Re: opening things without the O_LARGEFILE flag


xhoster@xxxxxxxxx wrote:
"Athanasios" <aduitsis@xxxxxxxxx> wrote:
Hi everyone,

I am trying to open the /dev/net/tun character device with perl.

In C, I would issue:

open("/dev/net/tun", O_RDWR)

and continue as usual.

However, when I try to use sysopen in perl like

sysopen(TUNNELDEV, "/dev/net/tun", O_RDWR);

from the strace (truss) output I can see that instead it tries to do:

open("/dev/net/tun", O_RDWR|O_LARGEFILE)

which for some VERY strange reason succeeds but the file descriptor is
left in a bad state, so it is really unusable. For anything I try to do
afterwards, I get a

EBADFD (File descriptor in bad state).

As I have come down to the systel call level, there is no other reason
for this problem that I can think of except the O_LARGEFILE flag.
Indeed, a simple C program works quite fine without that flag.

Just to make sure it is absolutely nailed down, does the simple C program
stop working fine if you add the O_LARGEFILE in?

I 'll confirm that shortly, I haven't tried it yet. But judging from
the system calls I see in truss, it almost surely won't work.



I also have tried to use POSIX::open but it still adds the flag.

The documentation clearly states that from perl 5.6 and forth, the
O_LARGEFILE will be used whenever possible. But I really need to bypass
this and generate an open system call without it.

Maybe you could compile perl without large file support?

Or write a small C server that will accept socket connections and
proxy /dev/net/tun over the socket.

Yes, these are valid options, as is the Inline::C idea which the
previous poster suggested. But the general idea is that there *should*
be a way to omit the O_LARGEFILE flag if needed.

Kind Regards,
Athanasios


Xho

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