From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [Patch v3 2/2] tools/libxc: Implement
 writev_exact() in the same style as write_exact()
Date: Fri, 18 Jul 2014 10:20:29 +0100
Message-ID: <53C8E6DD.4080207@citrix.com>
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To: Wen Congyang <wency@cn.fujitsu.com>, Xen-devel <xen-devel@lists.xen.org>
Cc: Ian Jackson <Ian.Jackson@eu.citrix.com>, Ian Campbell <Ian.Campbell@citrix.com>
List-Id: xen-devel@lists.xenproject.org

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 <andrew.cooper3@citrix.com>
>> CC: Ian Campbell <Ian.Campbell@citrix.com>
>> CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
>>
>> ---
>> 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.

~Andrew