How to get the device type associated with a fd

Question

Hi, i get a valid "fd" object from a caller. How can i find out what is the fd type - whether it is referring to a File, Socket, Device, etc? Depending on the refered type, i need to execute specific functions, say if the fd is associated with a File, then i need to do a read. If it is associated with a socket, then i need to get the socket properties.

Answer 1

Well, in theory at least, you still do a read for a socket, and for a device, and for a pipe, and.... :-P

If you want more data from the socket, such as the socket addresses, you can just call the functions for doing that. It will simply fail for non-sockets, and it's up to you to decide how you want to deal with that.

---

If you really must know, do an fstat on your file descriptor, then look at its mode (st_mode):

mode_t type;
struct stat fdstat;
/* ... */
if (fstat(fd, &fdstat) == -1)
    /* error out */
type = fdstat.st_mode & S_IFMT;
switch (type) {
case S_IFSOCK:
    /* socket */
case S_IFIFO:
    /* FIFO */
/* other cases */
}