Re: [PATCH] UserfaultFD: Rename uffd_api.bits into .features

[Pavel Emelyanov <xemul@parallels.com>]

On 05/07/2015 05:33 PM, Andrea Arcangeli wrote:
> On Thu, May 07, 2015 at 05:28:46PM +0300, Pavel Emelyanov wrote:
>> Yup, this is very close to what I did in my set -- introduced a message to
>> report back to the user-space on read. But my message is more than 8+2*1 bytes,
>> so we'll have one message for 0xAA API and another one for 0xAB (new) one :)
> 
> I slightly altered it to fix an issue with packet alignments so it'd
> be 16bytes.
> 
> How big is your msg currently? Could we get to use the same API?

Right now it's like this

struct uffd_event {
        __u64 type;
        union {
                struct {
                        __u64 addr;
                } pagefault;

                struct {
                        __u32 ufd;
                } fork;

                struct {
                        __u64 from;
                        __u64 to;
                        __u64 len;
                } remap;
        } arg;
};

where .type is your uffd_msg.event and the rest is event-specific.

> UFFDIO_REGISTER_MODE_FORK
> 
> or 
> 
> UFFDIO_REGISTER_MODE_NON_COOPERATIVE would differentiate if you want
> to register for fork/mremap/dontneed events as well or only the
> default (UFFD_EVENT_PAGEFAULT).

I planned to use this in UFFDIO_API call -- the uffdio_api.features will
be in-out argument denoting the bits user needs and reporting what kernel
can.

-- Pavel

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