关于卷的配置文件(Volume Spec)

Glusterfs使用了xlator模块化架构，用户可以通过编辑卷的配置文件来自定义xlator的结构。下面本人结合源码，说说从配置文件构建xlator结构的流程。

 

首先要说明的是glusterfs根据执行程序名字的不同，有三种启动方式：glusterd,  server , client, 具体可见函数glusterfsd/src/glusterfsd.c:gf_get_process_mode

 

 

static uint8_t
gf_get_process_mode (char *exec_name)
{
        char *dup_execname = NULL, *base = NULL;
        uint8_t ret = 0;

        dup_execname = gf_strdup (exec_name);
        base = basename (dup_execname);

        if (!strncmp (base, "glusterfsd", 10)) {
                ret = GF_SERVER_PROCESS;
        } else if (!strncmp (base, "glusterd", 8)) {
                ret = GF_GLUSTERD_PROCESS;
        } else {
                ret = GF_CLIENT_PROCESS;
        }

        GF_FREE (dup_execname);

        return ret;
}

 

 

 

然后请跳到glusterfsd/src/glusterfsd.c: main 函数，它是glusterfs的入口函数。

 

 之后有glusterfs_volumes_init 这样一个函数, 我们将从这个函数分析起

 

int
glusterfs_volumes_init (glusterfs_ctx_t *ctx)
{
        FILE               *fp = NULL;
        cmd_args_t         *cmd_args = NULL;
        int                 ret = 0;

        cmd_args = &ctx->cmd_args;

        if (cmd_args->sock_file) {
                ret = glusterfs_listener_init (ctx);
                if (ret)     
                        goto out;                                                                                     
        }
        //如果在启动的时候指定volfile_server（意味着启动的是client），将会返回。
        if (cmd_args->volfile_server) { 
                ret = glusterfs_mgmt_init (ctx);
                /* return, do not emancipate() yet */                                                                 
                return ret;                                                                                           
        }
       //获得cmd_args->volfile文件的fp
        fp = get_volfp (ctx);        

        if (!fp) {
                gf_log ("glusterfsd", GF_LOG_ERROR,                                                                   
                        "Cannot reach volume specification file");                                                    
                ret = -1;                                                                                             
                goto out;

       }
        //解析volfile文件，构建xlator结构
        ret = glusterfs_process_volfp (ctx, fp);
        if (ret)
                goto out;

out:
        emancipate (ctx, ret);
        return ret;
}

 

 

    下面进入glusterfs_process_volfp函数：

 

 

int
glusterfs_process_volfp (glusterfs_ctx_t *ctx, FILE *fp)                                                              
{
        glusterfs_graph_t  *graph = NULL;
        int                 ret = -1;
        xlator_t           *trav = NULL;     
       
        //glusterfs使用flex和bison为volfile发明了一种简单的编程语言
        //这个函数定义在libglusterfs/src/y.tab.c 中
        graph = glusterfs_graph_construct (fp);      
        if (!graph) {                        
                gf_log ("", GF_LOG_ERROR, "failed to construct the graph");                                           
                goto out;    
        }
        //如果有fuse xlator在volfile中，则报错返回。
        for (trav = graph->first; trav; trav = trav->next) {                                                          
                if (strcmp (trav->type, "mount/fuse") == 0) {
                        gf_log ("glusterfsd", GF_LOG_ERROR,                                                           
                                "fuse xlator cannot be specified "                                                    
                                "in volume file");                                                                    
                        goto out;
                }
        }
        
        ret = glusterfs_graph_prepare (graph, ctx);                                                                   
        if (ret) {
                glusterfs_graph_destroy (graph);                                                                      
                goto out;    
        }

        ret = glusterfs_graph_activate (graph, ctx);

        if (ret) {
                glusterfs_graph_destroy (graph);
                goto out;
        }

        gf_log_volume_file (fp);

        ret = 0;
out:
        if (fp)
                fclose (fp);

        if (ret && !ctx->active) {
                /* there is some error in setting up the first graph itself */
                cleanup_and_exit (0);
        }

        return ret;
}