On Sat, 19 May 2007 21:07:11 -0300 Davi Arnaut <[EMAIL PROTECTED]> wrote:
> Hi,
>
> Gathering signals in bulk enables server applications to drain a signal
> queue (almost full of realtime signals) more efficiently by reducing the
> syscall and file look-up overhead.
>
> Very similar to the sigtimedwait4() call described by Niels Provos,
> Chuck Lever, and Stephen Tweedie in a paper entitled "Analyzing the
> Overload Behavior of a Simple Web Server". The paper lists more details
> and advantages.
>
static ssize_t signalfd_read(struct file *file, char __user *buf, size_t count,
loff_t *ppos)
{
struct signalfd_ctx *ctx = file->private_data;
struct signalfd_siginfo __user *siginfo;
int nonblock = file->f_flags & O_NONBLOCK;
ssize_t ret, total = 0;
siginfo_t info;
count /= sizeof(struct signalfd_siginfo);
if (!count)
return -EINVAL;
siginfo = (struct signalfd_siginfo __user *) buf;
do {
ret = signalfd_dequeue(ctx, &info, nonblock);
if (unlikely(ret <= 0))
break;
ret = signalfd_copyinfo(siginfo, &info);
if (ret < 0)
break;
siginfo++;
total += ret;
nonblock = 1;
} while (--count);
return total ? total : ret;
}
If 'count' is not a multiple of sizeof(struct signalfd_siginfo)), the read()
will return the next smallest multiple of `count'.
That is, unless `count' happens to be less than 1*sizeof(struct
signalfd_siginfo)), in which case we return -EINVAL.
This seems inconsistent.
Also, I'm desperately hunting for the place where we zero out that local
siginfo_t, and I ain't finding it. Someone please convince me that we're
not leaking bits of kernel memory out to userspace in that thing.
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