[Qemu-devel] Re: [PATCH v7 3/6] char: Let writers know how much data was written in case of errors

[Anthony Liguori <anthony@codemonkey.ws>]

On 05/05/2010 08:23 AM, Amit Shah wrote:
> On (Wed) May 05 2010 [08:15:19], Anthony Liguori wrote:
>    
>> On 05/04/2010 04:39 PM, Amit Shah wrote:
>>      
>>> On writing errors, we just returned -1 even if some bytes were already
>>> written out. Ensure we return the number of bytes written before we
>>> return the error (on a subsequent call to qemu_chr_write()).
>>>
>>> Signed-off-by: Amit Shah<amit.shah@redhat.com>
>>> ---
>>>    qemu-char.c |   12 +++++++++++-
>>>    1 files changed, 11 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/qemu-char.c b/qemu-char.c
>>> index 76ad12c..decf687 100644
>>> --- a/qemu-char.c
>>> +++ b/qemu-char.c
>>> @@ -507,6 +507,9 @@ int send_all(int fd, const void *buf, int len1)
>>>        while (len>   0) {
>>>            ret = send(fd, buf, len, 0);
>>>            if (ret<   0) {
>>> +            if (len1 - len) {
>>> +                return len1 - len;
>>> +            }
>>>                errno = WSAGetLastError();
>>>                if (errno != WSAEWOULDBLOCK) {
>>>                    return -1;
>>> @@ -531,8 +534,15 @@ static int unix_write(int fd, const uint8_t *buf, int len1)
>>>        while (len>   0) {
>>>            ret = write(fd, buf, len);
>>>            if (ret<   0) {
>>> -            if (errno != EINTR&&   errno != EAGAIN)
>>> +            if (errno == EINTR) {
>>> +                continue;
>>> +            }
>>> +            if (len1 - len) {
>>> +                return len1 - len;
>>> +            }
>>> +            if (errno != EAGAIN) {
>>>                    return -1;
>>> +            }
>>>            } else if (ret == 0) {
>>>                break;
>>>            } else {
>>>
>>>        
>> This will break lots of things.  The contract for send_all and
>> unix_write is that the transmit all data.
>>      
> The current behaviour remains unchanged for all the users. Only callers
> of qemu_chr_write_nb() will get an -EAGAIN return.
>    

No, send_all used to send all data.  After your change, it only sends 
what it can the first time.  The same with unix_write.

Regards,

Anthony Liguori

> 		Amit
>