[dpdk-dev] [PATCH v2 1/6] vhost: handle VHOST_USER_SET_LOG_BASE request

[Yuanhan Liu]

On Tue, Dec 22, 2015 at 02:41:43AM +0000, Xie, Huawei wrote:
> 
> 
> > -----Original Message-----
> > From: Yuanhan Liu [mailto:yuanhan.liu at linux.intel.com]
> > Sent: Tuesday, December 22, 2015 10:26 AM
> > To: Xie, Huawei
> > Cc: dev at dpdk.org; Michael S. Tsirkin; Victor Kaplansky; Iremonger,
> > Bernard; Pavel Fedin; Peter Xu
> > Subject: Re: [PATCH v2 1/6] vhost: handle VHOST_USER_SET_LOG_BASE
> > request
> > 
> > On Mon, Dec 21, 2015 at 03:32:53PM +0000, Xie, Huawei wrote:
> > > > +
> > > > +	/*
> > > > +	 * mmap from 0 to workaround a hugepage mmap bug: mmap will be
> > > > +	 * failed when offset is not page size aligned.
> > > > +	 */
> > > s /will be failed/will fail/
> > > mmap will fail when offset is not zero.
> I mistake for 4KB page size.

Didn't follow you.

> Please check if huge page size align is enough.

It should be. However, I don't think we need bother to do that:
first of all, it happened on few specific old kernels. And, "off"
here is kind of guaranteed to be 0. Last, even it's not, mmaping
it from 0 will resolve that.

> > > Also we only know this workaround is for hugetlbfs. Not sure of
> > other
> > > tmpfs, so mention hugetlbfs here.
> > 
> > I have already mentioned "to workaround a __hugepage__ mmap bug"; it's
> > not enough?
> Yes.
> > 
> > > > +	addr = mmap(0, size + off, PROT_READ | PROT_WRITE, MAP_SHARED, fd,
> > 0);
> > > > +	if (addr == MAP_FAILED) {
> > > > +		RTE_LOG(ERR, VHOST_CONFIG, "mmap log base failed!\n");
> > > > +		return -1;
> > > > +	}
> > > > +
> > > > +	/* TODO: unmap on stop */
> > > > +	dev->log_base = (uint64_t)(uintptr_t)addr + off;
> > > (uint64_t)(uintptr_t)RTE_PTR_ADD(addr, off)?
> > 
> > No, addr is of (void *) type, we should cast it to uint64_t type first,
> > before adding it with "off".
> > 
> > 	--yliu
> RTE_PTR_ADD is the DPDK interface for pointer arithmetic operation.

log_base is with "uint64_t" type, RTE_PTR_ADD() returns (void*), so it
won't work here.

	--yliu