feat(vfs): sparse writes with coverage-map cache (clean rewrite)

.github/workflows/ci.yml

@@ -121,6 +121,14 @@ jobs:
         timeout-minutes: 10
         run: cargo test --release --test fsx -- --test-threads=1 --nocapture
 
+      - name: fsx paranoid (CAS round-trip per mutation, --sparse-writes)
+        timeout-minutes: 15
+        run: cargo test --release --test fsx_paranoid -- --test-threads=1 --nocapture
+
+      - name: sparse concurrent real-CAS (multi-worker same-inode, --sparse-writes)
+        timeout-minutes: 15
+        run: cargo test --release --test sparse_concurrent_real -- --test-threads=1 --nocapture
+
   xfstests:
     name: xfstests (filesystem exerciser)
     runs-on:

Cargo.toml

@@ -10,10 +10,10 @@ categories = ["filesystem", "command-line-utilities"]
 
 [dependencies]
 # xet-core crates
-xet-client = { git = "https://github.com/huggingface/xet-core.git", branch = "main" }
-xet-core-structures = { git = "https://github.com/huggingface/xet-core.git", branch = "main" }
-xet-data = { git = "https://github.com/huggingface/xet-core.git", branch = "main" }
-xet-runtime = { git = "https://github.com/huggingface/xet-core.git", branch = "main" }
+xet-client = { git = "https://github.com/huggingface/xet-core.git", rev = "40f9530753e48f9517b5ad09e2339df7059d8de4" }
+xet-core-structures = { git = "https://github.com/huggingface/xet-core.git", rev = "40f9530753e48f9517b5ad09e2339df7059d8de4" }
+xet-data = { git = "https://github.com/huggingface/xet-core.git", rev = "40f9530753e48f9517b5ad09e2339df7059d8de4" }
+xet-runtime = { git = "https://github.com/huggingface/xet-core.git", rev = "40f9530753e48f9517b5ad09e2339df7059d8de4" }
 
 # External crates
 async-trait = "0.1"

src/nfs.rs

@@ -816,6 +816,15 @@ fn errno_to_nfs(e: i32) -> nfsstat3 {
         libc::ENOTEMPTY => nfsstat3::NFS3ERR_NOTEMPTY,
         libc::EBADF => nfsstat3::NFS3ERR_STALE,
         libc::ENOSPC => nfsstat3::NFS3ERR_NOSPC,
+        // EAGAIN is used internally as the sparse-write drift sentinel
+        // (`open_advanced_write` returns it when poll rotates xet_hash
+        // between snapshot and install). The internal retry loop in
+        // `open()` normally upgrades a final EAGAIN to EIO so userspace
+        // never sees it, but map it defensively here to NFS3ERR_JUKEBOX
+        // (the conventional retryable-busy code) so a future code path
+        // that leaks EAGAIN doesn't degrade to NFS3ERR_IO on an NFS
+        // export.
+        libc::EAGAIN => nfsstat3::NFS3ERR_JUKEBOX,
         _ => nfsstat3::NFS3ERR_IO,
     }
 }