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Re: [Qemu-devel] [PATCH v3 2/2] qemu-bridge-helper: Use stateless config

From: Ikey Doherty
Subject: Re: [Qemu-devel] [PATCH v3 2/2] qemu-bridge-helper: Use stateless configuration for bridge.conf
Date: Tue, 26 May 2015 17:41:08 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

On 26/05/15 17:38, Eduardo Habkost wrote:
On Tue, May 26, 2015 at 01:54:07PM +0100, Ikey Doherty wrote:
The goal of stateless, and thus this change, is to separate OS configuration
from system administrator configuration. With this change we will read the
default configuration data from /usr/share/defaults/qemu, in the absence of
an overriding site administrator configuration in /etc/qemu.

A key advantage of this change is enabling a sane and immutable default OS
configuration, that is resiliant to upgrades. Ultimate power is still left
to the system administrator, with the ability to override the defaults if
required. Lastly, given that the sane defaults are always available, the
administrator may simply remove their site-config files to reset the
configuration to the "factory defaults" (i.e. OS configuration).

Signed-off-by: Ikey Doherty <address@hidden>
  configure            |  2 ++
  qemu-bridge-helper.c | 15 +++++++++------
  2 files changed, 11 insertions(+), 6 deletions(-)

+#define SITE_ACL_FILE    CONFIG_QEMU_CONFDIR    "/bridge.conf"

  enum {
      ACL_ALLOW = 0,
@@ -272,11 +273,13 @@ int main(int argc, char **argv)

      /* parse default acl file */
-    if (parse_acl_file(DEFAULT_ACL_FILE, &acl_list) == -1) {
-        fprintf(stderr, "failed to parse default acl file `%s'\n",
-                DEFAULT_ACL_FILE);
-        ret = EXIT_FAILURE;
-        goto cleanup;
+    if (parse_acl_file(SITE_ACL_FILE, &acl_list) == -1) {
+        if (parse_acl_file(DEFAULT_ACL_FILE, &acl_list) == -1) {
+            fprintf(stderr, "failed to parse default acl file `%s'\n",
+                    DEFAULT_ACL_FILE);
+            ret = EXIT_FAILURE;
+            goto cleanup;
+        }

This will make syntax errors on SITE_ACL_FILE cause partial loading of
the rules on SITE_ACL_FILE, and trigger loading of DEFAULT_ACL_FILE,
instead of aborting bridge-helper.

Wouldn't it be better to fallback to DEFAULT_ACL_FILE if and only if
SITE_ACL_FILE is missing?

I could stat the file and fallback to default, and only parse_acl_file
the one that exists. Better?

Clear Linux Project for Intel Architecture
Intel Open Source Technology Center

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