Re: Setup patch to keep test version if test version installed

[Eric Blake <eblake at redhat dot com>]

On 02/06/2015 02:24 AM, Corinna Vinschen wrote:
> On Feb  5 22:57, Achim Gratz wrote:
>>
>> Oh, and while you are so deep in the bowels of setup.exe, would it be
>> possible to somehow fake a pty to shell scripts and a console to cmd so
>> that the scripts run by setup.exe produce their output in line-buffered
>> instead of fully buffered mode?
> 
> Er... uh... *cough*... PTC?
> 
> For Cygwin processes this would require to duplicate lots of the pty
> code from Cygwin to Setup.  For native commands it might be enough to
> play with the process creation flags in the call to CreateProcess, but
> that might lead to a flickering taskbar entry for a hidden console.

For native commands (.bat, .cmd postinstalls), I have no idea.  But for
cygwin processes (.sh postinstalls), it would be neat if we could get
coreutils' stdbuf utility working on cygwin, then we just invoke 'sh -c
"stdbuf script.sh"' instead of 'sh -c "script.sh"'.

> 
> The other problem is that the stdio handles are redirected to a file
> and thus, even if you have a console or pty, the output from the command
> will use fully buffered mode.
> 
> The only way around that, afaics, is some sort of global setting (env
> var?) for the buffering mode which is honored by native processes and
> which may be read by the Cygwin DLL as well to enforce line buffering.
> But I'm not aware such a setting exists.

stdbuf uses LD_PRELOAD to tell a process in main() that it should use
line or no buffering, regardless of whether the output file is a file.
And cygwin supports LD_PRELOAD.  But to date, no one has helped figure
out how to port it to cygwin (I assume it should work, but have not had
time to try it - the difficulties lie more in getting the coreutils
Makefile to target the difference in cygwin naming with .dll instead of
.so and with .exe suffixes to worry about).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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