From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wen Congyang Subject: Re: [Patch v3 2/2] tools/libxc: Implement writev_exact() in the same style as write_exact() Date: Fri, 18 Jul 2014 18:05:20 +0800 Message-ID: <53C8F160.7040005@cn.fujitsu.com> References: <1405521126-17035-1-git-send-email-andrew.cooper3@citrix.com> <1405521126-17035-2-git-send-email-andrew.cooper3@citrix.com> <53C874DF.2040903@cn.fujitsu.com> <53C8E6DD.4080207@citrix.com> <1405677220.13883.10.camel@kazak.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1405677220.13883.10.camel@kazak.uk.xensource.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 , Andrew Cooper Cc: Ian Jackson , Xen-devel List-Id: xen-devel@lists.xenproject.org At 07/18/2014 05:53 PM, Ian Campbell Wrote: > On Fri, 2014-07-18 at 10:20 +0100, Andrew Cooper wrote: >> On 18/07/14 02:14, Wen Congyang wrote: >>> At 07/16/2014 10:32 PM, Andrew Cooper Wrote: >>>> This implementation of writev_exact() will cope with an iovcnt greater than >>>> IOV_MAX because glibc will actually let this work anyway, and it is very >>>> useful not to have to work about this in the caller of writev_exact(). The >>>> caller is still required to ensure that the sum of iov_len's doesn't overflow >>>> a ssize_t. >>>> >>>> Signed-off-by: Andrew Cooper >>>> CC: Ian Campbell >>>> CC: Ian Jackson >>>> >>>> --- >>>> v3: >>>> * Re-add adjustment for partial writes. >>>> * Split min/max adjustment into separate patch. >>>> >>>> v2: >>>> * Remove adjustment for partial writes of a specific iov[] entry. >>>> --- >>>> tools/libxc/xc_private.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++ >>>> tools/libxc/xc_private.h | 2 ++ >>>> 2 files changed, 62 insertions(+) >>>> >>>> diff --git a/tools/libxc/xc_private.c b/tools/libxc/xc_private.c >>>> index 1c214dd..0941b06 100644 >>>> --- a/tools/libxc/xc_private.c >>>> +++ b/tools/libxc/xc_private.c >>>> @@ -858,6 +858,66 @@ int write_exact(int fd, const void *data, size_t size) >>>> return 0; >>>> } >>>> >>>> +int writev_exact(int fd, const struct iovec *iov, int iovcnt) >>>> +{ >>>> + struct iovec *local_iov = NULL; >>>> + int rc = 0, iov_idx = 0, saved_errno = 0; >>>> + ssize_t len; >>>> + >>>> + while ( iov_idx < iovcnt ) >>>> + { >>>> + /* Skip over iov[] entries with 0 length. */ >>>> + while ( iov[iov_idx].iov_len == 0 ) >>>> + if ( ++iov_idx == iovcnt ) >>>> + goto out; >>> set saved_errn to 0 before goto out? >> >> Good catch. > > Isn't this a success path? errno is generally undefined on success. Yes, but we set saved_errno to 0 here: > + saved_errno = 0; > + > + out: > + free(local_iov); > + errno = saved_errno; > + return rc; > +} I think there is no need to save errno in this function, because we return -1 when writev()/malloc() fails. Another problem: > + local_iov = malloc(iovcnt * sizeof(*iov)); > + if ( !local_iov ) > + { > + saved_errno = ENOMEM; > + goto out; > + } > + rc is not set to -1 before goto out. Thanks Wen Congyang > > Ian. > > . >