Re: [Qemu-devel] [PATCH] suppress 'warn_unused_result' warning

[Anthony Liguori <anthony@codemonkey.ws>]

Stuart Brady wrote:
> On Sun, May 10, 2009 at 07:53:35PM -0600, M. Warner Losh wrote:
>   
>> When a signal is received and you are waiting for data, you get
>> EINTR.  If there's data available, then I believe the behavior is to
>> return that data and not EINTR.  That's the way Unix works.
>>     
>
> So if I do a read() from a file over NFS, and there's an awful lot of
> latency (and perhaps even connection problems), and the process gets a
> signal -- does that mean that the signal will only be delivered once
> data is returned?
>
> If not, then I would really start to wonder whether /all/ code dealing
> with read(), write(), etc. should be written to cope with EINTR (and 
> also partial reads/writes?) regardless of whatever is done with threads
> and signal masks, as doing otherwise seems only to be asking for trouble
> at some point.  (I'd be especially concerned about signals intended for
> libraries that are not under the developer's control...)
>   

Any system call can return EINTR just about.  It's not just read/write.

In general, very few systems handle EINTR completely and QEMU is no 
exception here.

More should because SIGHUP is fairly common but I think that for the 
most part, it's sufficiently rare that it's not a problem for most projects.

Regards,

Anthony Liguori