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SubjectRE: How to notify a user process from within a driver
On Thu, 1 May 2003, Lee, Shuyu wrote:

> Richard and Alan,
> Thank you for the info. Given the prototype for poll() is
> "int poll(struct pollfd *ufds, unsigned int nfds, int timeout);", and pollfd
> is struct pollfd {int fd; short events; short revents};, how do I
> communicate complex info to the driver?
> For example, assuming there are 8 input lines on my hardware, and the user
> wants to be notified in the following three cases:
> 1) input on Line 1 only,
> 2) input on either Line 2 or Line 3,
> 3) input on both Line 4 and Line 5,
> how do I pass that info to the driver? Also, other than POLLERR and POLLHUP,
> can I pass back to the user more descriptive error messages?
> Thanks,
> Shuyu

poll() tells you something happened, ioctl() tells you what. Poll
has some bits (POLLIN, POLLOUT, etc.) that can be used to tell
the user-mode task what information to actually request in the
ioctl() call. Your ioctl() can receive and send anything if you
use the third variable as a pointer to your stuff.

struct info {
int a;
int b;
} info;
int fd;
struct pollfd pfd;
fd = open("/dev/device", O_RDWR);

pfd.fd = fd; = POLLIN;
pfd.revents = 0;
if(poll(&pfd, 1, 0) <= 0)
else if (pfd.revents & POLLIN)
ret = ioctl(fd, GET_MY_INFORMATION, &foo);
else if (pfd.revents & POLLOUT)
ret = ioctl(fd, CHANGE_CONFIGURATION, &how);

Dick Johnson
Penguin : Linux version 2.4.20 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.

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