"no such device" when calling read()

Hi!

I just started learning v4l2. Im trying to write a small program which captures one frame and then terminates. The ioctl calls are all working, but when I call read() it fails, telling me that there is "no such device". Although I just used this very file descriptor to do the ioctl stuff. It is no I guess I'm missing something important. Any help is appreciated.

Im using a QuickCam for Notebooks (the current model). I already checked, that this cam supports the read() I/O. The output of the code beneath is:

---- output ------
Device sucessfuly opened.
read(): No such device
----------------------

---- code ------------------------------------------- int main()
{
int fd = open("/dev/video0",O_RDWR);

   if( fd == -1 ) {
       // error message here
   }
   else {
       cout << "Device sucessfuly opened." << endl;
   }

   // save one image and exit
   int mb = 1048576;
   char* buf = new char[mb]; // 1MB
   ssize_t bytesRead = read(fd, buf, mb);

   if (-1 == bytesRead ) {
       perror ("read()");
       exit (EXIT_FAILURE);

}
}
-------------------------------------------------------------

The file descriptor looks like this:
---------
crw-rw---- 1 root video 81, 0 2008-03-02 23:10 video0
---------

I am in the video group. I even ran the program as root.

cheers,
Janosch

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