Re: [Bug-readline] [PATCH] readline/histfile.c: Check and retry write() operation in history_truncate_file()

[Chet Ramey <chet dot ramey at case dot edu>]

On 6/20/14, 4:57 AM, Chen Gang wrote:
> On 06/19/2014 09:31 AM, Chen Gang wrote:
>>
>>
>> On 06/19/2014 04:33 AM, Chet Ramey wrote:
>>> On 6/10/14, 10:35 PM, Chen Gang wrote:
>>>> For regular file, write() operation may also fail, so check it too. If
>>>> write() return 0, can simply wait and try again, it should not suspend
>>>> infinitely if environments have no critical issues.
>>>
>>> Readline-6.3 checks the return value from write() and returns a non-zero
>>> value to the history_truncate_file caller.  I really don't think that
>>> waiting forever if write continues to return 0 is a great idea; an error
>>> return is enough to let the caller deal with it.
>>>
> 
> Oh, sorry, after think of again, for me, we have to waiting forever if
> write() continues to return 0.

There aren't really any plausible conditions under which write(2) returns
0 instead of -1 when writing a non-zero number of bytes to a regular file.

> 
> When this case happens, the file is already truncated, and the left data
> which is writing to file will be free after return from
> history_truncate_file().
> 
> If return an error code in this case, the caller can not deal with it --
> the log data which should be remained, have been lost, can not get them
> back again.

However, you're right about the data being lost if write fails and returns
-1. Since the sequence of operations is open-read-close-open-write-close, I
think I will change the code for the next version to use a scheme similar
to history_do_write() and restore the original version of the file if the
write fails.

Chet

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/