplify_io as usize, w.available_bytes()) as u32;
+        if self.sb.meta.is_v5() && size < amplify_io {
             let all_chunks_ready = self.device.all_chunks_ready(&io_vecs);
             if !all_chunks_ready {
                 let chunk_mask = self.metadata().chunk_size as u64 - 1;
                 let next_chunk_base = (offset + (size as u64) + chunk_mask) & !chunk_mask;
                 let window_base = cmp::min(next_chunk_base, inode_size);
                 let actual_size = window_base - (offset & !chunk_mask);
-                if actual_size < self.amplify_io as u64 {
-                    let window_size = self.amplify_io as u64 - actual_size;
-                    let orig_cnt = io_vecs.iter().fold(0, |s, d| s + d.len());
+                if actual_size < amplify_io as u64 {
+                    let window_size = amplify_io as u64 - actual_size;
+                    let orig_cnt = descs.iter().fold(0, |s, d| s + d.len());
                     self.sb.amplify_io(
                         &self.device,
-                        self.amplify_io,
+                        amplify_io,
                         &mut io_vecs,
                         &inode,
                         window_base,