Messages in this thread | | | Date | Tue, 14 Sep 2010 11:12:23 +0200 | From | Avi Kivity <> | Subject | Re: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host kernel |
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On 09/14/2010 05:17 AM, David Miller wrote: > From: Shirley Ma<mashirle@us.ibm.com> > Date: Mon, 13 Sep 2010 13:48:03 -0700 > >> + base = (unsigned long)from->iov_base + offset1; >> + size = ((base& ~PAGE_MASK) + len + ~PAGE_MASK)>> PAGE_SHIFT; >> + num_pages = get_user_pages_fast(base, size, 0,&page[i]); >> + if ((num_pages != size) || >> + (num_pages> MAX_SKB_FRAGS - skb_shinfo(skb)->nr_frags)) >> + /* put_page is in skb free */ >> + return -EFAULT; > What keeps the user from writing to these pages in it's address space > after the write call returns? > > A write() return of success means: > > "I wrote what you gave to me" > > not > > "I wrote what you gave to me, oh and BTW don't touch these > pages for a while." > > In fact "a while" isn't even defined in any way, as there is no way > for the write() invoker to know when the networking card is done with > those pages.
That's what io_submit() is for. Then io_getevents() tells you what "a while" actually was.
-- error compiling committee.c: too many arguments to function
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