[PATCH] tools/xl: don't crash on NULL command line

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

When running xl in a domU, it doesn't have access to the Xen command
line. Before the non-truncating xc_xenver_cmdline(), it was always set
with strdup, possibly of an empty string. Now it's NULL. Treat it the
same as empty cmdline, as it was before. Autoballoon isn't relevant for
xl devd in a domU anyway.

Fixes: 75f91607621c ("tools: Introduce a non-truncating xc_xenver_cmdline()")
Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
So, apparently the "No API/ABI change" was a lie... it changed "empty
string" to NULL in libxl_version_info->commandline. Quick search didn't
spot any other (in-tree) place that could trip on NULL there. IMO NULL
value in this case makes more sense. Buf maybe for the API stability
reasons the old behavior should be restored?

PS I'm working on a CI test for this case (and driver domains in
general). I have it working with Alpine already, but it wouldn't detect
this issue, as musl's regexec() doesn't crash on NULL... So, I'll add a
test on Debian too.
---
 tools/xl/xl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/xl/xl.c b/tools/xl/xl.c
index ec72ca60c32a..e183d42b1d65 100644
--- a/tools/xl/xl.c
+++ b/tools/xl/xl.c
@@ -81,6 +81,8 @@ static int auto_autoballoon(void)
     info = libxl_get_version_info(ctx);
     if (!info)
         return 1; /* default to on */
+    if (!info->commandline)
+        return 1;
 
 #define SIZE_PATTERN "-?[0-9]+[bBkKmMgGtT]?"
 
-- 
2.49.0