Re: [Bluez-devel] select(2) or read(2) on bluetooth sockets not working correctly?

[Marcel Holtmann <marcel@holtmann.org>]

Hi Pawel,

> In gnokii project, we use Bluetooth sockets as one of the phone
> communication medium. We use it in quite usual way (simplified code):
> 
> fd = socket(PF_BLUETOOTH, SOCK_STREAM, BTPROTO_RFCOMM);
> [...]
> bind(fd, (struct sockaddr *)&laddr, sizeof(laddr));
> [...]
> connect(fd, (struct sockaddr *)&raddr, sizeof(raddr));
> 
> Then we have (simplified code again):
> 
> while (1) {
>    [...]
>    write(fd, write_buf, size);
>    [...]
>    FD_ZERO(&readfds);
>    FD_SET(fd, &readfds);
>    if (select(fd + 1, &readfds, NULL, NULL, &timeout) > 0) {
>       read(fd, read_buf, size);
>       [...]
>    }
>    [...]
> }
> 
> The problem is (or rather was) that then bluetooth device gets out of
> range (or bluetooth gets disabled in the device) the program hangs on
> read(2). So select(2) went OK and told us that there's something to be
> read, but actually nothing can be read. According to select(2) manual
> page, after the successful select(2), read(2) should not hang (it may
> fail though).
> 
> It can be workarounded by setting O_NONBLOCK flag on the socket, but
> still I consider it as a bug that read(2) hangs after successful
> select(2).

which kernel version? Can you construct a simple demo program that shows
this effect easily with a 2.6.24-rc2 kernel?

Regards

Marcel



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