On Wed, 22 Nov 2006 11:45:52 +0100, Paolo Abeni <[EMAIL PROTECTED]> wrote:
BTW, I'm putting the cc: back. See, Marcel already replied. We ought
to keep people in the loop. Although generally others are interested
in patches only, it's good to have a record of the design process.
> One possible solution is to add another ioctl operation to remove a
> specified number of records (header+data) from the buffer. User use this
> ioctl after processing at least one urb.
Right, this is what I was going to do. It's part of what I call
"mfetch". The mfetch takes this struct:
struct mfetch_info {
unsigned int *offvec; /* Vector of events fetched */
int nfetch; /* Number of events to fetch (out: fetched) */
int nflush; /* Number of events to flush */
}
The ioctl works likes this:
- Drop up to nflush events
- Wait if !O_NONBLOCK and buffer is empty
- Extract up to nfetch offsets, stores them in offvec, returns how
many were fetched in nfetch.
The idea here is that polling without any syscalls is a no-goal,
considering systemic overhead elsewhere. By getting a bunch of
mmap offsets, applications use a "fraction of syscall per event"
model and do not need to think about wrapped buffers (they see
the filler packets, but it's a very small overhead).
I'm thinking if I should add a "force O_NONBLOCK" flag somehow,
in case someone wants to flush all events. If you find an application
which can make an intelligent use of it, please let me know.
I am going to write some test code and validate if this works.
> /*
> * remove args events or fillers from buffer. If args is
> greater
> * than the number of events present in buffer, fail
> * with error and no modification is applied to the buffer;
> */
> if (rp->cnt == 0) {
> rp->b_cnt = cnt;
> rp->b_out = out;
> ret = -EINVAL;
> break;
Why is that? I thought that it may be useful to start with INT_MAX
events to flush.
> BTW I tried to implement the MON_IOCT_RING_SIZE ioctl operation:
Yeah, I'll take that too, modulo sizes always being unsigned here
unless they are ssize_t (we have one case).
-- Pete
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