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决定彻底放弃对MooseFS的研究

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Release： 2016-06-07 15:06:13
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虽然对 分布式 也有一些了解，但是一直没有深入到代码去 研究 具体的实现。在群里咨询了一下，自己也google了一些资料，最终 决定 从MooseFS入手来深入 研究 分布式 系统 。第一步，就是从网上找文档，自己动手安装部署一番。官方网站上有一个中文的安装手册

  虽然对分布式也有一些了解，但是一直没有深入到代码去研究具体的实现。在群里咨询了一下，自己也google了一些资料，最终决定从MooseFS入手来深入研究分布式系统。第一步，就是从网上找文档，自己动手安装部署一番。官方网站上有一个中文的安装手册，非常nice，整个安装配置过程也非常顺利，感觉还不错，就是看它的代码实现。看完之后有些失望，在main函数中的第一个函数strerr_init（）中看到了这样的代码：

for (n=0 ; errtab[n].str ; n++) {}
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而errtab的定义（部分）如下所示： 

static errent errtab[] = {
#ifdef E2BIG
	{E2BIG,"E2BIG (Argument list too long)"},
#endif
#ifdef EACCES
	{EACCES,"EACCES (Permission denied)"},
#endif
......
	{0,NULL}
};
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很明显，那个循环仅仅是为了计算errtab中元素的个数，而这样的计算有必要用一个循环么？sizeof不能解决么？我实现看不出来作者这里要写一个循环的好处是什么？

  另一个地方让我感觉作者在写代码的时候很不用心，cfg_reload()在解析配置文件时定义了一个缓冲区linebuff[1000]数组来存储每行读取的内容。mfs解析配置文件时是按行读取的，每行的配置内容类似“key=value"这样的形式。这个缓冲区的长度定义为1000，也让我很不解。因为在定义缓冲区或分配内存的时候，一般都会考虑到对齐，都会对齐到word size或者CPU cache line的长度。这里的1000让我很不解！

  代码中还有很多无用的、多余的判断。例如下面的代码段：

    logappname = cfg_getstr("SYSLOG_IDENT",STR(APPNAME));

	if (rundaemon) {
		if (logappname[0]) {
			openlog(logappname, LOG_PID | LOG_NDELAY , LOG_DAEMON);
		} else {
			openlog(STR(APPNAME), LOG_PID | LOG_NDELAY , LOG_DAEMON);
		}
	}
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这个APPNAME是在编译的时候通过-DAPPNAME=mfsmaster这样的方式定义的一个宏，所以这个宏是必须定义的，否则前面的代码就没法运行（获取配置文件名称）。而且获取SYSLOG_IDENT配置变量的值是会指定默认值，所以if (logappname[0])这样的判断完全多余。如果是在两个函数中，这样的判断还说的过去，可是获取配置变量值的操作和
判断仅一个空行之隔，没必要到极点了吧。

  抛开这些细节性的东西不提，mfs选择的I/O复用机制也让人不敢恭维。现在需要监听套接字的读写事件，毫无疑问首选的eventpoll。如果没有记错的话，moosefs是07年开始的，这个时候内核中的eventpoll机制已经很完善了，实在不懂作者为什么要选用poll()来作为I/O复用的接口。在继续之前，先看一下下面的代码：

        i = poll(pdesc,ndesc,50);
		......
		if (i  我不明白在poll()返回-1时，为什么要检查EAGAIN错误。查看了man手册，只有EFAULT、EINTR、EINVAL、ENOMEM错误，看了一下内核代码，也没有返回EAGAIN错误的地方。而且很不明白，为什么在EAGAIN的时候要调用usleep()等待100毫秒，不理解！
<p>  最终<strong>彻底</strong>击穿我的信心的是matoclserv_gotpacket()函数，这个函数通过判断eptr->registered的值来做不同的三种处理，这三个代码块中很多都是可以合并的。要么给每种处理封装成一个函数，要么将这三块代码合并成一块，这样看着不是更简洁么？很多switch-case分支中的处理也不用区分eptr->registered的值，为什么写的这么庞大？难道作者在写的时候为了方便，复制粘贴了一番？反正我是很不理解，这样的代码风格真是让我没办法看下去，我<strong>决定</strong><strong>放弃</strong>了。我知道半途而废很不好，本来自己写代码风格就不好，怕看完之后更偏了，所以果断<strong>放弃</strong>！</p>
<p>  下面是matoclserv_gotpacket()函数的代码，大家欣赏一下：</p>
<p></p><pre name="code" class="cpp">void matoclserv_gotpacket(matoclserventry *eptr,uint32_t type,const uint8_t *data,uint32_t length) {
	if (type==ANTOAN_NOP) {
		return;
	}
	if (eptr->registered==0) {	// unregistered clients - beware that in this context sesdata is NULL
		switch (type) {
			case CLTOMA_FUSE_REGISTER:
				matoclserv_fuse_register(eptr,data,length);
				break;
			case CLTOMA_CSERV_LIST:
				matoclserv_cserv_list(eptr,data,length);
				break;
			case CLTOMA_SESSION_LIST:
				matoclserv_session_list(eptr,data,length);
				break;
			case CLTOAN_CHART:
				matoclserv_chart(eptr,data,length);
				break;
			case CLTOAN_CHART_DATA:
				matoclserv_chart_data(eptr,data,length);
				break;
			case CLTOMA_INFO:
				matoclserv_info(eptr,data,length);
				break;
			case CLTOMA_FSTEST_INFO:
				matoclserv_fstest_info(eptr,data,length);
				break;
			case CLTOMA_CHUNKSTEST_INFO:
				matoclserv_chunkstest_info(eptr,data,length);
				break;
			case CLTOMA_CHUNKS_MATRIX:
				matoclserv_chunks_matrix(eptr,data,length);
				break;
			case CLTOMA_QUOTA_INFO:
				matoclserv_quota_info(eptr,data,length);
				break;
			case CLTOMA_EXPORTS_INFO:
				matoclserv_exports_info(eptr,data,length);
				break;
			case CLTOMA_MLOG_LIST:
				matoclserv_mlog_list(eptr,data,length);
				break;
			default:
				syslog(LOG_NOTICE,"main master server module: got unknown message from unregistered (type:%"PRIu32")",type);
				eptr->mode=KILL;
		}
	} else if (eptr->registeredsesdata==NULL) {
			syslog(LOG_ERR,"registered connection without sesdata !!!");
			eptr->mode=KILL;
			return;
		}
		switch (type) {
			case CLTOMA_FUSE_REGISTER:
				matoclserv_fuse_register(eptr,data,length);
				break;
			case CLTOMA_FUSE_RESERVED_INODES:
				matoclserv_fuse_reserved_inodes(eptr,data,length);
				break;
			case CLTOMA_FUSE_STATFS:
				matoclserv_fuse_statfs(eptr,data,length);
				break;
			case CLTOMA_FUSE_ACCESS:
				matoclserv_fuse_access(eptr,data,length);
				break;
			case CLTOMA_FUSE_LOOKUP:
				matoclserv_fuse_lookup(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETATTR:
				matoclserv_fuse_getattr(eptr,data,length);
				break;
			case CLTOMA_FUSE_SETATTR:
				matoclserv_fuse_setattr(eptr,data,length);
				break;
			case CLTOMA_FUSE_READLINK:
				matoclserv_fuse_readlink(eptr,data,length);
				break;
			case CLTOMA_FUSE_SYMLINK:
				matoclserv_fuse_symlink(eptr,data,length);
				break;
			case CLTOMA_FUSE_MKNOD:
				matoclserv_fuse_mknod(eptr,data,length);
				break;
			case CLTOMA_FUSE_MKDIR:
				matoclserv_fuse_mkdir(eptr,data,length);
				break;
			case CLTOMA_FUSE_UNLINK:
				matoclserv_fuse_unlink(eptr,data,length);
				break;
			case CLTOMA_FUSE_RMDIR:
				matoclserv_fuse_rmdir(eptr,data,length);
				break;
			case CLTOMA_FUSE_RENAME:
				matoclserv_fuse_rename(eptr,data,length);
				break;
			case CLTOMA_FUSE_LINK:
				matoclserv_fuse_link(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETDIR:
				matoclserv_fuse_getdir(eptr,data,length);
				break;
/* CACHENOTIFY
			case CLTOMA_FUSE_DIR_REMOVED:
				matoclserv_fuse_dir_removed(eptr,data,length);
				break;
*/
			case CLTOMA_FUSE_OPEN:
				matoclserv_fuse_open(eptr,data,length);
				break;
			case CLTOMA_FUSE_READ_CHUNK:
				matoclserv_fuse_read_chunk(eptr,data,length);
				break;
			case CLTOMA_FUSE_WRITE_CHUNK:
				matoclserv_fuse_write_chunk(eptr,data,length);
				break;
			case CLTOMA_FUSE_WRITE_CHUNK_END:
				matoclserv_fuse_write_chunk_end(eptr,data,length);
				break;
// fuse - meta
			case CLTOMA_FUSE_GETTRASH:
				matoclserv_fuse_gettrash(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETDETACHEDATTR:
				matoclserv_fuse_getdetachedattr(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETTRASHPATH:
				matoclserv_fuse_gettrashpath(eptr,data,length);
				break;
			case CLTOMA_FUSE_SETTRASHPATH:
				matoclserv_fuse_settrashpath(eptr,data,length);
				break;
			case CLTOMA_FUSE_UNDEL:
				matoclserv_fuse_undel(eptr,data,length);
				break;
			case CLTOMA_FUSE_PURGE:
				matoclserv_fuse_purge(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETRESERVED:
				matoclserv_fuse_getreserved(eptr,data,length);
				break;
			case CLTOMA_FUSE_CHECK:
				matoclserv_fuse_check(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETTRASHTIME:
				matoclserv_fuse_gettrashtime(eptr,data,length);
				break;
			case CLTOMA_FUSE_SETTRASHTIME:
				matoclserv_fuse_settrashtime(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETGOAL:
				matoclserv_fuse_getgoal(eptr,data,length);
				break;
			case CLTOMA_FUSE_SETGOAL:
				matoclserv_fuse_setgoal(eptr,data,length);
				break;
			case CLTOMA_FUSE_APPEND:
				matoclserv_fuse_append(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETDIRSTATS:
				matoclserv_fuse_getdirstats_old(eptr,data,length);
				break;
			case CLTOMA_FUSE_TRUNCATE:
				matoclserv_fuse_truncate(eptr,data,length);
				break;
			case CLTOMA_FUSE_REPAIR:
				matoclserv_fuse_repair(eptr,data,length);
				break;
			case CLTOMA_FUSE_SNAPSHOT:
				matoclserv_fuse_snapshot(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETEATTR:
				matoclserv_fuse_geteattr(eptr,data,length);
				break;
			case CLTOMA_FUSE_SETEATTR:
				matoclserv_fuse_seteattr(eptr,data,length);
				break;
/* do not use in version before 1.7.x */
			case CLTOMA_FUSE_QUOTACONTROL:
				matoclserv_fuse_quotacontrol(eptr,data,length);
				break;
/* for tools - also should be available for registered clients */
			case CLTOMA_CSERV_LIST:
				matoclserv_cserv_list(eptr,data,length);
				break;
			case CLTOMA_SESSION_LIST:
				matoclserv_session_list(eptr,data,length);
				break;
			case CLTOAN_CHART:
				matoclserv_chart(eptr,data,length);
				break;
			case CLTOAN_CHART_DATA:
				matoclserv_chart_data(eptr,data,length);
				break;
			case CLTOMA_INFO:
				matoclserv_info(eptr,data,length);
				break;
			case CLTOMA_FSTEST_INFO:
				matoclserv_fstest_info(eptr,data,length);
				break;
			case CLTOMA_CHUNKSTEST_INFO:
				matoclserv_chunkstest_info(eptr,data,length);
				break;
			case CLTOMA_CHUNKS_MATRIX:
				matoclserv_chunks_matrix(eptr,data,length);
				break;
			case CLTOMA_QUOTA_INFO:
				matoclserv_quota_info(eptr,data,length);
				break;
			case CLTOMA_EXPORTS_INFO:
				matoclserv_exports_info(eptr,data,length);
				break;
			case CLTOMA_MLOG_LIST:
				matoclserv_mlog_list(eptr,data,length);
				break;
			default:
				syslog(LOG_NOTICE,"main master server module: got unknown message from mfsmount (type:%"PRIu32")",type);
				eptr->mode=KILL;
		}
	} else {	// old mfstools
		if (eptr->sesdata==NULL) {
			syslog(LOG_ERR,"registered connection (tools) without sesdata !!!");
			eptr->mode=KILL;
			return;
		}
		switch (type) {
// extra (external tools)
			case CLTOMA_FUSE_REGISTER:
				matoclserv_fuse_register(eptr,data,length);
				break;
			case CLTOMA_FUSE_READ_CHUNK:	// used in mfsfileinfo
				matoclserv_fuse_read_chunk(eptr,data,length);
				break;
			case CLTOMA_FUSE_CHECK:
				matoclserv_fuse_check(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETTRASHTIME:
				matoclserv_fuse_gettrashtime(eptr,data,length);
				break;
			case CLTOMA_FUSE_SETTRASHTIME:
				matoclserv_fuse_settrashtime(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETGOAL:
				matoclserv_fuse_getgoal(eptr,data,length);
				break;
			case CLTOMA_FUSE_SETGOAL:
				matoclserv_fuse_setgoal(eptr,data,length);
				break;
			case CLTOMA_FUSE_APPEND:
				matoclserv_fuse_append(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETDIRSTATS:
				matoclserv_fuse_getdirstats(eptr,data,length);
				break;
			case CLTOMA_FUSE_TRUNCATE:
				matoclserv_fuse_truncate(eptr,data,length);
				break;
			case CLTOMA_FUSE_REPAIR:
				matoclserv_fuse_repair(eptr,data,length);
				break;
			case CLTOMA_FUSE_SNAPSHOT:
				matoclserv_fuse_snapshot(eptr,data,length);
				break;
			case CLTOMA_FUSE_GETEATTR:
				matoclserv_fuse_geteattr(eptr,data,length);
				break;
			case CLTOMA_FUSE_SETEATTR:
				matoclserv_fuse_seteattr(eptr,data,length);
				break;
/* do not use in version before 1.7.x */
			case CLTOMA_FUSE_QUOTACONTROL:
				matoclserv_fuse_quotacontrol(eptr,data,length);
				break;
/* ------ */
			default:
				syslog(LOG_NOTICE,"main master server module: got unknown message from mfstools (type:%"PRIu32")",type);
				eptr->mode=KILL;
		}
	}
}
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