[libvirt] [PATCH 1/3] Autodetect if the remote nc command supports the -q option

[Guido Günther]

Hi Eric,

On Wed, Oct 12, 2011 at 05:03:45PM -0600, Eric Blake wrote:
> On 10/12/2011 04:39 PM, Guido Günther wrote:
> >Based on a patch by Marc Deslauriers<marc.deslauriers at ubuntu.com>
> >
> >RH: https://bugzilla.redhat.com/show_bug.cgi?id=562176
> >Ubuntu: https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/517478
> >Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=573172
> >---
> >  src/rpc/virnetsocket.c   |   23 ++++++++++++++++++++---
> >  tests/virnetsockettest.c |   11 ++++++-----
> >  2 files changed, 26 insertions(+), 8 deletions(-)
> >
> >+    virCommandAddArgList(cmd, nodename, "sh", "-c", NULL);
> >+    /*
> >+     * This ugly thing is a shell script to detect availability of
> >+     * the -q option for 'nc': debian and suse based distros need this
> >+     * flag to ensure the remote nc will exit on EOF, so it will go away
> >+     * when we close the connection tunnel. If it doesn't go away, subsequent
> >+     * connection attempts will hang.
> >+     *
> >+     * Fedora's 'nc' doesn't have this option, and defaults to the desired
> >+     * behavior.
> >+     */
> 
> The comment is essential :)
> 
> >+    virCommandAddArgFormat(cmd,
> >+         "'if %s -q 2>&1 | grep \"requires an argument\">/dev/null 2>&1; then"
> >+         "     ARG=-q0;"
> >+         "fi;"
> >+         "%s $ARG -U %s'",
> 
> This relies on ARG not being inherited from the environment.
> Probably safe, but just out of paranoia, and in a desire to compress
> things a bit, I'd go with either a pre-initialization:
> 
> s/'if %s/'ARG=;if %s/
> 
> or an else clause to the if-then-fi.

I went for the else clause since I think it's best for readability.

> 
> Also, since we aren't using any space after ;, why do we need four
> spaces before ARG=-q0?  We need at least one space (or a newline)
> after 'then', but either we should use newline after each part of
> the command (to match how it is listed in the source) or compress
> things to minimal size.
> 
> >+         netcat ? netcat : "nc",
> >+         netcat ? netcat : "nc",
> 
> Micro-optimization: prior to the virCommandAddArgFormat, I would have done:
> 
> if (!netcat)
>     netcat = "nc";

Done.

> 
> then just directly used netcat here instead of dual ?:.  But that's
> a nit that you don't have to worry about (patch 3/3 does the same
> thing).
> 
> >+++ b/tests/virnetsockettest.c
> >@@ -496,7 +496,7 @@ mymain(void)
> >      struct testSSHData sshData1 = {
> >          .nodename = "somehost",
> >          .path = "/tmp/socket",
> >-        .expectOut = "somehost nc -U /tmp/socket\n",
> >+        .expectOut = "somehost sh -c 'if nc -q 2>&1 | grep \"requires an argument\">/dev/null 2>&1; then     ARG=-q0;fi;nc $ARG -U /tmp/socket'\n",
> 
> Feel free to break this into multiple string literals; along
> expected newline boundaries might be nice:
> 
> .expectOut = "somehost sh -c "
>     "'if ...; then\n"
>     "    ARG=-q0\n"
>     "fi\n"
>     "nc $ARG ...";

Done.

> 
> (or whatever it takes to match any changes you make above).
> 
> ACK with nits fixed.

New version attached.
Cheers,
 -- Guido
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