discover/ipmi: Use advisory locking on ipmi device

The ipmi module is shared between pb-config and pb-discover. During
system initilisation, we're likely to have a few invocations of
pb-config running, as well as pb-discover starting.

We may have multiple potential concurrent accesses to the ipmi device
node. To avoid problems, this change introduces a fcntl lock on the
device node.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

1 files changed, 22 insertions, 4 deletions

diff --git a/discover/ipmi.c b/discover/ipmi.c
index 710a47d..54d4e06 100644
--- a/discover/ipmi.c
+++ b/discover/ipmi.c
@@ -107,11 +107,21 @@ int ipmi_transaction(struct ipmi *ipmi, uint8_t netfn, uint8_t cmd,
 {
 	struct timeval start, now, delta;
 	struct pollfd pollfds[1];
+	struct flock lock;
 	int expired_ms, rc;
 
+	memset(&lock, 0, sizeof(lock));
+	lock.l_type = F_WRLCK;
+	lock.l_whence = SEEK_SET;
+	rc = fcntl(ipmi->fd, F_SETLKW, &lock);
+	if (rc == -1) {
+		pb_log("IPMI: error locking IPMI device: %m\n");
+		return rc;
+	}
+
 	rc = ipmi_send(ipmi, netfn, cmd, req_buf, req_len);
 	if (rc)
-		return rc;
+		goto out;
 
 	pollfds[0].fd = ipmi->fd;
 	pollfds[0].events = POLLIN;
@@ -132,11 +142,13 @@ int ipmi_transaction(struct ipmi *ipmi, uint8_t netfn, uint8_t cmd,
 		if (rc == 0) {
 			pb_log("IPMI: timeout waiting for response "
 					"(netfn %d, cmd %d)\n", netfn, cmd);
+			rc = -1;
 			break;
 		}
 
 		if (!(pollfds[0].revents & POLLIN)) {
 			pb_log("IPMI: unexpected fd status from poll?\n");
+			rc = -1;
 			break;
 		}
 
@@ -156,17 +168,23 @@ int ipmi_transaction(struct ipmi *ipmi, uint8_t netfn, uint8_t cmd,
 				expired_ms = (delta.tv_sec * 1000) +
 						(delta.tv_usec / 1000);
 
-				if (expired_ms >= timeout_ms)
+				if (expired_ms >= timeout_ms) {
+					rc = -1;
 					break;
+				}
 			}
 		} else {
 			pb_debug("IPMI: netfn(%x->%x), cmd(%x->%x)\n",
 					netfn, resp_netfn, cmd, resp_cmd);
-			return 0;
+			rc = 0;
+			goto out;
 		}
 	}
 
-	return -1;
+out:
+	lock.l_type = F_UNLCK;
+	fcntl(ipmi->fd, F_SETLKW, &lock);
+	return rc ? -1 : 0;
 }
 
 static int ipmi_destroy(void *p)