Does any1 know how to use sendfile() (in C) ?

[raul_]

Why doesn't this work??



...
n = sendfile(socket_fd,file_fd, NULL, 255);




[raul@horus myserver]$ ./myclient nexus.rnl 40000
Trying to connect
Connected to server
ERROR writing to socket: Bad file descriptor


I can use read and write, but I wanted to use sendfile for cleaner code :(

[gradedcheese]

Ah, in Linux that won't work. From "man sendfile":



Presently (Linux 2.6.9): in_fd, must correspond to a file which sup‐
ports mmap(2)-like operations (i.e., it cannot be a socket); and out_fd
must refer to a socket.

Applications may wish to fall back to read(2)/write(2) in the case
where sendfile() fails with EINVAL or ENOSYS.


My guess: sendfile() does everything inside the kernel, which in this case isn't very secure, while read/write make userspace->kernel trips each time, so they don't allow it. But I'm not sure.

EDIT: hmm, but the order of arguments is:



ssize_t sendfile(int out_fd, int in_fd, off_t *offset, size_t count);


so then as I understand it, that should work? What return value do you get?

[raul_]

Sorry for the late response, i've been away. It just returns -1. The error message is the one on the original post.

I'm just using normal read and write, but with sendfile i wouldn't have to create a buffer with a limited size and do several readings. I think...

[gradedcheese]

Well, for what it's worth, -1 is generally:



#define EPERM 1 /* Operation not permitted */


...so, just a guess: try running your test code with 'sudo'? What port are you using to communicate over?

[raul_]

It's not a permission problem =\ i'm using 40000 but that's just arbitrary. I guess i'll stick to the standard write and read procedures.

When I get sendfile working i'll post it here :)

[rejuvenate]

i am new to socket programming and need to build a ftp server how to recieve file at the client if i use sendfile().
thnx in advance

[Sinkingships7]

i am new to socket programming and need to build a ftp server how to recieve file at the client if i use sendfile().
thnx in advance

Welcome to the wooorld of tomorrooooww!

This post is over two years old, so you'll probably want to start a new thread. Although I commend you greatly for using the search feature so efficiently. =]