>>> On Sun, May 13, 2007 at 9:00 AM, in message <[EMAIL PROTECTED]>,
Avi Kivity <[EMAIL PROTECTED]> wrote:
> Gregory Haskins wrote:
>> Signed- off- by: Gregory Haskins <[EMAIL PROTECTED]>
>>
>
> Please include patch descriptions.
Ack.
On that topic: Does anyone know how to retroactively change the patch comment
in StGIT?
>
>> ---
>>
>> drivers/kvm/kvm.h | 2 +
>> drivers/kvm/kvm_main.c | 82
> ++++++++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 84 insertions(+), 0 deletions(- )
>>
>> diff -- git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
>> index 7b5d5e6..1c46830 100644
>> --- a/drivers/kvm/kvm.h
>> +++ b/drivers/kvm/kvm.h
>> @@ - 333,6 +333,8 @@ struct kvm_vcpu_irq {
>> int deferred;
>> struct task_struct *task;
>> int guest_mode;
>> + wait_queue_head_t wq;
>> + int usignal;
>> };
>>
>> struct kvm_vcpu {
>> diff -- git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
>> index 3304cce..9a6d2c5 100644
>> --- a/drivers/kvm/kvm_main.c
>> +++ b/drivers/kvm/kvm_main.c
>> @@ - 40,6 +40,7 @@
>> #include <linux/file.h>
>> #include <linux/fs.h>
>> #include <linux/mount.h>
>> +#include <linux/poll.h>
>>
>> #include "x86_emulate.h"
>> #include "segment_descriptor.h"
>> @@ - 326,6 +327,7 @@ static struct kvm *kvm_create_vm(void)
>> memset(&vcpu- >irq, 0, sizeof(vcpu- >irq));
>> spin_lock_init(&vcpu- >irq.lock);
>> vcpu- >irq.deferred = - 1;
>> + init_waitqueue_head(&vcpu- >irq.wq);
>>
>> vcpu- >cpu = - 1;
>> vcpu- >kvm = kvm;
>> @@ - 2288,11 +2290,78 @@ static int kvm_vcpu_release(struct inode *inode,
> struct file *filp)
>> return 0;
>> }
>>
>> +static unsigned int kvm_vcpu_poll(struct file *filp, poll_table *wait)
>> +{
>> + struct kvm_vcpu *vcpu = filp- >private_data;
>> + unsigned int events = 0;
>> + unsigned long flags;
>> +
>> + poll_wait(filp, &vcpu- >irq.wq, wait);
>> +
>> + spin_lock_irqsave(&vcpu- >irq.lock, flags);
>> + if (vcpu- >irq.usignal)
>> + events |= POLLIN;
>> + spin_unlock_irqrestore(&vcpu- >irq.lock, flags);
>> +
>> + return events;
>> +}
>> +
>> +static ssize_t kvm_vcpu_read(struct file *filp, char __user *buf, size_t
> count,
>> + loff_t *ppos)
>> +{
>>
>
> Is having a read() (or a write()) actually necessary?
Based on what I know: yes. It could be a case of ignorance, however ;)
Heres why I think its necessary: You need poll to simply tell you when
something is pending. You can't clear the pending status in poll because you
cannot predict the internal access pattern (e.g. I assume it could be polled
multiple times by the kernel without returning immediately to userspace).
Therefore, you need a second method to actually clear the pending "signal",
which I use the read() method for. I can be convinced otherwise, but that was
my original thinking.
>
>> +
>> + if (indirect_sig && waitqueue_active(&vcpu- >irq.wq))
>> + wake_up(&vcpu- >irq.wq);
>> }
>>
>>
>
> Did you check that we can actually deliver signals with this? I think a
> fasync_struct or something like that is necessary, but not sure.
Actually, my signals *didn't* seem to be working, but they werent working with
"send_sig()" either so I just assumed I had a userspace coding problem. Based
on what I read, it seemed like what I did should work if you do a
fcntl(F_SETSIG), etc. But again, it could be ignorance. I am not familiar
with fasync_struct. If you have any pointers, please forward.
>
> Another implementation option (which I've only thought of now, sorry) is
> to have an ioctl which returns a real eventfd, reducing some code
> duplication.
So based on this, I assume eventfd must be in the kernel already? Cool. Even
if its not, I like this idea much better than what I did. There was still an
unresolved problem regarding how I was going to expose the signaling mechanism
to QEMU without giving away the vcpu_fd from the kvmctl library that this
solves nicely.
With this methodology, I can simply provide a function like
"kvm_vcpu_get_eventfd()" in the library, and return the eventfd directly to the
QEMU process. Then we dont have to worry about layering violations. Nice!
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