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Message-ID: <20141106173012.GY7996@ZenIV.linux.org.uk> Date: Thu, 6 Nov 2014 17:30:12 +0000 From: Al Viro <viro@...IV.linux.org.uk> To: Herbert Xu <herbert@...dor.apana.org.au> Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, bcrl@...ck.org, YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org> Subject: Re: [PATCH 1/4] inet: Add skb_copy_datagram_iter On Thu, Nov 06, 2014 at 04:28:18PM +0800, Herbert Xu wrote: > + if (copy_to_iter(skb->data + offset, copy, to)) > + goto fault; Sorry, no - copy_to_iter() returns the number of bytes copied, not 0 or -EFAULT. > + vaddr = kmap(page); > + err = copy_to_iter(vaddr + frag->page_offset + > + offset - start, copy, to); > + kunmap(page); > + if (err) > + goto fault; And that one should be copied = copy_page_to_iter(page, frag->page_offset + offset - start, copy, to); if (copied != copy) goto fault; Don't bother with kmap(), vaddr and all that shite. The primitive is copy_page_to_iter(page, offset_in_page, nbytes, iter) it does all needed kmap itself and it's smart enough to use kmap_atomic when it can get away with that. Similar for copy_page_from_iter(). Both of those (as well as copy_{to,from}_iter()) advance iov_iter and return the number of bytes actually copied. So the check for EFAULT is "it has copied less than you've asked it to copy *and* you haven't run out that iov_iter". The second part is guaranteed to be true in this case - your code makes sure that 'copy' is no more than the space left in iterator. In general, this check would be spelled if (copied != copy && iov_iter_count(to)) goto fault; -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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