liblog: Instrument logging of logd write drops

LOCAL_PATH := $(my-dir)

include $(CLEAR_VARS)

liblog_cflags := $(shell sed -n 's/^\([0-9]*\)[ \t]*liblog[ \t].*/-DLIBLOG_LOG_TAG=\1/p' $(LOCAL_PATH)/event.logtags)

ifneq ($(TARGET_USES_LOGD),false)

liblog_sources := logd_write.c

else

        uio.c

endif

liblog_host_sources := $(liblog_sources) fake_log_device.c

liblog_host_sources := $(liblog_sources) fake_log_device.c event.logtags

liblog_target_sources := $(liblog_sources) log_time.cpp log_is_loggable.c

ifneq ($(TARGET_USES_LOGD),false)

liblog_target_sources += log_read.c

# ========================================================

LOCAL_MODULE := liblog

LOCAL_SRC_FILES := $(liblog_host_sources)

LOCAL_CFLAGS := -DFAKE_LOG_DEVICE=1 -Werror

LOCAL_CFLAGS := -DFAKE_LOG_DEVICE=1 -Werror $(liblog_cflags)

LOCAL_MULTILIB := both

include $(BUILD_HOST_STATIC_LIBRARY)

include $(CLEAR_VARS)

LOCAL_MODULE := liblog

LOCAL_SRC_FILES := $(liblog_target_sources)

LOCAL_CFLAGS := -Werror

LOCAL_CFLAGS := -Werror $(liblog_cflags)

include $(BUILD_STATIC_LIBRARY)

include $(CLEAR_VARS)

LOCAL_MODULE := liblog

LOCAL_WHOLE_STATIC_LIBRARIES := liblog

LOCAL_CFLAGS := -Werror

LOCAL_CFLAGS := -Werror $(liblog_cflags)

include $(BUILD_SHARED_LIBRARY)

include $(call first-makefiles-under,$(LOCAL_PATH))

       when  opening  the  sub-log.    It  is  recommended  to  open  the  log

       ANDROID_LOG_RDONLY in these cases.

ERRORS

       If messages fail, a negative error code will be returned to the caller.

       The -ENOTCONN return code indicates that the logger daemon is stopped.

       The  -EBADF return code indicates that the log access point can not be

       opened, or the log buffer id is out of range.

       For the  -EAGAIN  return code,  this means that the logging message was

       temporarily backed-up either because of Denial Of Service (DOS) logging

       pressure from some chatty application or service in the Android system,

       or if too small of a value is set in /proc/sys/net/unix/max_dgram_qlen.

       To aid in diagnosing the occurence of this,  a binary event from liblog

       will be sent to the  log  daemon  once a  new  message  can get through

       indicating how many  messages were  dropped  as a result.   Please take

       action to resolve the structural problems at the source.

       It is generally not advised for the caller to retry the  -EAGAIN return

       code as  this  will  only  make the  problem(s)  worse  and  cause your

       application to temporarily drop to the  logger daemon  priority,  BATCH

       scheduling policy and background task cgroup. If you require a group of

       messages to be passed atomically,  merge  them  into  one  message with

       embedded newlines to the maximum length LOGGER_ENTRY_MAX_PAYLOAD.

       Other return codes  from  writing operation can be returned.  Since the

       library retries on EINTR, -EINTR should never be returned.

SEE ALSO

       syslogd(8)

# The entries in this file map a sparse set of log tag numbers to tag names.

# This is installed on the device, in /system/etc, and parsed by logcat.

#

# Tag numbers are decimal integers, from 0 to 2^31.  (Let's leave the

# negative values alone for now.)

#

# Tag names are one or more ASCII letters and numbers or underscores, i.e.

# "[A-Z][a-z][0-9]_".  Do not include spaces or punctuation (the former

# impacts log readability, the latter makes regex searches more annoying).

#

# Tag numbers and names are separated by whitespace.  Blank lines and lines

# starting with '#' are ignored.

#

# Optionally, after the tag names can be put a description for the value(s)

# of the tag. Description are in the format

#    (<name>|data type[|data unit])

# Multiple values are separated by commas.

#

# The data type is a number from the following values:

# 1: int

# 2: long

# 3: string

# 4: list

#

# The data unit is a number taken from the following list:

# 1: Number of objects

# 2: Number of bytes

# 3: Number of milliseconds

# 4: Number of allocations

# 5: Id

# 6: Percent

# Default value for data of type int/long is 2 (bytes).

#

# TODO: generate ".java" and ".h" files with integer constants from this file.

1005  liblog (dropped|1)

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

#include <endian.h>

#include <errno.h>

#include <fcntl.h>

#if !defined(_WIN32)

#include <pthread.h>

#endif

#include <stdarg.h>

#include <stdatomic.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

    size_t i, payload_size;

    static uid_t last_uid = AID_ROOT; /* logd *always* starts up as AID_ROOT */

    static pid_t last_pid = (pid_t) -1;

    static atomic_int_fast32_t dropped;

    if (last_uid == AID_ROOT) { /* have we called to get the UID yet? */

        last_uid = getuid();

    pmsg_header.uid = last_uid;

    pmsg_header.pid = last_pid;

    header.id = log_id;

    header.tid = gettid();

    header.realtime.tv_sec = ts.tv_sec;

    header.realtime.tv_nsec = ts.tv_nsec;

    newVec[1].iov_base   = (unsigned char *) &header;

    newVec[1].iov_len    = sizeof(header);

    if (logd_fd > 0) {

        int32_t snapshot = atomic_exchange_explicit(&dropped, 0, memory_order_relaxed);

        if (snapshot) {

            android_log_event_int_t buffer;

            header.id = LOG_ID_EVENTS;

            buffer.header.tag = htole32(LIBLOG_LOG_TAG);

            buffer.payload.type = EVENT_TYPE_INT;

            buffer.payload.data = htole32(snapshot);

            newVec[2].iov_base = &buffer;

            newVec[2].iov_len  = sizeof(buffer);

            ret = TEMP_FAILURE_RETRY(writev(logd_fd, newVec + 1, 2));

            if (ret != (ssize_t)(sizeof(header) + sizeof(buffer))) {

                atomic_fetch_add_explicit(&dropped, snapshot, memory_order_relaxed);

            }

        }

    }

    header.id = log_id;

    for (payload_size = 0, i = header_length; i < nr + header_length; i++) {

        newVec[i].iov_base = vec[i - header_length].iov_base;

        payload_size += newVec[i].iov_len = vec[i - header_length].iov_len;

    if (ret > (ssize_t)sizeof(header)) {

        ret -= sizeof(header);

    } else if (ret == -EAGAIN) {

        atomic_fetch_add_explicit(&dropped, 1, memory_order_relaxed);

    }

#endif