Re: [PATCH] qemu: qemu_fopen_fd: differentiate between reader and writer user

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>   
>>> The proposed patch is less that ideal IMO as it introduces
>>> limitations on what you can do with a file.  An alternative
>>> implementation would add a read/write mode to the buffer, based on
>>> the last access type.  When switching from read to write, we drop the
>>> buffer, and when switching from write to read, we flush it and then
>>> drop it.  This is more complex but results in a cleaner API.
>>>       
>> I would think a better solution would introduce two buffers, one for
>> read and one for write.  That way, you can have a proper bidirectional
>> stream.
>>
>>     
>
> Complexity goes way up.  Now you need to intercept reads that go to the
> write buffer, and vice versa.
>   

Yeah, Uri: instead of passing an argument to qemu_fopen_ops, it may be 
better to direct the cases where we do a write and set a flag.  Then in 
the fflush() function, only do the put_buffer if the is_write flag is set.

Also, having checks and the read and write functions to determine if the 
is_write flag is set along with whether buf_index > 0 that fprintf()'d 
and aborted would be good for debugging.

Regards,

Anthony Liguori