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From:   Olaf Hering <olaf@aepfle.de>
To:     "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Sasha Levin <sashal@kernel.org>,
        linux-hyperv@vger.kernel.org (open list:Hyper-V CORE AND DRIVERS),
        linux-kernel@vger.kernel.org (open list)
Cc:     Olaf Hering <olaf@aepfle.de>
Subject: [PATCH v1] tools/hv: async name resolution in kvp_daemon
Date:   Thu, 24 Oct 2019 16:49:43 +0200
Message-Id: <20191024144943.26199-1-olaf@aepfle.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The hostname is resolved just once since commit 58125210ab3b ("Tools:
hv: cache FQDN in kvp_daemon to avoid timeouts") to make sure the VM
responds within the timeout limits to requests from the host.

If for some reason getaddrinfo fails, the string returned by the
"FullyQualifiedDomainName" request contains some error string, which is
then used by tools on the host side.

Adjust the code to resolve the current hostname in a separate thread.
This thread loops until getaddrinfo returns success. During this time
all "FullyQualifiedDomainName" requests will be answered with an empty
string.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 tools/hv/Makefile        |  2 ++
 tools/hv/hv_kvp_daemon.c | 69 ++++++++++++++++++++++++++++++++----------------
 2 files changed, 48 insertions(+), 23 deletions(-)

diff --git a/tools/hv/Makefile b/tools/hv/Makefile
index b57143d9459c..3b5481015a84 100644
--- a/tools/hv/Makefile
+++ b/tools/hv/Makefile
@@ -22,6 +22,8 @@ ALL_PROGRAMS := $(patsubst %,$(OUTPUT)%,$(ALL_TARGETS))
 
 ALL_SCRIPTS := hv_get_dhcp_info.sh hv_get_dns_info.sh hv_set_ifconfig.sh
 
+$(OUTPUT)hv_kvp_daemon: LDFLAGS += -lpthread
+
 all: $(ALL_PROGRAMS)
 
 export srctree OUTPUT CC LD CFLAGS
diff --git a/tools/hv/hv_kvp_daemon.c b/tools/hv/hv_kvp_daemon.c
index e9ef4ca6a655..22cf1c4dbf5c 100644
--- a/tools/hv/hv_kvp_daemon.c
+++ b/tools/hv/hv_kvp_daemon.c
@@ -41,6 +41,7 @@
 #include <net/if.h>
 #include <limits.h>
 #include <getopt.h>
+#include <pthread.h>
 
 /*
  * KVP protocol: The user mode component first registers with the
@@ -85,7 +86,7 @@ static char *processor_arch;
 static char *os_build;
 static char *os_version;
 static char *lic_version = "Unknown version";
-static char full_domain_name[HV_KVP_EXCHANGE_MAX_VALUE_SIZE];
+static char *full_domain_name;
 static struct utsname uts_buf;
 
 /*
@@ -1327,27 +1328,53 @@ static int kvp_set_ip_info(char *if_name, struct hv_kvp_ipaddr_value *new_val)
 	return error;
 }
 
-
-static void
-kvp_get_domain_name(char *buffer, int length)
+/*
+ * Async retrival of Fully Qualified Domain Name because getaddrinfo takes an
+ * unpredictable amount of time to finish.
+ */
+static void *kvp_getaddrinfo(void *p)
 {
-	struct addrinfo	hints, *info ;
-	int error = 0;
+	char *tmp, **str_ptr = (char **)p;
+	char hostname[HOST_NAME_MAX + 1];
+	struct addrinfo	*info, hints = {
+		.ai_family = AF_INET, /* Get only ipv4 addrinfo. */
+		.ai_socktype = SOCK_STREAM,
+		.ai_flags = AI_CANONNAME,
+	};
+	int ret;
+
+	if (gethostname(hostname, sizeof(hostname) - 1) < 0)
+		goto out;
+
+	do {
+		ret = getaddrinfo(hostname, NULL, &hints, &info);
+		if (ret)
+			sleep(1);
+	} while (ret);
+
+	ret = asprintf(&tmp, "%s", info->ai_canonname);
+	freeaddrinfo(info);
+	if (ret <= 0)
+		goto out;
+
+	if (ret > HV_KVP_EXCHANGE_MAX_VALUE_SIZE)
+		tmp[HV_KVP_EXCHANGE_MAX_VALUE_SIZE - 1] = '\0';
+	*str_ptr = tmp;
 
-	gethostname(buffer, length);
-	memset(&hints, 0, sizeof(hints));
-	hints.ai_family = AF_INET; /*Get only ipv4 addrinfo. */
-	hints.ai_socktype = SOCK_STREAM;
-	hints.ai_flags = AI_CANONNAME;
+out:
+	pthread_exit(NULL);
+}
+
+static void kvp_obtain_domain_name(char **str_ptr)
+{
+	pthread_t t;
 
-	error = getaddrinfo(buffer, NULL, &hints, &info);
-	if (error != 0) {
-		snprintf(buffer, length, "getaddrinfo failed: 0x%x %s",
-			error, gai_strerror(error));
+	if (pthread_create(&t, NULL, kvp_getaddrinfo, str_ptr)) {
+		syslog(LOG_ERR, "pthread_create failed; error: %d %s",
+			errno, strerror(errno));
 		return;
 	}
-	snprintf(buffer, length, "%s", info->ai_canonname);
-	freeaddrinfo(info);
+	pthread_detach(t);
 }
 
 void print_usage(char *argv[])
@@ -1412,11 +1439,7 @@ int main(int argc, char *argv[])
 	 * Retrieve OS release information.
 	 */
 	kvp_get_os_info();
-	/*
-	 * Cache Fully Qualified Domain Name because getaddrinfo takes an
-	 * unpredictable amount of time to finish.
-	 */
-	kvp_get_domain_name(full_domain_name, sizeof(full_domain_name));
+	kvp_obtain_domain_name(&full_domain_name);
 
 	if (kvp_file_init()) {
 		syslog(LOG_ERR, "Failed to initialize the pools");
@@ -1571,7 +1594,7 @@ int main(int argc, char *argv[])
 
 		switch (hv_msg->body.kvp_enum_data.index) {
 		case FullyQualifiedDomainName:
-			strcpy(key_value, full_domain_name);
+			strcpy(key_value, full_domain_name ? : "");
 			strcpy(key_name, "FullyQualifiedDomainName");
 			break;
 		case IntegrationServicesVersion: