vl: defuse PID file path resolve error

Commit 85c4bf8aa6 ("vl: Unlink absolute PID file path") introduced a
critical error when the PID file path cannot be resolved. Before this
commit, it was possible to invoke QEMU when the PID file was a file
created with mkstemp that was already unlinked at the time of the
invocation. There might be other similar scenarios.

It should not be a critical error when the PID file unlink notifier
can't be registered, because the path can't be resolved. If the file
is already gone from QEMU's perspective, silently ignore the error.
Otherwise, only print a warning.

Fixes: 85c4bf8aa6 ("vl: Unlink absolute PID file path")
Reported-by: Dominik Csapak <d.csapak@proxmox.com>
Suggested-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20221031094716.39786-1-f.ebner@proxmox.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/softmmu/vl.c b/softmmu/vl.c
index 3340f63c37..ea20b23e4c 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -2465,10 +2465,11 @@ static void qemu_maybe_daemonize(const char *pid_file)
 
         pid_file_realpath = g_malloc0(PATH_MAX);
         if (!realpath(pid_file, pid_file_realpath)) {
-            error_report("cannot resolve PID file path: %s: %s",
-                         pid_file, strerror(errno));
-            unlink(pid_file);
-            exit(1);
+            if (errno != ENOENT) {
+                warn_report("not removing PID file on exit: cannot resolve PID "
+                            "file path: %s: %s", pid_file, strerror(errno));
+            }
+            return;
         }
 
         qemu_unlink_pidfile_notifier = (struct UnlinkPidfileNotifier) {