Tools: hv: Reopen the devices if read() or write() returns errors

The state machine in the hv_utils driver can run out of order in some
corner cases, e.g. if the kvp daemon doesn't call write() fast enough
due to some reason, kvp_timeout_func() can run first and move the state
to HVUTIL_READY; next, when kvp_on_msg() is called it returns -EINVAL
since kvp_transaction.state is smaller than HVUTIL_USERSPACE_REQ; later,
the daemon's write() gets an error -EINVAL, and the daemon will exit().

We can reproduce the issue by sending a SIGSTOP signal to the daemon, wait
for 1 minute, and send a SIGCONT signal to the daemon: the daemon will
exit() quickly.

We can fix the issue by forcing a reset of the device (which means the
daemon can close() and open() the device again) and doing extra necessary
clean-up.

Signed-off-by: Dexuan Cui <[e-mail]>
Reviewed-by: Michael Kelley <[e-mail]>
Signed-off-by: Sasha Levin <[e-mail]>

tools/hv/hv_fcopy_daemon.c

···
 
 	error = 0;
 done:
+	if (error)
+		target_fname[0] = '\0';
 	return error;
 }
 
···
 	return ret;
 }
 
+/*
+ * Reset target_fname to "" in the two below functions for hibernation: if
+ * the fcopy operation is aborted by hibernation, the daemon should remove the
+ * partially-copied file; to achieve this, the hv_utils driver always fakes a
+ * CANCEL_FCOPY message upon suspend, and later when the VM resumes back,
+ * the daemon calls hv_copy_cancel() to remove the file; if a file is copied
+ * successfully before suspend, hv_copy_finished() must reset target_fname to
+ * avoid that the file can be incorrectly removed upon resume, since the faked
+ * CANCEL_FCOPY message is spurious in this case.
+ */
 static int hv_copy_finished(void)
 {
 	close(target_fd);
+	target_fname[0] = '\0';
 	return 0;
 }
 static int hv_copy_cancel(void)
 {
 	close(target_fd);
-	unlink(target_fname);
+	if (strlen(target_fname) > 0) {
+		unlink(target_fname);
+		target_fname[0] = '\0';
+	}
 	return 0;
 
 }
···
 
 int main(int argc, char *argv[])
 {
-	int fcopy_fd;
+	int fcopy_fd = -1;
 	int error;
 	int daemonize = 1, long_index = 0, opt;
 	int version = FCOPY_CURRENT_VERSION;
···
 		struct hv_do_fcopy copy;
 		__u32 kernel_modver;
 	} buffer = { };
-	int in_handshake = 1;
+	int in_handshake;
 
 	static struct option long_options[] = {
 		{"help",	no_argument,	   0,  'h' },
···
 	openlog("HV_FCOPY", 0, LOG_USER);
 	syslog(LOG_INFO, "starting; pid is:%d", getpid());
 
+reopen_fcopy_fd:
+	if (fcopy_fd != -1)
+		close(fcopy_fd);
+	/* Remove any possible partially-copied file on error */
+	hv_copy_cancel();
+	in_handshake = 1;
 	fcopy_fd = open("/dev/vmbus/hv_fcopy", O_RDWR);
 
 	if (fcopy_fd < 0) {
···
 		len = pread(fcopy_fd, &buffer, sizeof(buffer), 0);
 		if (len < 0) {
 			syslog(LOG_ERR, "pread failed: %s", strerror(errno));
-			exit(EXIT_FAILURE);
+			goto reopen_fcopy_fd;
 		}
 
 		if (in_handshake) {
···
 
 		}
 
+		/*
+		 * pwrite() may return an error due to the faked CANCEL_FCOPY
+		 * message upon hibernation. Ignore the error by resetting the
+		 * dev file, i.e. closing and re-opening it.
+		 */
 		if (pwrite(fcopy_fd, &error, sizeof(int), 0) != sizeof(int)) {
 			syslog(LOG_ERR, "pwrite failed: %s", strerror(errno));
-			exit(EXIT_FAILURE);
+			goto reopen_fcopy_fd;
 		}
 	}
 }

tools/hv/hv_kvp_daemon.c

···
 	DNS
 };
 
-static int in_hand_shake = 1;
+static int in_hand_shake;
 
 static char *os_name = "";
 static char *os_major = "";
···
 
 int main(int argc, char *argv[])
 {
-	int kvp_fd, len;
+	int kvp_fd = -1, len;
 	int error;
 	struct pollfd pfd;
 	char    *p;
···
 	openlog("KVP", 0, LOG_USER);
 	syslog(LOG_INFO, "KVP starting; pid is:%d", getpid());
 
-	kvp_fd = open("/dev/vmbus/hv_kvp", O_RDWR | O_CLOEXEC);
-
-	if (kvp_fd < 0) {
-		syslog(LOG_ERR, "open /dev/vmbus/hv_kvp failed; error: %d %s",
-			errno, strerror(errno));
-		exit(EXIT_FAILURE);
-	}
-
 	/*
 	 * Retrieve OS release information.
 	 */
···
 
 	if (kvp_file_init()) {
 		syslog(LOG_ERR, "Failed to initialize the pools");
+		exit(EXIT_FAILURE);
+	}
+
+reopen_kvp_fd:
+	if (kvp_fd != -1)
+		close(kvp_fd);
+	in_hand_shake = 1;
+	kvp_fd = open("/dev/vmbus/hv_kvp", O_RDWR | O_CLOEXEC);
+
+	if (kvp_fd < 0) {
+		syslog(LOG_ERR, "open /dev/vmbus/hv_kvp failed; error: %d %s",
+		       errno, strerror(errno));
 		exit(EXIT_FAILURE);
 	}
 
···
 		if (len != sizeof(struct hv_kvp_msg)) {
 			syslog(LOG_ERR, "read failed; error:%d %s",
 			       errno, strerror(errno));
-
-			close(kvp_fd);
-			return EXIT_FAILURE;
+			goto reopen_kvp_fd;
 		}
 
 		/*
···
 			break;
 		}
 
-		/* Send the value back to the kernel. */
+		/*
+		 * Send the value back to the kernel. Note: the write() may
+		 * return an error due to hibernation; we can ignore the error
+		 * by resetting the dev file, i.e. closing and re-opening it.
+		 */
 kvp_done:
 		len = write(kvp_fd, hv_msg, sizeof(struct hv_kvp_msg));
 		if (len != sizeof(struct hv_kvp_msg)) {
 			syslog(LOG_ERR, "write failed; error: %d %s", errno,
 			       strerror(errno));
-			exit(EXIT_FAILURE);
+			goto reopen_kvp_fd;
 		}
 	}
 

tools/hv/hv_vss_daemon.c

···
 #include <stdbool.h>
 #include <dirent.h>
 
+static bool fs_frozen;
+
 /* Don't use syslog() in the function since that can cause write to disk */
 static int vss_do_freeze(char *dir, unsigned int cmd)
 {
···
 			continue;
 		}
 		error |= vss_do_freeze(ent->mnt_dir, cmd);
-		if (error && operation == VSS_OP_FREEZE)
-			goto err;
+		if (operation == VSS_OP_FREEZE) {
+			if (error)
+				goto err;
+			fs_frozen = true;
+		}
 	}
 
 	endmntent(mounts);
 
 	if (root_seen) {
 		error |= vss_do_freeze("/", cmd);
-		if (error && operation == VSS_OP_FREEZE)
-			goto err;
+		if (operation == VSS_OP_FREEZE) {
+			if (error)
+				goto err;
+			fs_frozen = true;
+		}
 	}
+
+	if (operation == VSS_OP_THAW && !error)
+		fs_frozen = false;
 
 	goto out;
 err:
···
 		endmntent(mounts);
 	}
 	vss_operate(VSS_OP_THAW);
+	fs_frozen = false;
 	/* Call syslog after we thaw all filesystems */
 	if (ent)
 		syslog(LOG_ERR, "FREEZE of %s failed; error:%d %s",
···
 
 int main(int argc, char *argv[])
 {
-	int vss_fd, len;
+	int vss_fd = -1, len;
 	int error;
 	struct pollfd pfd;
 	int	op;
 	struct hv_vss_msg vss_msg[1];
 	int daemonize = 1, long_index = 0, opt;
-	int in_handshake = 1;
+	int in_handshake;
 	__u32 kernel_modver;
 
 	static struct option long_options[] = {
···
 	openlog("Hyper-V VSS", 0, LOG_USER);
 	syslog(LOG_INFO, "VSS starting; pid is:%d", getpid());
 
+reopen_vss_fd:
+	if (vss_fd != -1)
+		close(vss_fd);
+	if (fs_frozen) {
+		if (vss_operate(VSS_OP_THAW) || fs_frozen) {
+			syslog(LOG_ERR, "failed to thaw file system: err=%d",
+			       errno);
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	in_handshake = 1;
 	vss_fd = open("/dev/vmbus/hv_vss", O_RDWR);
 	if (vss_fd < 0) {
 		syslog(LOG_ERR, "open /dev/vmbus/hv_vss failed; error: %d %s",
···
 		if (len != sizeof(struct hv_vss_msg)) {
 			syslog(LOG_ERR, "read failed; error:%d %s",
 			       errno, strerror(errno));
-			close(vss_fd);
-			return EXIT_FAILURE;
+			goto reopen_vss_fd;
 		}
 
 		op = vss_msg->vss_hdr.operation;
···
 		default:
 			syslog(LOG_ERR, "Illegal op:%d\n", op);
 		}
+
+		/*
+		 * The write() may return an error due to the faked VSS_OP_THAW
+		 * message upon hibernation. Ignore the error by resetting the
+		 * dev file, i.e. closing and re-opening it.
+		 */
 		vss_msg->error = error;
 		len = write(vss_fd, vss_msg, sizeof(struct hv_vss_msg));
 		if (len != sizeof(struct hv_vss_msg)) {
 			syslog(LOG_ERR, "write failed; error: %d %s", errno,
 			       strerror(errno));
-
-			if (op == VSS_OP_FREEZE)
-				vss_operate(VSS_OP_THAW);
+			goto reopen_vss_fd;
 		}
 	}