Re: [Qemu-devel] [PATCH v2 1/2] vhost: add used memslot number for vhost-user and vhost-kernel separately

[Zhoujian (jay)]

> -----Original Message-----
> From: Igor Mammedov [mailto:address@hidden
> Sent: Thursday, December 28, 2017 7:12 PM
> To: Zhoujian (jay) <address@hidden>
> Cc: Huangweidong (C) <address@hidden>; address@hidden; wangxin
> (U) <address@hidden>; address@hidden; Liuzhe (Cloud Open
> Labs, NFV) <address@hidden>; address@hidden; Gonglei (Arei)
> <address@hidden>
> Subject: Re: [Qemu-devel] [PATCH v2 1/2] vhost: add used memslot number
> for vhost-user and vhost-kernel separately
> 
> On Sat, 23 Dec 2017 07:09:51 +0000
> "Zhoujian (jay)" <address@hidden> wrote:
> 
> > Hi Igor,
> >
> > > -----Original Message-----
> > > From: Igor Mammedov [mailto:address@hidden
> > > Sent: Saturday, December 23, 2017 3:03 AM
> > > To: Zhoujian (jay) <address@hidden>
> > > Cc: Huangweidong (C) <address@hidden>; address@hidden;
> > > wangxin
> > > (U) <address@hidden>; address@hidden; Liuzhe
> > > (Cloud Open Labs, NFV) <address@hidden>;
> > > address@hidden; Gonglei
> > > (Arei) <address@hidden>
> > > Subject: Re: [Qemu-devel] [PATCH v2 1/2] vhost: add used memslot
> > > number for vhost-user and vhost-kernel separately
> > >
> > > On Fri, 22 Dec 2017 17:25:13 +0100
> > > Igor Mammedov <address@hidden> wrote:
> > >
> > > > On Fri, 15 Dec 2017 16:45:54 +0800 Jay Zhou
> > > > <address@hidden> wrote:
> > > [...]
> > >
> > > > > +static void vhost_user_set_used_memslots(struct vhost_dev *dev) {
> > > > > +    int counter = 0;
> > > > > +    int i;
> > > > > +
> > > > > +    for (i = 0; i < dev->mem->nregions; ++i) {
> > > > > +        struct vhost_memory_region *reg = dev->mem->regions + i;
> > > > > +        ram_addr_t offset;
> > > > > +        MemoryRegion *mr;
> > > > > +        int fd;
> > > > > +
> > > > > +        assert((uintptr_t)reg->userspace_addr == reg-
> >userspace_addr);
> > > > > +        mr = memory_region_from_host((void *)(uintptr_t)reg-
> > > >userspace_addr,
> > > > > +                                    &offset);
> > > > > +        fd = memory_region_get_fd(mr);
> > > > > +        if (fd > 0) {
> > > > > +            counter++;
> > > > > +        }
> > > > > +    }
> > > > vhost_user_set_mem_table() already does the same counting, there
> > > > is no point in duplicating it, just drop vhost_set_used_memslots
> > > > callback
> > > >
> > > > > +    vhost_user_used_memslots = counter;
> > > > and update this value from vhost_user_set_mem_table()
> > > never mind, updating it from vhost_user_set_mem_table() as it's
> > > called only when device is started which is not the case when
> > > backend is initialized, so the way you did it should work for both
> > > cases
> > >
> >
> > How about do it like this(not sure whether the best way, any idea?):
> >
> > Define a new function, e.g.
> >
> > static void vhost_user_set_used_memslots_and_msgs(struct vhost_dev *dev,
> >                             VhostUserMsg *msg, size_t *fd_num, int
> > *fds)
> s/vhost_user_set_used_memslots_and_msgs/vhost_user_prepare_msg/

Ok

> 
> > {
> >     int num = 0;
> >     int i;
> >
> >     for (i = 0; i < dev->mem->nregions; ++i) {
> >         struct vhost_memory_region *reg = dev->mem->regions + i;
> >         ram_addr_t offset;
> >         MemoryRegion *mr;
> >         int fd;
> >
> >         assert((uintptr_t)reg->userspace_addr == reg->userspace_addr);
> >         mr = memory_region_from_host((void *)(uintptr_t)reg-
> >userspace_addr,
> >                                 &offset);
> >         fd = memory_region_get_fd(mr);
> >         if (fd > 0) {
> >             if (msg && fd_num && fds) {
> >                 msg->payload.memory.regions[num].userspace_addr
> >                                         = reg->userspace_addr;
> >                 msg->payload.memory.regions[num].memory_size
> >                                         = reg->memory_size;
> >                 msg->payload.memory.regions[num].guest_phys_addr
> >                                         = reg->guest_phys_addr;
> >                 msg->payload.memory.regions[num].mmap_offset = offset;
> >                 assert(num < VHOST_MEMORY_MAX_NREGIONS);
> there is no need to assert here function can return error.

Ok

> 
> >                 fds[num++] = fd;
> Is num counting in wrong place?
> 
>    if (msg && fd_num && fds) => false
> is the case vhost_user_set_used_memslots(), so it won't count 'num'
> which is later used to intialize vhost_user_used_memslots.

My bad, will fix.

> >             }
> >         }
> >     }
> >     vhost_user_used_memslots = num;
> add comment here as it won't be obvious to reader why
> vhost_user_used_memslots is here

Will do.

> 
> >     if (fd_num)
> >         *fd_num = num;
> msg.payload.memory.nregions can be used directly instead of num amd fd_num
> and it's 1 less argument to pass out of function.
> 
> > }
> >
> > And call it when the backend is initialized and the device is started
> > respectively,
> >
> > static void vhost_user_set_used_memslots(struct vhost_dev *dev)
> static int
> 
> for return value
> 
> > {
> >     vhost_user_set_used_memslots_and_msgs(dev, NULL, NULL, NULL);
> we can do here
>         vhost_user_set_used_memslots_and_msgs(dev, &msg, &fd_num, fds);
> and discard/ignore results, that way it will be less conditionals inside
> of called function
> 
> > }
> >
> > static int vhost_user_set_mem_table(struct vhost_dev *dev,
> >                                             struct vhost_memory *mem)
> > {
> >     [...]
> >
> >     vhost_user_set_used_memslots_and_msgs(dev, &msg, &fd_num, fds);
>    rc = vhost_user_set_used_memslots_and_msgs(dev, &msg, &fd_num, fds);
> 
> and return error from vhost_user_set_mem_table(), caller should be able to
> coupe with error.
> 

Will fix all of them in the next version.

Regards,
Jay