[PATCH] qemu_slirp: Check if helper exists before fetching its capabilities

[Michal Privoznik]

I've noticed when running libvirtd in the session mode that
whenever I start a virtual machine the following error is printed
into logs:

  error : cannot execute binary /usr/bin/slirp-helper: No such file or directory

The error message is produced in qemuSlirpNewForHelper() which
does attempt to be a NO-OP if the helper doesn't exist by
checking if its path is NULL, but that's not usually the case
because in the default config (in virQEMUDriverConfigNew()) its
path is initialized to QEMU_SLIRP_HELPER. And while it is true
that during configure we try to get the actual path of the helper
we fallback to the path above if not found.

Fix the check so that the function checks whether the helper
exists and is executable.

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/qemu_slirp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_slirp.c b/src/qemu/qemu_slirp.c
index d2e4ed79be..4e5ab12727 100644
--- a/src/qemu/qemu_slirp.c
+++ b/src/qemu/qemu_slirp.c
@@ -101,7 +101,8 @@ qemuSlirpNewForHelper(const char *helper)
     virJSONValuePtr featuresJSON;
     size_t i, nfeatures;
 
-    if (!helper)
+    if (!helper ||
+        !virFileIsExecutable(helper))
         return NULL;
 
     slirp = qemuSlirpNew();
-- 
2.26.2