chrubis@xxxxxxx writes:
> Hi!
> Looking carefully at the io_setup.2 man page it says:
>
> ...
> The io_setup() system call creates an asynchronous I/O context capable
> of concurrently processing at least nr_events.
> ...
> ^
> The 'at least' caught my eye, as it is it
> may suggest that the nr_events is low limit
> on the number of events.
>
>
> Wouldn't be 'at most' more appropriate here? Quick look in the kernel
> sources suggest that it allocates buffers for nr_events elements.
>
> Or am I missing something?
When the kernel ring buffer is setup, it is created in page size
chunks, and nr_events is rounded up:
/* Compensate for the ring buffer's head/tail overlap entry */
nr_events += 2; /* 1 is required, 2 for good luck */
size = sizeof(struct aio_ring);
size += sizeof(struct io_event) * nr_events;
nr_pages = (size + PAGE_SIZE-1) >> PAGE_SHIFT;
if (nr_pages < 0)
return -EINVAL;
nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring)) / sizeof(struct io_event);
Cheers,
Jeff
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