Auto merge of #1353 - divergentdave:file-set-len, r=RalfJung

Implement ftruncate64/ftruncate for File::set_len

This adds a shim for `ftruncate64` (on Linux) or `ftruncate` (on macOS) to enable support for `File::set_len`, and includes a test.

Author: bors

src/shims/foreign_items/posix/linux.rs

@@ -34,6 +34,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let result = this.linux_readdir64_r(args[0], args[1], args[2])?;
                 this.write_scalar(Scalar::from_i32(result), dest)?;
             }
+            "ftruncate64" => {
+                let result = this.ftruncate64(args[0], args[1])?;
+                this.write_scalar(Scalar::from_i32(result), dest)?;
+            }
             // Linux-only
             "posix_fadvise" => {
                 let _fd = this.read_scalar(args[0])?.to_i32()?;

src/shims/foreign_items/posix/macos.rs

@@ -44,6 +44,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let result = this.macos_readdir_r(args[0], args[1], args[2])?;
                 this.write_scalar(Scalar::from_i32(result), dest)?;
             }
+            "ftruncate" => {
+                let result = this.ftruncate64(args[0], args[1])?;
+                this.write_scalar(Scalar::from_i32(result), dest)?;
+            }
 
             // Environment related shims
             "_NSGetEnviron" => {

src/shims/fs.rs

@@ -1062,6 +1062,37 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             this.handle_not_found()
         }
     }
+
+    fn ftruncate64(
+        &mut self, fd_op: OpTy<'tcx, Tag>,
+        length_op: OpTy<'tcx, Tag>,
+    ) -> InterpResult<'tcx, i32> {
+        let this = self.eval_context_mut();
+
+        this.check_no_isolation("ftruncate64")?;
+
+        let fd = this.read_scalar(fd_op)?.to_i32()?;
+        let length = this.read_scalar(length_op)?.to_i64()?;
+        if let Some(FileHandle { file, writable }) = this.machine.file_handler.handles.get_mut(&fd) {
+            if *writable {
+                if let Ok(length) = length.try_into() {
+                    let result = file.set_len(length);
+                    this.try_unwrap_io_result(result.map(|_| 0i32))
+                } else {
+                    let einval = this.eval_libc("EINVAL")?;
+                    this.set_last_error(einval)?;
+                    Ok(-1)
+                }
+            } else {
+                // The file is not writable
+                let einval = this.eval_libc("EINVAL")?;
+                this.set_last_error(einval)?;
+                Ok(-1)
+            }
+        } else {
+            this.handle_not_found()
+        }
+    }
 }
 
 /// Extracts the number of seconds and nanoseconds elapsed between `time` and the unix epoch when

tests/run-pass/fs.rs

@@ -13,6 +13,7 @@ fn main() {
     test_file_create_new();
     test_seek();
     test_metadata();
+    test_file_set_len();
     test_symlink();
     test_errors();
     test_rename();
@@ -155,6 +156,32 @@ fn test_metadata() {
     remove_file(&path).unwrap();
 }
 
+fn test_file_set_len() {
+    let bytes = b"Hello, World!\n";
+    let path = prepare_with_content("miri_test_fs_set_len.txt", bytes);
+
+    // Test extending the file
+    let mut file = OpenOptions::new().read(true).write(true).open(&path).unwrap();
+    let bytes_extended = b"Hello, World!\n\x00\x00\x00\x00\x00\x00";
+    file.set_len(20).unwrap();
+    let mut contents = Vec::new();
+    file.read_to_end(&mut contents).unwrap();
+    assert_eq!(bytes_extended, contents.as_slice());
+
+    // Test truncating the file
+    file.seek(SeekFrom::Start(0)).unwrap();
+    file.set_len(10).unwrap();
+    let mut contents = Vec::new();
+    file.read_to_end(&mut contents).unwrap();
+    assert_eq!(&bytes[..10], contents.as_slice());
+
+    // Can't use set_len on a file not opened for writing
+    let file = OpenOptions::new().read(true).open(&path).unwrap();
+    assert_eq!(ErrorKind::InvalidInput, file.set_len(14).unwrap_err().kind());
+
+    remove_file(&path).unwrap();
+}
+
 fn test_symlink() {
     let bytes = b"Hello, World!\n";
     let path = prepare_with_content("miri_test_fs_link_target.txt", bytes);