liblog: use a blocking socket for sending messages to logd
liblog uses a non-blocking socket for sending messages to logd as a
performance/reliability trade-off, favoring not blocking processes
when they log over reliably tracking all logs.
This change asserts that the above is the wrong trade-off: that log
relability is more important than slight delays when logging. Further
points to consider:
1) The new logd implementation without chatty has lower latency and
less variance in its ::Log() function.
2) liblog also writes to /dev/pmsg0 and this call is already blocking.
3) Logging is already expensive and excess spam must be eliminated
regardless.
Bug: 151654749
Bug: 155922578
Bug: 160314220
Test: No messages are dropped by this socket
Change-Id: I163b7d51aa73a10978850f1868cb9fc4bf9ead1b
diff --git a/liblog/logd_writer.cpp b/liblog/logd_writer.cpp
index a230749..f5d19ca 100644
--- a/liblog/logd_writer.cpp
+++ b/liblog/logd_writer.cpp
@@ -59,8 +59,7 @@
return;
}
- int new_socket =
- TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0));
+ int new_socket = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0));
if (new_socket <= 0) {
return;
}
@@ -91,8 +90,6 @@
struct iovec newVec[nr + headerLength];
android_log_header_t header;
size_t i, payloadSize;
- static atomic_int dropped;
- static atomic_int droppedSecurity;
GetSocket();
@@ -110,6 +107,7 @@
return 0;
}
+ header.id = logId;
header.tid = gettid();
header.realtime.tv_sec = ts->tv_sec;
header.realtime.tv_nsec = ts->tv_nsec;
@@ -117,44 +115,6 @@
newVec[0].iov_base = (unsigned char*)&header;
newVec[0].iov_len = sizeof(header);
- int32_t snapshot = atomic_exchange_explicit(&droppedSecurity, 0, memory_order_relaxed);
- if (snapshot) {
- android_log_event_int_t buffer;
-
- header.id = LOG_ID_SECURITY;
- buffer.header.tag = LIBLOG_LOG_TAG;
- buffer.payload.type = EVENT_TYPE_INT;
- buffer.payload.data = snapshot;
-
- newVec[headerLength].iov_base = &buffer;
- newVec[headerLength].iov_len = sizeof(buffer);
-
- ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, 2));
- if (ret != (ssize_t)(sizeof(header) + sizeof(buffer))) {
- atomic_fetch_add_explicit(&droppedSecurity, snapshot, memory_order_relaxed);
- }
- }
- snapshot = atomic_exchange_explicit(&dropped, 0, memory_order_relaxed);
- if (snapshot && __android_log_is_loggable_len(ANDROID_LOG_INFO, "liblog", strlen("liblog"),
- ANDROID_LOG_VERBOSE)) {
- android_log_event_int_t buffer;
-
- header.id = LOG_ID_EVENTS;
- buffer.header.tag = LIBLOG_LOG_TAG;
- buffer.payload.type = EVENT_TYPE_INT;
- buffer.payload.data = snapshot;
-
- newVec[headerLength].iov_base = &buffer;
- newVec[headerLength].iov_len = sizeof(buffer);
-
- ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, 2));
- if (ret != (ssize_t)(sizeof(header) + sizeof(buffer))) {
- atomic_fetch_add_explicit(&dropped, snapshot, memory_order_relaxed);
- }
- }
-
- header.id = logId;
-
for (payloadSize = 0, i = headerLength; i < nr + headerLength; i++) {
newVec[i].iov_base = vec[i - headerLength].iov_base;
payloadSize += newVec[i].iov_len = vec[i - headerLength].iov_len;
@@ -168,11 +128,8 @@
}
}
- // The write below could be lost, but will never block.
- // EAGAIN occurs if logd is overloaded, other errors indicate that something went wrong with
- // the connection, so we reset it and try again.
ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, i));
- if (ret < 0 && errno != EAGAIN) {
+ if (ret < 0) {
LogdConnect();
ret = TEMP_FAILURE_RETRY(writev(logd_socket, newVec, i));
@@ -182,14 +139,5 @@
ret = -errno;
}
- if (ret > (ssize_t)sizeof(header)) {
- ret -= sizeof(header);
- } else if (ret < 0) {
- atomic_fetch_add_explicit(&dropped, 1, memory_order_relaxed);
- if (logId == LOG_ID_SECURITY) {
- atomic_fetch_add_explicit(&droppedSecurity, 1, memory_order_relaxed);
- }
- }
-
return ret;
}