From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH v5] tools/libxc: Implement writev_exact() in the same style as write_exact() Date: Thu, 19 Feb 2015 18:20:57 +0000 Message-ID: <54E62989.6030006@citrix.com> References: <1424346333-13716-1-git-send-email-andrew.cooper3@citrix.com> <1424363980.30924.125.camel@citrix.com> <54E61620.1080207@citrix.com> <1424365282.30924.136.camel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1424365282.30924.136.camel@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: Wei Liu , Ian Jackson , Xen-devel List-Id: xen-devel@lists.xenproject.org On 19/02/15 17:01, Ian Campbell wrote: > On Thu, 2015-02-19 at 16:58 +0000, Andrew Cooper wrote: >> On 19/02/15 16:39, Ian Campbell wrote: >>> On Thu, 2015-02-19 at 11:45 +0000, Andrew Cooper wrote: >>> >>>> + while ( iov_idx < iovcnt ) >>>> + { >>>> + /* Skip over iov[] entries with 0 length. */ >>>> + while ( iov[iov_idx].iov_len == 0 ) >>>> + if ( ++iov_idx == iovcnt ) >>>> + goto out; >>> Is this required for some reason or just an optimisation? >> Experimentally, submitting a writev() with every iov of length 0 results >> in an EINVAL on CentOS 5.x > How exciting! > >> This causes a failure if a partial write adjustment happens and only iov >> entries of length 0 remain in the set. > If only entries of length 0 remain then isn't that a complete-write of > the final non-empty entry? Hmm - I think you are right. This loop might now be redundant with the partial iov[] handling below. That bit of code did the hokey-cokey several times. On the other hand, I seem to remember that it ended up like this very deliberately, and that I couldn't cover the edge case with only one loop. I think I am going to have to debug this back into existence again. ~Andrew