android log丢失（三）动态切换logd机制和kernel机制
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之前我们分析了如何修改版本使log机制变成kernel的log机制。这篇博客我们继续修改可以动态切换，这样方便平时log丢失时调试。
我们先来看liblog库的编译mk文件，这个文件中主要修改了对使用使用logd 使用不同文件进行编译这块做了修改，增加了log_write_common.c 和log_read_common.c两个通用文件。
## Copyright (C) 2008-2014 The Android Open Source Project## Licensed under the Apache License, Version 2.0 (the "License");# you may not use this file except in compliance with the License.# You may obtain a copy of the License at## http://www.apache.org/licenses/LICENSE-2.0## Unless required by applicable law or agreed to in writing, software# distributed under the License is distributed on an "AS IS" BASIS,# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.# See the License for the specific language governing permissions and# limitations under the License.#LOCAL_PATH := $(my-dir)include $(CLEAR_VARS)# This is what we want to do:# liblog_cflags := $(shell \# sed -n \# 's/^\([0-9]*\)[ \t]*liblog[ \t].*/-DLIBLOG_LOG_TAG=\1/p' \# $(LOCAL_PATH)/event.logtags)# so make sure we do not regret hard-coding it as follows:liblog_cflags := -DLIBLOG_LOG_TAG=1005#ifneq ($(TARGET_USES_LOGD),false)//注释了 不需要区分使用使用logd#liblog_sources := logd_write.c log_event_write.c#else#liblog_sources := logd_write_kern.c log_event_write.c#endifliblog_sources := log_write_common.c log_event_write.c//增加log_write_common.c # some files must not be compiled when building against Mingw# they correspond to features not used by our host development tools# which are also hard or even impossible to port to native Win32ifeq ($(strip $(USE_MINGW)),) liblog_sources += \ event_tag_map.celse liblog_sources += \ uio.cendifliblog_host_sources := $(liblog_sources) fake_log_device.c event.logtagsliblog_target_sources := $(liblog_sources) log_time.cpp log_is_loggable.cifeq ($(strip $(USE_MINGW)),)liblog_target_sources += logprint.cendif#ifneq ($(TARGET_USES_LOGD),false)//注释了，不用区分是否使用logd#liblog_target_sources += log_read.c#else#liblog_target_sources += log_read_kern.c#endifliblog_target_sources += log_read_common.c//增加log_read_common.c# Shared and static library for host# ========================================================LOCAL_MODULE := liblogLOCAL_SRC_FILES := $(liblog_host_sources)LOCAL_CFLAGS := -DFAKE_LOG_DEVICE=1 -Werror $(liblog_cflags)LOCAL_MULTILIB := bothinclude $(BUILD_HOST_STATIC_LIBRARY)include $(CLEAR_VARS)LOCAL_MODULE := liblogLOCAL_WHOLE_STATIC_LIBRARIES := liblogifeq ($(strip $(HOST_OS)),linux)LOCAL_LDLIBS := -lrtendifLOCAL_MULTILIB := bothinclude $(BUILD_HOST_SHARED_LIBRARY)# Shared and static library for target# ========================================================include $(CLEAR_VARS)LOCAL_MODULE := liblogLOCAL_SRC_FILES := $(liblog_target_sources)LOCAL_CFLAGS := -Werror $(liblog_cflags)include $(BUILD_STATIC_LIBRARY)include $(CLEAR_VARS)LOCAL_MODULE := liblogLOCAL_WHOLE_STATIC_LIBRARIES := liblogLOCAL_CFLAGS := -Werror $(liblog_cflags)# TODO: This is to work around b/19059885. Remove after root cause is fixedLOCAL_LDFLAGS_arm := -Wl,--hash-style=bothinclude $(BUILD_SHARED_LIBRARY)include $(call first-makefiles-under,$(LOCAL_PATH))
我们先来看log_read_common.c文件，这样主要就是将原来的logd_write.c 和logd_write_kern.c 文件进行合并。一些对外的接口，统一使用use_logd这个全局变量来控制，选择logd的函数，还是kernel的函数（logd的函数和kernel的函数就是static函数了，不用对外）。另外在__write_to_log_init函数中，第一次初始化的使用，先看system/etc/disable_logd是否有这样一个文件，有就将use_logd为0，代表使用kernel机制。
/* * Copyright (C) 2007-2014 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */#if (FAKE_LOG_DEVICE == 0)#include <endian.h>#endif#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>#include <sys/stat.h>#include <sys/types.h>#if (FAKE_LOG_DEVICE == 0)#include <sys/socket.h>#include <sys/un.h>#endif#include <time.h>#include <unistd.h>#ifdef __BIONIC__#include <android/set_abort_message.h>#endif#include <log/log.h>#include <log/logd.h>#include <log/logger.h>#include <log/log_read.h>#include <private/android_filesystem_config.h>#include <private/android_logger.h>#define LOGGER_LOG_MAIN "log/main"#define LOGGER_LOG_RADIO "log/radio"#define LOGGER_LOG_EVENTS "log/events"#define LOGGER_LOG_SYSTEM "log/system"#define LOG_BUF_SIZE 1024#if FAKE_LOG_DEVICE/* This will be defined when building for the host. */#include "fake_log_device.h"#endif#define log_open(pathname, flags) open(pathname, (flags) | O_CLOEXEC)#define log_writev(filedes, vector, count) writev(filedes, vector, count)#define log_close(filedes) close(filedes)static int __write_to_log_init(log_id_t, struct iovec *vec, size_t nr);static int (*write_to_log)(log_id_t, struct iovec *vec, size_t nr) = __write_to_log_init;#if !defined(_WIN32)static pthread_mutex_t log_init_lock = PTHREAD_MUTEX_INITIALIZER;#endif#ifndef __unused#define __unused __attribute__((__unused__))#endifstatic int8_t use_logd = 1;//做区分#if FAKE_LOG_DEVICEstatic int log_fds_fake[(int)LOG_ID_MAX] = { -1, -1, -1, -1, -1 };#elsestatic int logd_fd = -1;static int pstore_fd = -1;#endifstatic int log_fds_kernel[(int)LOG_ID_MAX] = { -1, -1, -1, -1 };/* * This is used by the C++ code to decide if it should write logs through * the C code. Basically, if /dev/socket/logd is available, we're running in * the simulator rather than a desktop tool and want to use the device. */static enum { kLogUninitialized, kLogNotAvailable, kLogAvailable} g_log_status = kLogUninitialized;static int __android_log_dev_available_logd(void){ if (g_log_status == kLogUninitialized) { if (access("/dev/socket/logdw", W_OK) == 0) g_log_status = kLogAvailable; else g_log_status = kLogNotAvailable; } return (g_log_status == kLogAvailable);}static int __android_log_dev_available_kernel(void){ if (g_log_status == kLogUninitialized) { if (access("/dev/"LOGGER_LOG_MAIN, W_OK) == 0) g_log_status = kLogAvailable; else g_log_status = kLogNotAvailable; } return (g_log_status == kLogAvailable);}int __android_log_dev_available(void){ if (use_logd) { return __android_log_dev_available_logd(); } else { return __android_log_dev_available_kernel(); }}/* log_init_lock assumed */static int __write_to_log_initialize(){ int i, ret = 0;#if FAKE_LOG_DEVICE for (i = 0; i < LOG_ID_MAX; i++) { char buf[sizeof("/dev/log_system")]; snprintf(buf, sizeof(buf), "/dev/log_%s", android_log_id_to_name(i)); log_fds_fake[i] = fakeLogOpen(buf, O_WRONLY); }#else if (pstore_fd < 0) { pstore_fd = TEMP_FAILURE_RETRY(open("/dev/pmsg0", O_WRONLY)); } if (logd_fd < 0) { i = TEMP_FAILURE_RETRY(socket(PF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0)); if (i < 0) { ret = -errno; } else if (TEMP_FAILURE_RETRY(fcntl(i, F_SETFL, O_NONBLOCK)) < 0) { ret = -errno; close(i); } else { struct sockaddr_un un; memset(&un, 0, sizeof(struct sockaddr_un)); un.sun_family = AF_UNIX; strcpy(un.sun_path, "/dev/socket/logdw"); if (TEMP_FAILURE_RETRY(connect(i, (struct sockaddr *)&un, sizeof(struct sockaddr_un))) < 0) { ret = -errno; close(i); } else { logd_fd = i; } } }#endif return ret;}static int __write_to_log_daemon(log_id_t log_id, struct iovec *vec, size_t nr){ ssize_t ret;#if FAKE_LOG_DEVICE int log_fd; if (/*(int)log_id >= 0 &&*/ (int)log_id < (int)LOG_ID_MAX) { log_fd = log_fds_fake[(int)log_id]; } else { return -EBADF; } do { ret = fakeLogWritev(log_fd, vec, nr); if (ret < 0) { ret = -errno; } } while (ret == -EINTR);#else static const unsigned header_length = 2; struct iovec newVec[nr + header_length]; android_log_header_t header; android_pmsg_log_header_t pmsg_header; struct timespec ts; 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 (!nr) { return -EINVAL; } if (last_uid == AID_ROOT) { /* have we called to get the UID yet? */ last_uid = getuid(); } if (last_pid == (pid_t) -1) { last_pid = getpid(); } /* * struct { * // what we provide to pstore * android_pmsg_log_header_t pmsg_header; * // what we provide to socket * android_log_header_t header; * // caller provides * union { * struct { * char prio; * char payload[]; * } string; * struct { * uint32_t tag * char payload[]; * } binary; * }; * }; */ clock_gettime(CLOCK_REALTIME, &ts); pmsg_header.magic = LOGGER_MAGIC; pmsg_header.len = sizeof(pmsg_header) + sizeof(header); pmsg_header.uid = last_uid; pmsg_header.pid = last_pid; header.tid = gettid(); header.realtime.tv_sec = ts.tv_sec; header.realtime.tv_nsec = ts.tv_nsec; newVec[0].iov_base = (unsigned char *) &pmsg_header; newVec[0].iov_len = sizeof(pmsg_header); 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 (payload_size > LOGGER_ENTRY_MAX_PAYLOAD) { newVec[i].iov_len -= payload_size - LOGGER_ENTRY_MAX_PAYLOAD; if (newVec[i].iov_len) { ++i; } payload_size = LOGGER_ENTRY_MAX_PAYLOAD; break; } } pmsg_header.len += payload_size; if (pstore_fd >= 0) { TEMP_FAILURE_RETRY(writev(pstore_fd, newVec, i)); } if (last_uid == AID_LOGD) { /* logd, after initialization and priv drop */ /* * ignore log messages we send to ourself (logd). * Such log messages are often generated by libraries we depend on * which use standard Android logging. */ return 0; } if (logd_fd < 0) { return -EBADF; } /* * The write below could be lost, but will never block. * * To logd, we drop the pmsg_header * * ENOTCONN occurs if logd dies. * EAGAIN occurs if logd is overloaded. */ ret = TEMP_FAILURE_RETRY(writev(logd_fd, newVec + 1, i - 1)); if (ret < 0) { ret = -errno; if (ret == -ENOTCONN) {#if !defined(_WIN32) pthread_mutex_lock(&log_init_lock);#endif close(logd_fd); logd_fd = -1; ret = __write_to_log_initialize();#if !defined(_WIN32) pthread_mutex_unlock(&log_init_lock);#endif if (ret < 0) { return ret; } ret = TEMP_FAILURE_RETRY(writev(logd_fd, newVec + 1, i - 1)); if (ret < 0) { ret = -errno; } } } if (ret > (ssize_t)sizeof(header)) { ret -= sizeof(header); } else if (ret == -EAGAIN) { atomic_fetch_add_explicit(&dropped, 1, memory_order_relaxed); }#endif return ret;}#if FAKE_LOG_DEVICEstatic const char *LOG_NAME[LOG_ID_MAX] = { [LOG_ID_MAIN] = "main", [LOG_ID_RADIO] = "radio", [LOG_ID_EVENTS] = "events", [LOG_ID_SYSTEM] = "system", [LOG_ID_CRASH] = "crash", [LOG_ID_KERNEL] = "kernel",};const char *android_log_id_to_name(log_id_t log_id){ if (log_id >= LOG_ID_MAX) { log_id = LOG_ID_MAIN; } return LOG_NAME[log_id];}#endifstatic int __write_to_log_init_logd(log_id_t log_id, struct iovec *vec, size_t nr){#if !defined(_WIN32) pthread_mutex_lock(&log_init_lock);#endif if (write_to_log == __write_to_log_init) { int ret; ret = __write_to_log_initialize(); if (ret < 0) {#if !defined(_WIN32) pthread_mutex_unlock(&log_init_lock);#endif#if (FAKE_LOG_DEVICE == 0) if (pstore_fd >= 0) { __write_to_log_daemon(log_id, vec, nr); }#endif return ret; } write_to_log = __write_to_log_daemon; }#if !defined(_WIN32) pthread_mutex_unlock(&log_init_lock);#endif return write_to_log(log_id, vec, nr);}static int __write_to_log_null(log_id_t log_fd __unused, struct iovec *vec __unused, size_t nr __unused){ return -1;}static int __write_to_log_kernel(log_id_t log_id, struct iovec *vec, size_t nr){ ssize_t ret; int log_fd; if (/*(int)log_id >= 0 &&*/ (int)log_id < (int)LOG_ID_MAX) { if (log_id == LOG_ID_CRASH) { log_id = LOG_ID_MAIN; } log_fd = log_fds_kernel[(int)log_id]; } else { return -EBADF; } do { ret = log_writev(log_fd, vec, nr); if (ret < 0) { ret = -errno; } } while (ret == -EINTR); return ret;}static int __write_to_log_init_kernel(log_id_t log_id, struct iovec *vec, size_t nr){ pthread_mutex_lock(&log_init_lock); if (write_to_log == __write_to_log_init) { log_fds_kernel[LOG_ID_MAIN] = log_open("/dev/"LOGGER_LOG_MAIN, O_WRONLY); log_fds_kernel[LOG_ID_RADIO] = log_open("/dev/"LOGGER_LOG_RADIO, O_WRONLY); log_fds_kernel[LOG_ID_EVENTS] = log_open("/dev/"LOGGER_LOG_EVENTS, O_WRONLY); log_fds_kernel[LOG_ID_SYSTEM] = log_open("/dev/"LOGGER_LOG_SYSTEM, O_WRONLY); write_to_log = __write_to_log_kernel; if (log_fds_kernel[LOG_ID_MAIN] < 0 || log_fds_kernel[LOG_ID_RADIO] < 0 || log_fds_kernel[LOG_ID_EVENTS] < 0) { log_close(log_fds_kernel[LOG_ID_MAIN]); log_close(log_fds_kernel[LOG_ID_RADIO]); log_close(log_fds_kernel[LOG_ID_EVENTS]); log_fds_kernel[LOG_ID_MAIN] = -1; log_fds_kernel[LOG_ID_RADIO] = -1; log_fds_kernel[LOG_ID_EVENTS] = -1; write_to_log = __write_to_log_null; } if (log_fds_kernel[LOG_ID_SYSTEM] < 0) { log_fds_kernel[LOG_ID_SYSTEM] = log_fds_kernel[LOG_ID_MAIN]; } } pthread_mutex_unlock(&log_init_lock); return write_to_log(log_id, vec, nr);}static int __write_to_log_init(log_id_t log_id, struct iovec *vec, size_t nr) {#if (FAKE_LOG_DEVICE == 0) int fd; fd = open("system/etc/disable_logd", O_RDONLY);//是否有disable_logd文件 if (fd > 0) { use_logd = 0; close(fd); }#endif if(use_logd) { return __write_to_log_init_logd(log_id, vec, nr); } else { return __write_to_log_init_kernel(log_id, vec, nr); }}int __android_log_write(int prio, const char *tag, const char *msg){ return __android_log_buf_write(LOG_ID_MAIN, prio, tag, msg);}int __android_log_buf_write(int bufID, int prio, const char *tag, const char *msg){ struct iovec vec[3]; char tmp_tag[32]; if (!tag) tag = ""; /* XXX: This needs to go! */ if ((bufID != LOG_ID_RADIO) && (!strcmp(tag, "HTC_RIL") || !strncmp(tag, "RIL", 3) || /* Any log tag with "RIL" as the prefix */ !strncmp(tag, "IMS", 3) || /* Any log tag with "IMS" as the prefix */ !strcmp(tag, "AT") || !strcmp(tag, "GSM") || !strcmp(tag, "STK") || !strcmp(tag, "CDMA") || !strcmp(tag, "PHONE") || !strcmp(tag, "SMS"))) { bufID = LOG_ID_RADIO; /* Inform third party apps/ril/radio.. to use Rlog or RLOG */ snprintf(tmp_tag, sizeof(tmp_tag), "use-Rlog/RLOG-%s", tag); tag = tmp_tag; }#if __BIONIC__ if (prio == ANDROID_LOG_FATAL) { android_set_abort_message(msg); }#endif vec[0].iov_base = (unsigned char *) &prio; vec[0].iov_len = 1; vec[1].iov_base = (void *) tag; vec[1].iov_len = strlen(tag) + 1; vec[2].iov_base = (void *) msg; vec[2].iov_len = strlen(msg) + 1; return write_to_log(bufID, vec, 3);}int __android_log_vprint(int prio, const char *tag, const char *fmt, va_list ap){ char buf[LOG_BUF_SIZE]; vsnprintf(buf, LOG_BUF_SIZE, fmt, ap); return __android_log_write(prio, tag, buf);}int __android_log_print(int prio, const char *tag, const char *fmt, ...){ va_list ap; char buf[LOG_BUF_SIZE]; va_start(ap, fmt); vsnprintf(buf, LOG_BUF_SIZE, fmt, ap); va_end(ap); return __android_log_write(prio, tag, buf);}int __android_log_buf_print(int bufID, int prio, const char *tag, const char *fmt, ...){ va_list ap; char buf[LOG_BUF_SIZE]; va_start(ap, fmt); vsnprintf(buf, LOG_BUF_SIZE, fmt, ap); va_end(ap); return __android_log_buf_write(bufID, prio, tag, buf);}void __android_log_assert(const char *cond, const char *tag, const char *fmt, ...){ char buf[LOG_BUF_SIZE]; if (fmt) { va_list ap; va_start(ap, fmt); vsnprintf(buf, LOG_BUF_SIZE, fmt, ap); va_end(ap); } else { /* Msg not provided, log condition. N.B. Do not use cond directly as * format string as it could contain spurious '%' syntax (e.g. * "%d" in "blocks%devs == 0"). */ if (cond) snprintf(buf, LOG_BUF_SIZE, "Assertion failed: %s", cond); else strcpy(buf, "Unspecified assertion failed"); } __android_log_write(ANDROID_LOG_FATAL, tag, buf); abort(); /* abort so we have a chance to debug the situation */ /* NOTREACHED */}int __android_log_bwrite(int32_t tag, const void *payload, size_t len){ struct iovec vec[2]; vec[0].iov_base = &tag; vec[0].iov_len = sizeof(tag); vec[1].iov_base = (void*)payload; vec[1].iov_len = len; return write_to_log(LOG_ID_EVENTS, vec, 2);}/* * Like __android_log_bwrite, but takes the type as well. Doesn't work * for the general case where we're generating lists of stuff, but very * handy if we just want to dump an integer into the log. */int __android_log_btwrite(int32_t tag, char type, const void *payload, size_t len){ struct iovec vec[3]; vec[0].iov_base = &tag; vec[0].iov_len = sizeof(tag); vec[1].iov_base = &type; vec[1].iov_len = sizeof(type); vec[2].iov_base = (void*)payload; vec[2].iov_len = len; return write_to_log(LOG_ID_EVENTS, vec, 3);}/* * Like __android_log_bwrite, but used for writing strings to the * event log. */int __android_log_bswrite(int32_t tag, const char *payload){ struct iovec vec[4]; char type = EVENT_TYPE_STRING; uint32_t len = strlen(payload); vec[0].iov_base = &tag; vec[0].iov_len = sizeof(tag); vec[1].iov_base = &type; vec[1].iov_len = sizeof(type); vec[2].iov_base = &len; vec[2].iov_len = sizeof(len); vec[3].iov_base = (void*)payload; vec[3].iov_len = len; return write_to_log(LOG_ID_EVENTS, vec, 4);}另外一个就是log_read_common.c文件，将log_read.c和log_read_kern.c合并。这样文件稍微复杂一点，因为在log_read.c和log_read_kern.c中都使用了struct logger_list 和struct logger结构体而且不一样，这样我们将共同部分做了一个基类的struct logger_list 和struct logger结构体。而在合并文件中定义了struct logger_list_logd struct logger_list_kernel结构体，将其基类放在第一个变量base中。而使用指针时，对外返回的指针强制转成基类，进入的指针强制转到相关的子类。因为基类的数据结构在子类结构体中是第一个，因此子类指针强转成父类，也是能正确调用到父类的变量的。
还有我们也是用use_logd这个全局变量来控制log机制的，并且定义了一个对外的函数set_uselogd. 因为使用read这块是在logcat进程中使用的，我们需要在logcat中调用。
/*** Copyright 2013-2014, The Android Open Source Project**** Licensed under the Apache License, Version 2.0 (the "License");** you may not use this file except in compliance with the License.** You may obtain a copy of the License at**** http://www.apache.org/licenses/LICENSE-2.0**** Unless required by applicable law or agreed to in writing, software** distributed under the License is distributed on an "AS IS" BASIS,** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.** See the License for the specific language governing permissions and** limitations under the License.*/#define _GNU_SOURCE /* asprintf for x86 host */#include <errno.h>#include <fcntl.h>#include <inttypes.h>#include <poll.h>#include <signal.h>#include <stdbool.h>#include <stddef.h>#define NOMINMAX /* for windows to suppress definition of min in stdlib.h */#include <stdlib.h>#include <string.h>#include <sys/cdefs.h>#include <sys/ioctl.h>#include <unistd.h>#include <string.h>#include <stdio.h>#include <cutils/list.h>#include <cutils/sockets.h>#include <log/log.h>#include <log/logger.h>#include <private/android_filesystem_config.h>#include <private/android_logger.h>#include <cutils/sockets.h>#define __LOGGERIO 0xAE#define LOGGER_GET_LOG_BUF_SIZE _IO(__LOGGERIO, 1) /* size of log */#define LOGGER_GET_LOG_LEN _IO(__LOGGERIO, 2) /* used log len */#define LOGGER_GET_NEXT_ENTRY_LEN _IO(__LOGGERIO, 3) /* next entry len */#define LOGGER_FLUSH_LOG _IO(__LOGGERIO, 4) /* flush log */#define LOGGER_GET_VERSION _IO(__LOGGERIO, 5) /* abi version */#define LOGGER_SET_VERSION _IO(__LOGGERIO, 6) /* abi version */#define LOG_FILE_DIR "/dev/log/"/* timeout in milliseconds */#define LOG_TIMEOUT_FLUSH 5#define LOG_TIMEOUT_NEVER -1/* branchless on many architectures. */#define min(x,y) ((y) ^ (((x) ^ (y)) & -((x) < (y))))#if (defined(USE_MINGW) || defined(HAVE_WINSOCK))#define WEAK static#else#define WEAK __attribute__((weak))#endif#ifndef __unused#define __unused __attribute__((unused))#endifstatic int8_t use_logd = 1;//版本控制void set_uselogd(int8_t uselogd) {//对外函数 use_logd = uselogd;}/* Private copy of ../libcutils/socket_local_client.c prevent library loops */#ifdef HAVE_WINSOCKint WEAK socket_local_client(const char *name, int namespaceId, int type){ errno = ENOSYS; return -ENOSYS;}#else /* !HAVE_WINSOCK */#include <sys/socket.h>#include <sys/un.h>#include <sys/select.h>#include <sys/types.h>/* Private copy of ../libcutils/socket_local.h prevent library loops */#define FILESYSTEM_SOCKET_PREFIX "/tmp/"#define ANDROID_RESERVED_SOCKET_PREFIX "/dev/socket/"/* End of ../libcutils/socket_local.h */#define LISTEN_BACKLOG 4/* Documented in header file. */int WEAK socket_make_sockaddr_un(const char *name, int namespaceId, struct sockaddr_un *p_addr, socklen_t *alen){ memset (p_addr, 0, sizeof (*p_addr)); size_t namelen; switch (namespaceId) { case ANDROID_SOCKET_NAMESPACE_ABSTRACT:#if defined(__linux__) namelen = strlen(name); /* Test with length +1 for the *initial* '\0'. */ if ((namelen + 1) > sizeof(p_addr->sun_path)) { goto error; } /* * Note: The path in this case is *not* supposed to be * '\0'-terminated. ("man 7 unix" for the gory details.) */ p_addr->sun_path[0] = 0; memcpy(p_addr->sun_path + 1, name, namelen);#else /* this OS doesn't have the Linux abstract namespace */ namelen = strlen(name) + strlen(FILESYSTEM_SOCKET_PREFIX); /* unix_path_max appears to be missing on linux */ if (namelen > sizeof(*p_addr) - offsetof(struct sockaddr_un, sun_path) - 1) { goto error; } strcpy(p_addr->sun_path, FILESYSTEM_SOCKET_PREFIX); strcat(p_addr->sun_path, name);#endif break; case ANDROID_SOCKET_NAMESPACE_RESERVED: namelen = strlen(name) + strlen(ANDROID_RESERVED_SOCKET_PREFIX); /* unix_path_max appears to be missing on linux */ if (namelen > sizeof(*p_addr) - offsetof(struct sockaddr_un, sun_path) - 1) { goto error; } strcpy(p_addr->sun_path, ANDROID_RESERVED_SOCKET_PREFIX); strcat(p_addr->sun_path, name); break; case ANDROID_SOCKET_NAMESPACE_FILESYSTEM: namelen = strlen(name); /* unix_path_max appears to be missing on linux */ if (namelen > sizeof(*p_addr) - offsetof(struct sockaddr_un, sun_path) - 1) { goto error; } strcpy(p_addr->sun_path, name); break; default: /* invalid namespace id */ return -1; } p_addr->sun_family = AF_LOCAL; *alen = namelen + offsetof(struct sockaddr_un, sun_path) + 1; return 0;error: return -1;}/** * connect to peer named "name" on fd * returns same fd or -1 on error. * fd is not closed on error. that's your job. * * Used by AndroidSocketImpl */int WEAK socket_local_client_connect(int fd, const char *name, int namespaceId, int type __unused){ struct sockaddr_un addr; socklen_t alen; int err; err = socket_make_sockaddr_un(name, namespaceId, &addr, &alen); if (err < 0) { goto error; } if(connect(fd, (struct sockaddr *) &addr, alen) < 0) { goto error; } return fd;error: return -1;}/** * connect to peer named "name" * returns fd or -1 on error */int WEAK socket_local_client(const char *name, int namespaceId, int type){ int s; s = socket(AF_LOCAL, type, 0); if(s < 0) return -1; if ( 0 > socket_local_client_connect(s, name, namespaceId, type)) { close(s); return -1; } return s;}#endif /* !HAVE_WINSOCK *//* End of ../libcutils/socket_local_client.c */#define logger_for_each(logger, logger_list) \ for (logger = node_to_item((logger_list)->node.next, struct logger, node); \ logger != node_to_item(&(logger_list)->node, struct logger, node); \ logger = node_to_item((logger)->node.next, struct logger, node))#ifndef __unused#define __unused __attribute__((unused))#endif/* In the future, we would like to make this list extensible */static const char *LOG_NAME[LOG_ID_MAX] = { [LOG_ID_MAIN] = "main", [LOG_ID_RADIO] = "radio", [LOG_ID_EVENTS] = "events", [LOG_ID_SYSTEM] = "system", [LOG_ID_CRASH] = "crash", [LOG_ID_KERNEL] = "kernel",};const char *android_log_id_to_name(log_id_t log_id){ if (log_id >= LOG_ID_MAX) { log_id = LOG_ID_MAIN; } return LOG_NAME[log_id];}static int accessmode(int mode){ if ((mode & ANDROID_LOG_ACCMODE) == ANDROID_LOG_WRONLY) { return W_OK; } if ((mode & ANDROID_LOG_ACCMODE) == ANDROID_LOG_RDWR) { return R_OK | W_OK; } return R_OK;}/* repeated fragment */static int check_allocate_accessible(char **n, const char *b, int mode){ *n = NULL; if (!b) { return -EINVAL; } asprintf(n, LOG_FILE_DIR "%s", b); if (!*n) { return -1; } return access(*n, accessmode(mode));}log_id_t android_name_to_log_id_logd(const char *logName){ const char *b; int ret; if (!logName) { return -1; /* NB: log_id_t is unsigned */ } b = strrchr(logName, '/'); if (!b) { b = logName; } else { ++b; } for(ret = LOG_ID_MIN; ret < LOG_ID_MAX; ++ret) { const char *l = LOG_NAME[ret]; if (l && !strcmp(b, l)) { return ret; } } return -1; /* should never happen */}log_id_t android_name_to_log_id_kernel(const char *logName){ const char *b; char *n; int ret; if (!logName) { return -1; /* NB: log_id_t is unsigned */ } b = strrchr(logName, '/'); if (!b) { b = logName; } else { ++b; } ret = check_allocate_accessible(&n, b, ANDROID_LOG_RDONLY); free(n); if (ret) { return ret; } for(ret = LOG_ID_MIN; ret < LOG_ID_MAX; ++ret) { const char *l = LOG_NAME[ret]; if (l && !strcmp(b, l)) { return ret; } } return -1; /* should never happen */}log_id_t android_name_to_log_id(const char *logName) { if (use_logd) { return android_name_to_log_id_logd(logName); } else { return android_name_to_log_id_kernel(logName); }}struct logger_list {//基类结构体 struct listnode node; int mode; unsigned int tail; pid_t pid;};struct logger_list_logd {//logd机制结构体 struct logger_list base; log_time start; int sock;};struct logger_list_kernel {//kernel机制结构体 struct logger_list base; unsigned int queued_lines; int timeout_ms; int error; bool flush; bool valid_entry; /* valiant(?) effort to deal with memory starvation */ struct log_msg entry;};struct logger { struct listnode node; struct logger_list *top; log_id_t id;};struct log_list { struct listnode node; struct log_msg entry; /* Truncated to event->len() + 1 to save space */};struct logger_kernel { struct logger base; int fd; short *revents; struct listnode log_list;};/* android_logger_alloc unimplemented, no use case *//* android_logger_free not exported */static void android_logger_free_logd(struct logger *logger){ if (!logger) { return; } list_remove(&logger->node); free(logger);}/* android_logger_alloc unimplemented, no use case *//* android_logger_free not exported */static void android_logger_free_kernel(struct logger *logger){ if (!logger) { return; } struct logger_kernel *logger_kernel = (struct logger_kernel*)logger; struct logger_list_kernel *logger_list_kernel; while (!list_empty(&logger_kernel->log_list)) { struct log_list *entry = node_to_item( list_head(&logger_kernel->log_list), struct log_list, node); list_remove(&entry->node); free(entry); logger_list_kernel = (struct logger_list_kernel *)(logger_kernel->base.top); if (logger_list_kernel->queued_lines) { logger_list_kernel->queued_lines--; } } if (logger_kernel->fd >= 0) { close(logger_kernel->fd); } list_remove(&logger_kernel->base.node); free(logger_kernel);}/* android_logger_alloc unimplemented, no use case *//* android_logger_free not exported */void android_logger_free(struct logger *logger){ if (use_logd) { android_logger_free_logd(logger); } else { android_logger_free_kernel(logger); }}/* android_logger_alloc unimplemented, no use case *//* method for getting the associated sublog id */log_id_t android_logger_get_id(struct logger *logger){ return logger->id;}/* worker for sending the command to the logger */static ssize_t send_log_msg(struct logger *logger, const char *msg, char *buf, size_t buf_size){ ssize_t ret; size_t len; char *cp; int errno_save = 0; int sock = socket_local_client("logd", ANDROID_SOCKET_NAMESPACE_RESERVED, SOCK_STREAM); if (sock < 0) { return sock; } if (msg) { snprintf(buf, buf_size, msg, logger ? logger->id : (unsigned) -1); } len = strlen(buf) + 1; ret = TEMP_FAILURE_RETRY(write(sock, buf, len)); if (ret <= 0) { goto done; } len = buf_size; cp = buf; while ((ret = TEMP_FAILURE_RETRY(read(sock, cp, len))) > 0) { struct pollfd p; if (((size_t)ret == len) || (buf_size < PAGE_SIZE)) { break; } len -= ret; cp += ret; memset(&p, 0, sizeof(p)); p.fd = sock; p.events = POLLIN; /* Give other side 20ms to refill pipe */ ret = TEMP_FAILURE_RETRY(poll(&p, 1, 20)); if (ret <= 0) { break; } if (!(p.revents & POLLIN)) { ret = 0; break; } } if (ret >= 0) { ret += buf_size - len; }done: if ((ret == -1) && errno) { errno_save = errno; } close(sock); if (errno_save) { errno = errno_save; } return ret;}/* worker for sending the command to the logger */static int logger_ioctl(struct logger *logger, int cmd, int mode){ char *n; int f, ret; struct logger_kernel* logger_kernel = (struct logger_kernel*)logger; if (!logger_kernel || !logger_kernel->base.top) { return -EFAULT; } if (((mode & ANDROID_LOG_ACCMODE) == ANDROID_LOG_RDWR) || (((mode ^ logger_kernel->base.top->mode) & ANDROID_LOG_ACCMODE) == 0)) { return ioctl(logger_kernel->fd, cmd); } /* We go here if android_logger_list_open got mode wrong for this ioctl */ ret = check_allocate_accessible(&n, android_log_id_to_name(logger_kernel->base.id), mode); if (ret) { free(n); return ret; } f = open(n, mode); free(n); if (f < 0) { return f; } ret = ioctl(f, cmd); close (f); return ret;}static int check_log_success(char *buf, ssize_t ret){ if (ret < 0) { return ret; } if (strncmp(buf, "success", 7)) { errno = EINVAL; return -1; } return 0;}/* Determine the credentials of the caller */static bool uid_has_log_permission(uid_t uid){ return (uid == AID_SYSTEM) || (uid == AID_LOG) || (uid == AID_ROOT);}static uid_t get_best_effective_uid(){ uid_t euid; uid_t uid; gid_t gid; ssize_t i; static uid_t last_uid = (uid_t) -1; if (last_uid != (uid_t) -1) { return last_uid; } uid = getuid(); if (uid_has_log_permission(uid)) { return last_uid = uid; } euid = geteuid(); if (uid_has_log_permission(euid)) { return last_uid = euid; } gid = getgid(); if (uid_has_log_permission(gid)) { return last_uid = gid; } gid = getegid(); if (uid_has_log_permission(gid)) { return last_uid = gid; } i = getgroups((size_t) 0, NULL); if (i > 0) { gid_t list[i]; getgroups(i, list); while (--i >= 0) { if (uid_has_log_permission(list[i])) { return last_uid = list[i]; } } } return last_uid = uid;}static int android_logger_clear_logd(struct logger *logger){ char buf[512]; if (logger->top->mode & ANDROID_LOG_PSTORE) { if (uid_has_log_permission(get_best_effective_uid())) { return unlink("/sys/fs/pstore/pmsg-ramoops-0"); } errno = EPERM; return -1; } return check_log_success(buf, send_log_msg(logger, "clear %d", buf, sizeof(buf)));}static int android_logger_clear_kernel(struct logger *logger){ return logger_ioctl(logger, LOGGER_FLUSH_LOG, ANDROID_LOG_WRONLY);}int android_logger_clear(struct logger *logger){ if (use_logd) { return android_logger_clear_logd(logger); } else { return android_logger_clear_kernel(logger); }}/* returns the total size of the log's ring buffer */static long android_logger_get_log_size_logd(struct logger *logger){ char buf[512]; ssize_t ret = send_log_msg(logger, "getLogSize %d", buf, sizeof(buf)); if (ret < 0) { return ret; } if ((buf[0] < '0') || ('9' < buf[0])) { return -1; } return atol(buf);}/* returns the total size of the log's ring buffer */static long android_logger_get_log_size_kernel(struct logger *logger){ return logger_ioctl(logger, LOGGER_GET_LOG_BUF_SIZE, ANDROID_LOG_RDWR);}/* returns the total size of the log's ring buffer */long android_logger_get_log_size(struct logger *logger){ if (use_logd) { return android_logger_get_log_size_logd(logger); } else { return android_logger_get_log_size_kernel(logger); }}int android_logger_set_log_size(struct logger *logger, unsigned long size){ if (use_logd) { char buf[512]; snprintf(buf, sizeof(buf), "setLogSize %d %lu", logger ? logger->id : (unsigned) -1, size); return check_log_success(buf, send_log_msg(NULL, NULL, buf, sizeof(buf))); } else { return -ENOTSUP; }}/* * returns the readable size of the log's ring buffer (that is, amount of the * log consumed) */static long android_logger_get_log_readable_size_logd(struct logger *logger){ char buf[512]; ssize_t ret = send_log_msg(logger, "getLogSizeUsed %d", buf, sizeof(buf)); if (ret < 0) { return ret; } if ((buf[0] < '0') || ('9' < buf[0])) { return -1; } return atol(buf);}/* * returns the readable size of the log's ring buffer (that is, amount of the * log consumed) */static long android_logger_get_log_readable_size_kernel(struct logger *logger){ return logger_ioctl(logger, LOGGER_GET_LOG_LEN, ANDROID_LOG_RDONLY);}/* * returns the readable size of the log's ring buffer (that is, amount of the * log consumed) */long android_logger_get_log_readable_size(struct logger *logger){ if (use_logd) { return android_logger_get_log_readable_size_logd(logger); } else { return android_logger_get_log_readable_size_kernel(logger); }}/* * returns the logger version */int android_logger_get_log_version(struct logger *logger __unused){ if (use_logd) { return 3; } else { int ret = logger_ioctl(logger, LOGGER_GET_VERSION, ANDROID_LOG_RDWR); return (ret < 0) ? 1 : ret; }}/* * returns statistics */static const char unsupported[] = "18\nNot Supported\n\f";ssize_t android_logger_get_statistics(struct logger_list *logger_list, char *buf, size_t len){ if (use_logd) { struct logger *logger; char *cp = buf; size_t remaining = len; size_t n; n = snprintf(cp, remaining, "getStatistics"); n = min(n, remaining); remaining -= n; cp += n; logger_for_each(logger, logger_list) { n = snprintf(cp, remaining, " %d", logger->id); n = min(n, remaining); remaining -= n; cp += n; } return send_log_msg(NULL, NULL, buf, len); } else { strncpy(buf, unsupported, len); return -ENOTSUP; }}ssize_t android_logger_get_prune_list(struct logger_list *logger_list __unused, char *buf, size_t len){ if (use_logd) { return send_log_msg(NULL, "getPruneList", buf, len); } else { strncpy(buf, unsupported, len); return -ENOTSUP; }}int android_logger_set_prune_list(struct logger_list *logger_list __unused, char *buf, size_t len){ if (use_logd) { const char cmd[] = "setPruneList "; const size_t cmdlen = sizeof(cmd) - 1; if (strlen(buf) > (len - cmdlen)) { return -ENOMEM; /* KISS */ } memmove(buf + cmdlen, buf, len - cmdlen); buf[len - 1] = '\0'; memcpy(buf, cmd, cmdlen); return check_log_success(buf, send_log_msg(NULL, NULL, buf, len)); } else { static const char unsupported_error[] = "Unsupported"; strncpy(buf, unsupported, len); return -ENOTSUP; }}static struct logger_list *android_logger_list_alloc_logd(int mode, unsigned int tail, pid_t pid){ struct logger_list_logd *logger_list_logd; logger_list_logd = calloc(1, sizeof(*logger_list_logd)); if (!logger_list_logd) { return NULL; } list_init(&logger_list_logd->base.node); logger_list_logd->base.mode = mode; logger_list_logd->start.tv_sec = 0; logger_list_logd->start.tv_nsec = 0; logger_list_logd->base.tail = tail; logger_list_logd->base.pid = pid; logger_list_logd->sock = -1; return (struct logger_list *)logger_list_logd;}static struct logger_list *android_logger_list_alloc_kernel(int mode, unsigned int tail, pid_t pid){ struct logger_list_kernel *logger_list_kernel; logger_list_kernel = calloc(1, sizeof(*logger_list_kernel)); if (!logger_list_kernel) { return NULL; } list_init(&logger_list_kernel->base.node); logger_list_kernel->base.mode = mode; logger_list_kernel->base.tail = tail; logger_list_kernel->base.pid = pid; return (struct logger_list *)logger_list_kernel;}struct logger_list *android_logger_list_alloc(int mode, unsigned int tail, pid_t pid){ if (use_logd) { return android_logger_list_alloc_logd(mode, tail, pid); } else { return android_logger_list_alloc_kernel(mode, tail, pid); }}static struct logger_list *android_logger_list_alloc_time_logd(int mode, log_time start, pid_t pid){ struct logger_list_logd *logger_list_logd; logger_list_logd = calloc(1, sizeof(*logger_list_logd)); if (!logger_list_logd) { return NULL; } list_init(&logger_list_logd->base.node); logger_list_logd->base.mode = mode; logger_list_logd->start = start; logger_list_logd->base.tail = 0; logger_list_logd->base.pid = pid; logger_list_logd->sock = -1; return (struct logger_list *)logger_list_logd;}static struct logger_list *android_logger_list_alloc_time_kernel(int mode, log_time start __unused, pid_t pid){ return android_logger_list_alloc(mode, 0, pid);}struct logger_list *android_logger_list_alloc_time(int mode, log_time start, pid_t pid){ if(use_logd){ return android_logger_list_alloc_time_logd(mode, start, pid); } else { return android_logger_list_alloc_time_kernel(mode, start, pid); }}/* android_logger_list_register unimplemented, no use case *//* android_logger_list_unregister unimplemented, no use case *//* Open the named log and add it to the logger list */static struct logger *android_logger_open_logd(struct logger_list *logger_list, log_id_t id){ struct logger *logger; if (!logger_list || (id >= LOG_ID_MAX)) { goto err; } logger_for_each(logger, logger_list) { if (logger->id == id) { goto ok; } } logger = calloc(1, sizeof(*logger)); if (!logger) { goto err; } logger->id = id; list_add_tail(&logger_list->node, &logger->node); logger->top = logger_list; goto ok;err: logger = NULL;ok: return logger;}/* android_logger_list_register unimplemented, no use case *//* android_logger_list_unregister unimplemented, no use case *//* Open the named log and add it to the logger list */static struct logger *android_logger_open_kernel(struct logger_list *logger_list, log_id_t id){ struct listnode *node; struct logger_kernel *logger_kernel = NULL; struct logger *logger; char *n; struct logger_list_kernel* logger_list_kernel = (struct logger_list_kernel*)logger_list; if (!logger_list || (id >= LOG_ID_MAX)) { goto err; } logger_for_each(logger, logger_list) { if (logger->id == id) { goto ok; } } logger_kernel = calloc(1, sizeof(struct logger_kernel)); if (!logger_kernel) { goto err; } if (check_allocate_accessible(&n, android_log_id_to_name(id), logger_list_kernel->base.mode)) { goto err_name; } logger_kernel->fd = open(n, logger_list_kernel->base.mode & (ANDROID_LOG_ACCMODE | ANDROID_LOG_NONBLOCK)); if (logger_kernel->fd < 0) { goto err_name; } free(n); logger_kernel->base.id = id; list_init(&logger_kernel->log_list); list_add_tail(&logger_list_kernel->base.node, &logger_kernel->base.node); logger_kernel->base.top = (struct logger_list *)logger_list_kernel; logger_list_kernel->timeout_ms = LOG_TIMEOUT_FLUSH; goto ok;err_name: free(n);err_logger: free(logger_kernel);err: logger_kernel = NULL;ok: return (struct logger *)logger_kernel;}struct logger *android_logger_open(struct logger_list *logger_list, log_id_t id){ if (use_logd) { return android_logger_open_logd(logger_list, id); } else { return android_logger_open_kernel(logger_list, id); }}/* Open the single named log and make it part of a new logger list */struct logger_list *android_logger_list_open(log_id_t id, int mode, unsigned int tail, pid_t pid){ struct logger_list *logger_list = android_logger_list_alloc(mode, tail, pid); if (!logger_list) { return NULL; } if (!android_logger_open(logger_list, id)) { android_logger_list_free(logger_list); return NULL; } return logger_list;}/* prevent memory starvation when backfilling */static unsigned int queue_threshold(struct logger_list *logger_list){ return (logger_list->tail < 64) ? 64 : logger_list->tail;}static bool low_queue(struct listnode *node){ /* low is considered less than 2 */ return list_head(node) == list_tail(node);}static int android_logger_list_read_pstore(struct logger_list *logger_list, struct log_msg *log_msg){ ssize_t ret; off_t current, next; uid_t uid; struct logger *logger; struct __attribute__((__packed__)) { android_pmsg_log_header_t p; android_log_header_t l; } buf; static uint8_t preread_count; struct logger_list_logd* logger_list_logd = (struct logger_list_logd*)logger_list; memset(log_msg, 0, sizeof(*log_msg)); if (logger_list_logd->sock < 0) { int fd = open("/sys/fs/pstore/pmsg-ramoops-0", O_RDONLY); if (fd < 0) { return -errno; } logger_list_logd->sock = fd; preread_count = 0; } ret = 0; while(1) { if (preread_count < sizeof(buf)) { ret = TEMP_FAILURE_RETRY(read(logger_list_logd->sock, &buf.p.magic + preread_count, sizeof(buf) - preread_count)); if (ret < 0) { return -errno; } preread_count += ret; } if (preread_count != sizeof(buf)) { return preread_count ? -EIO : -EAGAIN; } if ((buf.p.magic != LOGGER_MAGIC) || (buf.p.len <= sizeof(buf)) || (buf.p.len > (sizeof(buf) + LOGGER_ENTRY_MAX_PAYLOAD)) || (buf.l.id >= LOG_ID_MAX) || (buf.l.realtime.tv_nsec >= NS_PER_SEC)) { do { memmove(&buf.p.magic, &buf.p.magic + 1, --preread_count); } while (preread_count && (buf.p.magic != LOGGER_MAGIC)); continue; } preread_count = 0; logger_for_each(logger, logger_list) { if (buf.l.id != logger->id) { continue; } if ((logger_list_logd->start.tv_sec || logger_list_logd->start.tv_nsec) && ((logger_list_logd->start.tv_sec > buf.l.realtime.tv_sec) || ((logger_list_logd->start.tv_sec == buf.l.realtime.tv_sec) && (logger_list_logd->start.tv_nsec > buf.l.realtime.tv_nsec)))) { break; } if (logger_list_logd->base.pid && (logger_list_logd->base.pid != buf.p.pid)) { break; } uid = get_best_effective_uid(); if (!uid_has_log_permission(uid) && (uid != buf.p.uid)) { break; } ret = TEMP_FAILURE_RETRY(read(logger_list_logd->sock, log_msg->entry_v3.msg, buf.p.len - sizeof(buf))); if (ret < 0) { return -errno; } if (ret != (ssize_t)(buf.p.len - sizeof(buf))) { return -EIO; } log_msg->entry_v3.len = buf.p.len - sizeof(buf); log_msg->entry_v3.hdr_size = sizeof(log_msg->entry_v3); log_msg->entry_v3.pid = buf.p.pid; log_msg->entry_v3.tid = buf.l.tid; log_msg->entry_v3.sec = buf.l.realtime.tv_sec; log_msg->entry_v3.nsec = buf.l.realtime.tv_nsec; log_msg->entry_v3.lid = buf.l.id; return ret; } current = TEMP_FAILURE_RETRY(lseek(logger_list_logd->sock, (off_t)0, SEEK_CUR)); if (current < 0) { return -errno; } next = TEMP_FAILURE_RETRY(lseek(logger_list_logd->sock, (off_t)(buf.p.len - sizeof(buf)), SEEK_CUR)); if (next < 0) { return -errno; } if ((next - current) != (ssize_t)(buf.p.len - sizeof(buf))) { return -EIO; } }}/* Flush queues in sequential order, one at a time */static int android_logger_list_flush(struct logger_list *logger_list, struct log_msg *log_msg){ int ret = 0; struct log_list *firstentry = NULL; struct logger_list_kernel* logger_list_kernel = (struct logger_list_kernel*)logger_list; while ((ret == 0) && (logger_list_kernel->flush || (logger_list_kernel->queued_lines > logger_list_kernel->base.tail))) { struct logger *logger; struct logger_kernel *logger_kernel; /* Merge sort */ bool at_least_one_is_low = false; struct logger *firstlogger = NULL; firstentry = NULL; logger_for_each(logger, logger_list) { struct listnode *node; struct log_list *oldest = NULL; /* kernel logger channels not necessarily time-sort order */ logger_kernel = (struct logger_kernel *)logger; list_for_each(node, &logger_kernel->log_list) { struct log_list *entry = node_to_item(node, struct log_list, node); if (!oldest || (entry->entry.entry.sec < oldest->entry.entry.sec) || ((entry->entry.entry.sec == oldest->entry.entry.sec) && (entry->entry.entry.nsec < oldest->entry.entry.nsec))) { oldest = entry; } } if (!oldest) { at_least_one_is_low = true; continue; } else if (low_queue(&logger_kernel->log_list)) { at_least_one_is_low = true; } if (!firstentry || (oldest->entry.entry.sec < firstentry->entry.entry.sec) || ((oldest->entry.entry.sec == firstentry->entry.entry.sec) && (oldest->entry.entry.nsec < firstentry->entry.entry.nsec))) { firstentry = oldest; firstlogger = logger; } } if (!firstentry) { break; } /* when trimming list, tries to keep one entry behind in each bucket */ if (!logger_list_kernel->flush && at_least_one_is_low && (logger_list_kernel->queued_lines < queue_threshold(logger_list))) { break; } /* within tail?, send! */ if ((logger_list_kernel->base.tail == 0) || (logger_list_kernel->queued_lines <= logger_list_kernel->base.tail)) { int diff; ret = firstentry->entry.entry.hdr_size; if (!ret) { ret = sizeof(firstentry->entry.entry_v1); } /* Promote entry to v3 format */ memcpy(log_msg->buf, firstentry->entry.buf, ret); diff = sizeof(firstentry->entry.entry_v3) - ret; if (diff < 0) { diff = 0; } else if (diff > 0) { memset(log_msg->buf + ret, 0, diff); } memcpy(log_msg->buf + ret + diff, firstentry->entry.buf + ret, firstentry->entry.entry.len + 1); ret += diff; log_msg->entry.hdr_size = ret; log_msg->entry.lid = firstlogger->id; ret += firstentry->entry.entry.len; } /* next entry */ list_remove(&firstentry->node); free(firstentry); if (logger_list_kernel->queued_lines) { logger_list_kernel->queued_lines--; } } /* Flushed the list, no longer in tail mode for continuing content */ if (logger_list_kernel->flush && !firstentry) { logger_list_kernel->base.tail = 0; } return ret;}static void caught_signal(int signum __unused){}/* Read from the selected logs */static int android_logger_list_read_logd(struct logger_list *logger_list, struct log_msg *log_msg){ int ret, e; struct logger *logger; struct sigaction ignore; struct sigaction old_sigaction; struct logger_list_logd *logger_list_logd = (struct logger_list_logd *)logger_list; unsigned int old_alarm = 0; if (!logger_list) { return -EINVAL; } if (logger_list->mode & ANDROID_LOG_PSTORE) { return android_logger_list_read_pstore(logger_list, log_msg); } if (logger_list->mode & ANDROID_LOG_NONBLOCK) { memset(&ignore, 0, sizeof(ignore)); ignore.sa_handler = caught_signal; sigemptyset(&ignore.sa_mask); } if (logger_list_logd->sock < 0) { char buffer[256], *cp, c; int sock = socket_local_client("logdr", ANDROID_SOCKET_NAMESPACE_RESERVED, SOCK_SEQPACKET); if (sock < 0) { if ((sock == -1) && errno) { return -errno; } return sock; } strcpy(buffer, (logger_list->mode & ANDROID_LOG_NONBLOCK) ? "dumpAndClose" : "stream"); cp = buffer + strlen(buffer); strcpy(cp, " lids"); cp += 5; c = '='; int remaining = sizeof(buffer) - (cp - buffer); logger_for_each(logger, logger_list) { ret = snprintf(cp, remaining, "%c%u", c, logger->id); ret = min(ret, remaining); remaining -= ret; cp += ret; c = ','; } if (logger_list->tail) { ret = snprintf(cp, remaining, " tail=%u", logger_list->tail); ret = min(ret, remaining); remaining -= ret; cp += ret; } if (logger_list_logd->start.tv_sec || logger_list_logd->start.tv_nsec) { ret = snprintf(cp, remaining, " start=%" PRIu32 ".%09" PRIu32, logger_list_logd->start.tv_sec, logger_list_logd->start.tv_nsec); ret = min(ret, remaining); remaining -= ret; cp += ret; } if (logger_list->pid) { ret = snprintf(cp, remaining, " pid=%u", logger_list->pid); ret = min(ret, remaining); remaining -= ret; cp += ret; } if (logger_list->mode & ANDROID_LOG_NONBLOCK) { /* Deal with an unresponsive logd */ sigaction(SIGALRM, &ignore, &old_sigaction); old_alarm = alarm(30); } ret = write(sock, buffer, cp - buffer); e = errno; if (logger_list->mode & ANDROID_LOG_NONBLOCK) { if (e == EINTR) { e = ETIMEDOUT; } alarm(old_alarm); sigaction(SIGALRM, &old_sigaction, NULL); } if (ret <= 0) { close(sock); if ((ret == -1) && e) { return -e; } if (ret == 0) { return -EIO; } return ret; } logger_list_logd->sock = sock; } ret = 0; while(1) { memset(log_msg, 0, sizeof(*log_msg)); if (logger_list->mode & ANDROID_LOG_NONBLOCK) { /* particularily useful if tombstone is reporting for logd */ sigaction(SIGALRM, &ignore, &old_sigaction); old_alarm = alarm(30); } /* NOTE: SOCK_SEQPACKET guarantees we read exactly one full entry */ ret = recv(logger_list_logd->sock, log_msg, LOGGER_ENTRY_MAX_LEN, 0); e = errno; if (logger_list->mode & ANDROID_LOG_NONBLOCK) { if ((ret == 0) || (e == EINTR)) { e = EAGAIN; ret = -1; } alarm(old_alarm); sigaction(SIGALRM, &old_sigaction, NULL); } if (ret <= 0) { if ((ret == -1) && e) { return -e; } return ret; } logger_for_each(logger, logger_list) { if (log_msg->entry.lid == logger->id) { return ret; } } } /* NOTREACH */ return ret;}/* Read from the selected logs */static int android_logger_list_read_kernel(struct logger_list *logger_list, struct log_msg *log_msg){ struct logger *logger; struct logger_list_kernel *logger_list_kernel = (struct logger_list_kernel *)logger_list; nfds_t nfds; struct pollfd *p, *pollfds = NULL; int error = 0, ret = 0; memset(log_msg, 0, sizeof(struct log_msg)); if (!logger_list) { return -ENODEV; } if (!(accessmode(logger_list->mode) & R_OK)) { logger_list_kernel->error = EPERM; goto done; } nfds = 0; logger_for_each(logger, logger_list) { ++nfds; } if (nfds <= 0) { error = ENODEV; goto done; } /* Do we have anything to offer from the buffer or state? */ if (logger_list_kernel->valid_entry) { /* implies we are also in a flush state */ goto flush; } ret = android_logger_list_flush(logger_list, log_msg); if (ret) { goto done; } if (logger_list_kernel->error) { /* implies we are also in a flush state */ goto done; } /* Lets start grinding on metal */ pollfds = calloc(nfds, sizeof(struct pollfd)); if (!pollfds) { error = ENOMEM; goto flush; } p = pollfds; struct logger_kernel *logger_kernel; logger_for_each(logger, logger_list) { logger_kernel = (struct logger_kernel *)logger; p->fd = logger_kernel->fd; p->events = POLLIN; logger_kernel->revents = &p->revents; ++p; } while (!ret && !error) { int result; /* If we oversleep it's ok, i.e. ignore EINTR. */ result = TEMP_FAILURE_RETRY( poll(pollfds, nfds, logger_list_kernel->timeout_ms)); if (result <= 0) { if (result) { error = errno; } else if (logger_list->mode & ANDROID_LOG_NONBLOCK) { error = EAGAIN; } else { logger_list_kernel->timeout_ms = LOG_TIMEOUT_NEVER; } logger_list_kernel->flush = true; goto try_flush; } logger_list_kernel->timeout_ms = LOG_TIMEOUT_FLUSH; /* Anti starvation */ if (!logger_list_kernel->flush && (logger_list_kernel->queued_lines > (queue_threshold(logger_list) / 2))) { /* Any queues with input pending that is low? */ bool starving = false; logger_for_each(logger, logger_list) { logger_kernel = (struct logger_kernel *)logger; if ((*(logger_kernel->revents) & POLLIN) && low_queue(&logger_kernel->log_list)) { starving = true; break; } } /* pushback on any queues that are not low */ if (starving) { logger_for_each(logger, logger_list) { logger_kernel = (struct logger_kernel *)logger; if ((*(logger_kernel->revents) & POLLIN) && !low_queue(&logger_kernel->log_list)) { *(logger_kernel->revents) &= ~POLLIN; } } } } logger_for_each(logger, logger_list) { unsigned int hdr_size; struct log_list *entry; int diff; logger_kernel = (struct logger_kernel *)logger; if (!(*(logger_kernel->revents) & POLLIN)) { continue; } memset(logger_list_kernel->entry.buf, 0, sizeof(struct log_msg)); /* NOTE: driver guarantees we read exactly one full entry */ result = read(logger_kernel->fd, logger_list_kernel->entry.buf, LOGGER_ENTRY_MAX_LEN); if (result <= 0) { if (!result) { error = EIO; } else if (errno != EINTR) { error = errno; } continue; } if (logger_list->pid && (logger_list->pid != logger_list_kernel->entry.entry.pid)) { continue; } hdr_size = logger_list_kernel->entry.entry.hdr_size; if (!hdr_size) { hdr_size = sizeof(logger_list_kernel->entry.entry_v1); } if ((hdr_size > sizeof(struct log_msg)) || (logger_list_kernel->entry.entry.len > sizeof(logger_list_kernel->entry.buf) - hdr_size) || (logger_list_kernel->entry.entry.len != result - hdr_size)) { error = EINVAL; continue; } /* Promote entry to v3 format */ diff = sizeof(logger_list_kernel->entry.entry_v3) - hdr_size; if (diff > 0) { if (logger_list_kernel->entry.entry.len > sizeof(logger_list_kernel->entry.buf) - hdr_size - diff) { error = EINVAL; continue; } result += diff; memmove(logger_list_kernel->entry.buf + hdr_size + diff, logger_list_kernel->entry.buf + hdr_size, logger_list_kernel->entry.entry.len + 1); memset(logger_list_kernel->entry.buf + hdr_size, 0, diff); logger_list_kernel->entry.entry.hdr_size = hdr_size + diff; } logger_list_kernel->entry.entry.lid = logger->id; /* speedup: If not tail, and only one list, send directly */ if (!logger_list->tail && (list_head(&logger_list->node) == list_tail(&logger_list->node))) { ret = result; memcpy(log_msg->buf, logger_list_kernel->entry.buf, result + 1); break; } entry = malloc(sizeof(*entry) - sizeof(entry->entry) + result + 1); if (!entry) { logger_list_kernel->valid_entry = true; error = ENOMEM; break; } logger_list_kernel->queued_lines++; memcpy(entry->entry.buf, logger_list_kernel->entry.buf, result); entry->entry.buf[result] = '\0'; list_add_tail(&logger_kernel->log_list, &entry->node); } if (ret <= 0) {try_flush: ret = android_logger_list_flush(logger_list, log_msg); } } free(pollfds);flush: if (error) { logger_list_kernel->flush = true; } if (ret <= 0) { ret = android_logger_list_flush(logger_list, log_msg); if (!ret && logger_list_kernel->valid_entry) { ret = logger_list_kernel->entry.entry.hdr_size; if (!ret) { ret = sizeof(logger_list_kernel->entry.entry_v1); } ret += logger_list_kernel->entry.entry.len; memcpy(log_msg->buf, logger_list_kernel->entry.buf, sizeof(struct log_msg)); logger_list_kernel->valid_entry = false; } }done: if (logger_list_kernel->error) { error = logger_list_kernel->error; } if (error) { logger_list_kernel->error = error; if (!ret) { ret = -error; } } return ret;}int android_logger_list_read(struct logger_list *logger_list, struct log_msg *log_msg){ if (use_logd) { return android_logger_list_read_logd(logger_list, log_msg); } else { return android_logger_list_read_kernel(logger_list, log_msg); }}/* Close all the logs */static void android_logger_list_free_logd(struct logger_list *logger_list){ if (logger_list == NULL) { return; } while (!list_empty(&logger_list->node)) { struct listnode *node = list_head(&logger_list->node); struct logger *logger = node_to_item(node, struct logger, node); android_logger_free(logger); } struct logger_list_logd *logger_list_logd = (struct logger_list_logd *)logger_list; if (use_logd) { if (logger_list_logd->sock >= 0) { close (logger_list_logd->sock); } } free(logger_list_logd);}/* Close all the logs */static void android_logger_list_free_kernel(struct logger_list *logger_list){ if (logger_list == NULL) { return; } while (!list_empty(&logger_list->node)) { struct listnode *node = list_head(&logger_list->node); struct logger *logger = node_to_item(node, struct logger, node); android_logger_free(logger); } struct logger_list_kernel *logger_list_kernel = (struct logger_list_kernel *)logger_list; free(logger_list_kernel);}void android_logger_list_free(struct logger_list *logger_list) { if (use_logd) { android_logger_list_free_logd(logger_list); } else { android_logger_list_free_kernel(logger_list); }}在logger.h中定义对外函数,FAKE_LOG_DEVICE==0 代表是手机版本，不是host。必须加这个宏，因为在编译host的使用也会引用到这个头文件，而在编译HOST的静态库时，log_read_common.c是不会参与编译的这样会造成set_uselogd这样函数没有定义。所以必须加这个宏。
......#if (FAKE_LOG_DEVICE == 0)void set_uselogd(int8_t uselogd);#endif......
最后我们来看logcat的main函数中，调用这个函数来控制logcat read log时使用logd机制还是kernel机制。下面这段代码是在logcat的main函数在定义完变量之后，和write相同也是看system/etc/disable_logd这个文件是否存在，存在就是kernel机制，不存在就是logd机制。
...... int fd; int8_t use_logd = 1; fd = open("system/etc/disable_logd", O_RDONLY); if (fd > 0) { LOGCAT_INFO("logcat disable logd.\n "); use_logd = 0; close(fd); } set_uselogd(use_logd);......write是在liblog库中log函数初始化的时候来判断使用哪个机制，也就是每个进程调用这个函数时都会初始化下。而read只有在logcat进程中使用，每次logcat进程启动的时候判断使用哪个机制，并且调用set_uselogd来通知read那块。
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