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dns-resolve: Improve on handling of system DNS nameserver

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This patch enables OVS on windows to read system nameserver configuration.
In addition, a new environment variable OVS_RESOLV_CONF is introduced.
If set, it can be used as DNS server configuration file. This variable
is supposed to be used for sandboxing other things. It is documented
accordingly.

Suggested-by: Ben Pfaff <blp@ovn.org>
Suggested-by: Mark Michelson <mmichels@redhat.com>
Signed-off-by: Yifeng Sun <pkusunyifeng@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
This commit is contained in:
Yifeng Sun 2018-11-07 13:44:34 -08:00 committed by Ben Pfaff
parent ba8eb43a07
commit 9ce4aa8ee7
3 changed files with 15 additions and 5 deletions
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2
Documentation/intro/install/general.rst
View File

@ -97,6 +97,8 @@ need the following software:
you want to enable ovs-vswitchd and other utilities to use DNS names when
specifying OpenFlow and OVSDB remotes. If unbound library is already
installed, then Open vSwitch will automatically build with support for it.
The environment variable OVS_RESOLV_CONF can be used to specify DNS server
configuration file (the default file on Linux is /etc/resolv.conf).
On Linux, you may choose to compile the kernel module that comes with the Open
vSwitch distribution or to use the kernel module built into the Linux kernel

2
NEWS
View File

@ -16,6 +16,8 @@ Post-v2.10.0
- ovs-vswitchd:
* New configuration option "offload-rebalance", that enables dynamic
rebalancing of offloaded flows.
- The environment variable OVS_RESOLV_CONF, if set, is now used
as the DNS server configuration file.
v2.10.0 - 18 Aug 2018
---------------------

16
lib/dns-resolve.c
View File

@ -82,14 +82,21 @@ dns_resolve_init(bool is_daemon)
return;
}
#ifdef __linux__
const char *filename = "/etc/resolv.conf";
const char *filename = getenv("OVS_RESOLV_CONF");
if (!filename) {
#ifdef _WIN32
/* On Windows, NULL means to use the system default nameserver. */
#else
filename = "/etc/resolv.conf";
#endif
}
struct stat s;
if (!stat(filename, &s) || errno != ENOENT) {
if (!filename || !stat(filename, &s) || errno != ENOENT) {
int retval = ub_ctx_resolvconf(ub_ctx__, filename);
if (retval != 0) {
VLOG_WARN_RL(&rl, "Failed to read %s: %s",
filename, ub_strerror(retval));
filename ? filename : "system default nameserver",
ub_strerror(retval));
ub_ctx_delete(ub_ctx__);
ub_ctx__ = NULL;
return;
@ -101,7 +108,6 @@ dns_resolve_init(bool is_daemon)
ub_ctx__ = NULL;
return;
}
#endif
/* Handles '/etc/hosts' on Linux and 'WINDIR/etc/hosts' on Windows. */
int retval = ub_ctx_hosts(ub_ctx__, NULL);