Re: [PATCH] fix migration failure with xl migrate --debug

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 26/11/2014 20:51, M A Young wrote:
> Migrations with xl migrate --debug will fail because debugging
> information from the receiving process is written to the stdout
> channel. This channel is also used for status messages so the
> migration will fail as the sending process receives an unexpected
> message. This patch moves the debugging information to the stderr
> channel.
>
> Signed-off-by: Michael Young <m.a.young@durham.ac.uk>

Ah yes - that will do.

The whole info/error/debug handling here is a mess.  Amongst other
issues, it is not possible to distinguish whether libxc logging messages
are coming from the sending or receiving side, without judging the
context from the text itself.

>
> Use stderr for debugging messages for xl migrate --debug as stdout is used
> for status messages.
>
> --- xen-4.5.0-rc1/tools/libxl/xl_cmdimpl.c.orig	2014-10-24 15:22:40.000000000 +0100
> +++ xen-4.5.0-rc1/tools/libxl/xl_cmdimpl.c	2014-11-25 20:29:06.723856433 +0000
> @@ -383,7 +383,7 @@

Sadly, changing printf_info() like this has an unintended knock-on
effect to create_domain() (xl create, migrate-recevive, restore) and xl
config-update.  I think you might have to pass FILE pointers all the way
through.

>                          libxl_domain_config *d_config)
>  {
>      if (output_format == OUTPUT_FORMAT_SXP)
> -        return printf_info_sexp(domid, d_config);
> +        return printf_info_sexp(domid, d_config, stderr);
>  
>      const char *buf;
>      libxl_yajl_length len = 0;
> @@ -404,7 +404,7 @@
>      if (s != yajl_gen_status_ok)
>          goto out;
>  
> -    puts(buf);
> +    fputs(buf,stderr);

puts() and fputs() are not quite synonymous.  puts() will
unconditionally add an extra newline to stdout.  It is unclear whether
the string from yajl_gen_get_buf() comes with a trailing newline or
not.  If the output looks ok, it probably is fine.

~Andrew

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