Get metadata of a file descriptor.


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.


  ;;; 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)))


  • 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.


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.