---
title: "fd_fdstat_get()"
description: "The fd_fdstat_get() function is used to retrieve the metadata of a file descriptor. It provides information about the state of the file descriptor, such as its rights, flags, and file type."
url: "https://wasix.org/docs/api-reference/wasi/fd_fdstat_get/"
markdown: "https://wasix.org/docs/api-reference/wasi/fd_fdstat_get.md"
---

# `fd_fdstat_get()`

Get metadata of a file descriptor.

## Description

The `fd_fdstat_get()` function is used to retrieve the metadata of a file descriptor. It provides information about the state of the file descriptor, such as its rights, flags, and file type.

In POSIX systems, file descriptors are small, non-negative integers used to represent open files, sockets, or other I/O resources. They serve as handles that allow processes to read from or write to these resources. The `fd_fdstat_get()` function allows applications to retrieve information about a specific file descriptor, gaining insights into its properties and characteristics.

## Syntax

```ebnf
  ;;; Note: This returns similar flags to `fcntl(fd, F_GETFL)` in POSIX, as well as additional fields.
  ;;; Get the attributes of a file descriptor.
  (@interface func (export "fd_fdstat_get")
    (param $fd $fd)
    ;;; The buffer where the file descriptor's attributes are stored.
    (result $error (expected $fdstat (error $errno)))
  )
```

## Parameters

- `ctx`: A mutable reference to the function environment.
- `fd`: The file descriptor whose metadata will be accessed.
- `buf_ptr`: A WebAssembly pointer to a memory location where the metadata will be written.

## Return Value

The function returns an `Errno` value indicating the success or failure of the operation.

## POSIX Context

In POSIX-compliant systems, file descriptors are fundamental to I/O operations. They are obtained through various system calls such as `open()`, `socket()`, or `pipe()`. Each file descriptor maintains its own set of properties, including access rights, flags, and file type.

The `fd_fdstat_get()` function corresponds to the POSIX `fstat()` system call, which retrieves information about an open file descriptor. By invoking `fd_fdstat_get()`, applications can query the metadata associated with a file descriptor and access relevant details, such as the file’s mode, size, or ownership.

## Note

The `fd_fdstat_get()` function retrieves the metadata of the specified file descriptor. It writes the metadata to the provided memory location. This allows applications to examine the properties of a file descriptor and make informed decisions based on its characteristics.

---

[Documentation index](https://wasix.org/llms.txt) · [HTML version](https://wasix.org/docs/api-reference/wasi/fd_fdstat_get/)