[PULL 4/5] softmmu/vl: Allow -fw_cfg 'gen_id' option to use the 'etc/' namespace

[Philippe Mathieu-Daudé]

Names of user-provided fw_cfg items are supposed to start
with "opt/". However FW_CFG_DATA_GENERATOR items are generated
by QEMU, so allow the "etc/" namespace in this specific case.

Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20200623172726.21040-5-philmd@redhat.com>
---
 docs/specs/fw_cfg.txt | 4 ++++
 softmmu/vl.c          | 8 +++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/docs/specs/fw_cfg.txt b/docs/specs/fw_cfg.txt
index bc16daa38a..3e6d586f66 100644
--- a/docs/specs/fw_cfg.txt
+++ b/docs/specs/fw_cfg.txt
@@ -258,4 +258,8 @@ Prefix "opt/org.qemu/" is reserved for QEMU itself.
 Use of names not beginning with "opt/" is potentially dangerous and
 entirely unsupported.  QEMU will warn if you try.
 
+Use of names not beginning with "opt/" is tolerated with 'gen_id' (that
+is, the warning is suppressed), but you must know exactly what you're
+doing.
+
 All externally provided fw_cfg items are read-only to the guest.
diff --git a/softmmu/vl.c b/softmmu/vl.c
index 13cada39d6..159f0352a9 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -2049,7 +2049,13 @@ static int parse_fw_cfg(void *opaque, QemuOpts *opts, 
Error **errp)
                    FW_CFG_MAX_FILE_PATH - 1);
         return -1;
     }
-    if (strncmp(name, "opt/", 4) != 0) {
+    if (nonempty_str(gen_id)) {
+        /*
+         * In this particular case where the content is populated
+         * internally, the "etc/" namespace protection is relaxed,
+         * so do not emit a warning.
+         */
+    } else if (strncmp(name, "opt/", 4) != 0) {
         warn_report("externally provided fw_cfg item names "
                     "should be prefixed with \"opt/\"");
     }
-- 
2.21.3