From ef54b1da6e972b4c102a488d2d5c93d5acb89512 Mon Sep 17 00:00:00 2001
From: Project516 <138796702+Project516@users.noreply.github.com>
Date: Wed, 4 Nov 2026 16:45:04 -0600
Subject: [PATCH 1/2] Report a file system's block size and space from the
 host, so direct I/O and FileStore work as on HotSpot

---
 src/fs.ts                 | 16 ++++++++++++++++
 src/natives/io.ts         |  8 +++++++-
 src/natives/nio.ts        | 14 ++++++++++++--
 src/node.ts               |  8 ++++++++
 test/java/FileStores.java | 20 ++++++++++++++++++++
 test/jtreg/passing.txt    |  4 ++++
 6 files changed, 67 insertions(+), 3 deletions(-)
 create mode 100644 test/java/FileStores.java

diff --git a/src/fs.ts b/src/fs.ts
index 9f65408..e5211ea 100644
--- a/src/fs.ts
+++ b/src/fs.ts
@@ -1,5 +1,12 @@
 // Virtual file system the Java side sees. Paths are absolute and use "/".
 
+export interface Space {
+  bsize: bigint;
+  blocks: bigint;
+  bfree: bigint;
+  bavail: bigint;
+}
+
 export interface Stat {
   dir: boolean;
   size: number;
@@ -30,6 +37,8 @@ export interface Backend {
   mkdir?(path: string): boolean;
   remove?(path: string): boolean;
   rename?(from: string, to: string): boolean;
+  // the file system holding path: block size and block counts, as statvfs gives them
+  space?(path: string): Space | null;
   // sets the modification time, in milliseconds since the epoch
   setMtime?(path: string, ms: number): boolean;
   // whether the host refuses to write the file, or to create it when it is missing
@@ -184,6 +193,13 @@ export class VFS {
     return !!r && r[0].writable;
   }
 
+  // A file system without its own figures reports 4 KB blocks and no space,
+  // as Linux does for virtual file systems such as /proc.
+  space(path: string): Space {
+    const r = this.resolve(path);
+    return (r && r[0].space?.(r[1])) ?? { bsize: 4096n, blocks: 0n, bfree: 0n, bavail: 0n };
+  }
+
   setMtime(path: string, ms: number): boolean {
     const r = this.resolve(path);
     return !!r && r[0].writable && !!r[0].setMtime?.(r[1], ms);
diff --git a/src/natives/io.ts b/src/natives/io.ts
index 170ee2a..5f10865 100644
--- a/src/natives/io.ts
+++ b/src/natives/io.ts
@@ -479,6 +479,12 @@ export const natives: Natives = {
     renamePath(t, resolvePath(t, pathOf(t, a)), resolvePath(t, pathOf(t, b))),
   [`${UFS}.setLastModifiedTime0(Ljava/io/File;J)Z`]: (t, [, f, ms]) => setMtime(t, resolvePath(t, pathOf(t, f)), Number(ms)),
   [`${UFS}.setReadOnly0(Ljava/io/File;)Z`]: (t, [, f]) => chmod(t, f, (m) => m & ~0o222),
-  [`${UFS}.getSpace0(Ljava/io/File;I)J`]: () => 0n,
+  // SPACE_TOTAL, SPACE_FREE or SPACE_USABLE of the file system holding f; 0 if f is missing
+  [`${UFS}.getSpace0(Ljava/io/File;I)J`]: (t, [, f, kind]) => {
+    const abs = resolvePath(t, pathOf(t, f));
+    if (!t.vm.fs.stat(abs)) return 0n;
+    const s = t.vm.fs.space(abs);
+    return s.bsize * (kind === 0 ? s.blocks : kind === 1 ? s.bfree : s.bavail);
+  },
   [`${UFS}.getNameMax0(Ljava/lang/String;)J`]: () => 255n,
 };
diff --git a/src/natives/nio.ts b/src/natives/nio.ts
index 929f1a9..aa2a350 100644
--- a/src/natives/nio.ts
+++ b/src/natives/nio.ts
@@ -241,7 +241,15 @@ export const natives: Natives = {
   [`${N}getpwnam0(J)I`]: () => 1000,
   [`${N}getgrnam0(J)I`]: () => 1000,
   [`${N}fchmodatNoFollowSupported0()Z`]: () => 0,
-  [`${N}statvfs0(JLsun/nio/fs/UnixFileStoreAttributes;)V`]: () => undefined,
+  [`${N}statvfs0(JLsun/nio/fs/UnixFileStoreAttributes;)V`]: (t, [p, attrs]) => {
+    const abs = path(t, p);
+    if (!t.vm.fs.stat(abs)) unixError(ENOENT);
+    const s = t.vm.fs.space(abs), A = "sun/nio/fs/UnixFileStoreAttributes";
+    t.vm.setField(attrs, A, "f_frsize", s.bsize);
+    t.vm.setField(attrs, A, "f_blocks", s.blocks);
+    t.vm.setField(attrs, A, "f_bfree", s.bfree);
+    t.vm.setField(attrs, A, "f_bavail", s.bavail);
+  },
   [`${N}flistxattr(IJI)I`]: () => 0,
   [`${N}getlinelen(J)I`]: () => -1,
   [`${N}rewind(J)V`]: () => undefined,
@@ -435,7 +443,9 @@ Object.assign(natives, {
   "java/nio/MappedMemoryUtils.isLoaded0(JJJ)Z": () => 1,
   "java/nio/MappedMemoryUtils.load0(JJ)V": () => undefined,
   "java/nio/MappedMemoryUtils.unload0(JJ)V": () => undefined,
-  [`${UFD}setDirect0(Ljava/io/FileDescriptor;)I`]: () => -1,
+  // Bytes go through the same buffers either way; this only reports the block
+  // size direct I/O aligns to, as fstatvfs gives it.
+  [`${UFD}setDirect0(Ljava/io/FileDescriptor;)I`]: (t, [fd]) => Number(t.vm.fs.space(chanFile(t, fd).path).bsize),
   "sun/nio/ch/FileDispatcherImpl.init0()V": () => undefined,
   "sun/nio/ch/FileDispatcherImpl.transferTo0(Ljava/io/FileDescriptor;JJLjava/io/FileDescriptor;Z)J": () => BigInt(UNSUPPORTED_CASE),
   "sun/nio/ch/FileDispatcherImpl.transferFrom0(Ljava/io/FileDescriptor;Ljava/io/FileDescriptor;JJZ)J": () => BigInt(UNSUPPORTED_CASE),
diff --git a/src/node.ts b/src/node.ts
index c523f8e..eef27ef 100644
--- a/src/node.ts
+++ b/src/node.ts
@@ -147,6 +147,14 @@ export class NodeBackend implements Backend {
       return false;
     }
   }
+  space(p: string) {
+    try {
+      const s = fs.statfsSync(this.host(p), { bigint: true });
+      return { bsize: s.bsize, blocks: s.blocks, bfree: s.bfree, bavail: s.bavail };
+    } catch {
+      return null;
+    }
+  }
   setMtime(p: string, ms: number) {
     try {
       fs.utimesSync(this.host(p), fs.statSync(this.host(p)).atime, ms / 1000);
diff --git a/test/java/FileStores.java b/test/java/FileStores.java
new file mode 100644
index 0000000..e714654
--- /dev/null
+++ b/test/java/FileStores.java
@@ -0,0 +1,20 @@
+import java.io.File;
+import java.nio.ByteBuffer;
+import java.nio.file.*;
+
+// A file store reports its host file system's block size and totals, as
+// statvfs gives them; direct I/O sizes its buffers from the block size.
+public class FileStores {
+  public static void main(String[] args) throws Exception {
+    Path tmp = Path.of(System.getProperty("java.io.tmpdir"));
+    FileStore store = Files.getFileStore(tmp);
+    long block = store.getBlockSize();
+    System.out.println("block size " + block);
+    System.out.println("total positive " + (store.getTotalSpace() > 0));
+    System.out.println("File total matches " + (tmp.toFile().getTotalSpace() == store.getTotalSpace()));
+    System.out.println("usable within total " + (store.getUsableSpace() <= store.getTotalSpace()));
+    System.out.println("missing file " + new File(tmp.toFile(), "no-such-file").getTotalSpace());
+    ByteBuffer buf = ByteBuffer.allocateDirect((int) block * 2).alignedSlice((int) block);
+    System.out.println("aligned capacity " + buf.capacity());
+  }
+}
diff --git a/test/jtreg/passing.txt b/test/jtreg/passing.txt
index d35c862..bf09c63 100644
--- a/test/jtreg/passing.txt
+++ b/test/jtreg/passing.txt
@@ -1979,6 +1979,10 @@ java/nio/channels/FileChannel/Truncate.java
 java/nio/channels/FileChannel/TruncateRAF.java
 java/nio/channels/FileChannel/TryLock.java
 java/nio/channels/FileChannel/Write.java
+java/nio/channels/FileChannel/directio/PreadDirect.java
+java/nio/channels/FileChannel/directio/PwriteDirect.java
+java/nio/channels/FileChannel/directio/ReadDirect.java
+java/nio/channels/FileChannel/directio/WriteDirect.java
 java/nio/channels/FileLock/FileLockConstructor.java
 java/nio/channels/FileLock/FileLockGC.java
 java/nio/channels/FileLock/Overlaps.java

From 179548051c7a32a5fbb67405c527dc7ab34e4172 Mon Sep 17 00:00:00 2001
From: Project516 <138796702+Project516@users.noreply.github.com>
Date: Wed, 4 Nov 2026 18:20:02 -0600
Subject: [PATCH 2/2] Take an unlinked file's block size from the path it had

---
 src/natives/nio.ts | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/natives/nio.ts b/src/natives/nio.ts
index 0f8c5bf..f359835 100644
--- a/src/natives/nio.ts
+++ b/src/natives/nio.ts
@@ -451,7 +451,11 @@ Object.assign(natives, {
   "java/nio/MappedMemoryUtils.unload0(JJ)V": () => undefined,
   // Bytes go through the same buffers either way; this only reports the block
   // size direct I/O aligns to, as fstatvfs gives it.
-  [`${UFD}setDirect0(Ljava/io/FileDescriptor;)I`]: (t, [fd]) => Number(t.vm.fs.space(chanFile(t, fd).path).bsize),
+  [`${UFD}setDirect0(Ljava/io/FileDescriptor;)I`]: (t, [fd]) => {
+    const f = chanFile(t, fd);
+    // an unlinked file has no path; the one it had names its file system
+    return Number(t.vm.fs.space(f.path || f.detached?.path || "/").bsize);
+  },
   "sun/nio/ch/FileDispatcherImpl.init0()V": () => undefined,
   "sun/nio/ch/FileDispatcherImpl.transferTo0(Ljava/io/FileDescriptor;JJLjava/io/FileDescriptor;Z)J": () => BigInt(UNSUPPORTED_CASE),
   "sun/nio/ch/FileDispatcherImpl.transferFrom0(Ljava/io/FileDescriptor;Ljava/io/FileDescriptor;JJZ)J": () => BigInt(UNSUPPORTED_CASE),