44               Head                           Tail
50               Tail                                 Head
126     UINT32 tail = g_dmesgInfo->logTail;  in OsDmesgRead()  local
139     if (head < tail) { /* Case A */  in OsDmesgRead()
376     UINT32 tail = g_dmesgInfo->logTail;  in OsBufFullWrite()  local
384         ret = memcpy_s(buf + tail, bufSize - tail, dst, bufSize - tail);  in OsBufFullWrite()
389         ret = memcpy_s(buf, bufSize, dst + bufSize - tail, tail);  in OsBufFullWrite()
397         if (logLen > (bufSize - tail)) { /* need cycle back to start */  in OsBufFullWrite()
398             ret = memcpy_s(buf + tail, bufSize - tail, dst, bufSize - tail);  in OsBufFullWrite()
403             ret = memcpy_s(buf, bufSize, dst + bufSize - tail, logLen - (bufSize - tail));  in OsBufFullWrite()
409             g_dmesgInfo->logTail = logLen - (bufSize - tail);  in OsBufFullWrite()
412             ret = memcpy_s(buf + tail, bufSize - tail, dst, logLen);  in OsBufFullWrite()
431     UINT32 tail = g_dmesgInfo->logTail;  in OsWriteTailToHead()  local
440         ret = memcpy_s(buf + tail, bufSize - tail, dst, writeLen);  in OsWriteTailToHead()
450         ret = memcpy_s(buf + tail, bufSize - tail, dst, logLen);  in OsWriteTailToHead()
465     UINT32 tail = g_dmesgInfo->logTail;  in OsWriteTailToEnd()  local
472     if (logLen >= (bufSize - tail)) { /* need cycle to start ,then became B */  in OsWriteTailToEnd()
473         writeLen = bufSize - tail;  in OsWriteTailToEnd()
474         ret = memcpy_s(buf + tail, writeLen, dst, writeLen);  in OsWriteTailToEnd()
482         if (g_dmesgInfo->logSize == g_logBufSize) { /* Tail = Head is 0 */  in OsWriteTailToEnd()
488         ret = memcpy_s(buf + tail, bufSize - tail, dst, logLen);  in OsWriteTailToEnd()
674     UINT32 logSize, bufSize, head, tail, intSave;  in LOS_DmesgToFile()  local
685     tail = g_dmesgInfo->logTail;  in LOS_DmesgToFile()
699     if (head < tail) {  in LOS_DmesgToFile()
709         ret = memcpy_s(buf + bufSize - head, logSize - (bufSize - head), logBuf, tail);  in LOS_DmesgToFile()