glusterfs中xlator的介绍(1)

转自:glusterfs中xlator的介绍
在Gluster中，所有的操作都围绕着一条主线，那就是xlator，在对应的volume的配置中可以看到

volume testvol-client-0
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_0
    option remote-host 192.168.1.194
end-volume

volume testvol-client-1
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_1
    option remote-host 192.168.1.194
end-volume

volume testvol-client-2
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_2
    option remote-host 192.168.1.194
end-volume

volume testvol-client-3
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_3
    option remote-host 192.168.1.194
end-volume

volume testvol-client-4
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_4
    option remote-host 192.168.1.194
end-volume

volume testvol-client-5
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_5
    option remote-host 192.168.1.194
end-volume

volume testvol-client-6
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_6
    option remote-host 192.168.1.194
end-volume

volume testvol-client-7
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_7
    option remote-host 192.168.1.194
end-volume

volume testvol-client-8
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_8
    option remote-host 192.168.1.194
end-volume

volume testvol-client-9
    type protocol/client
    option transport-type tcp
    option remote-subvolume /opt/data/data_9
    option remote-host 192.168.1.194
end-volume

volume testvol-stripe-0
    type cluster/stripe
    subvolumes testvol-client-0 testvol-client-1
end-volume

volume testvol-stripe-1
    type cluster/stripe
    subvolumes testvol-client-2 testvol-client-3
end-volume

volume testvol-stripe-2
    type cluster/stripe
    subvolumes testvol-client-4 testvol-client-5
end-volume

volume testvol-stripe-3
    type cluster/stripe
    subvolumes testvol-client-6 testvol-client-7
end-volume

volume testvol-stripe-4
    type cluster/stripe
    subvolumes testvol-client-8 testvol-client-9
end-volume

volume testvol-dht
    type cluster/distribute
    subvolumes testvol-stripe-0 testvol-stripe-1 testvol-stripe-2 testvol-stripe-3 testvol-stripe-4
end-volume

volume testvol-write-behind
    type performance/write-behind
    subvolumes testvol-dht
end-volume

volume testvol-read-ahead
    type performance/read-ahead
    subvolumes testvol-write-behind
end-volume

volume testvol-io-cache
    type performance/io-cache
    subvolumes testvol-read-ahead
end-volume

volume testvol-quick-read
    type performance/quick-read
    subvolumes testvol-io-cache
end-volume

volume testvol-open-behind
    type performance/open-behind
    subvolumes testvol-quick-read
end-volume

volume testvol-md-cache
    type performance/md-cache
    subvolumes testvol-open-behind
end-volume

volume testvol
    type debug/io-stats
    option count-fop-hits off
    option latency-measurement off
    subvolumes testvol-md-cache
end-volume

根据配置文件看到，volume名为testvol， 类型为debug/io-stats，操作count-fop-hits与latency-measurement对应的value为off，然后通过subvolumes来进入下一个xlator，其中，subvolumes后面的value即为下一层xlator。
从gluster的代码目录结构中，可以看到debug/io-stat这个目录

[root@CM glusterfs]# ls
aclocal.m4       autom4te.cache  config.h.in    configure.ac    cscope.files   doc                  glusterfs-hadoop   libglusterfs  Makefile.in  rfc.sh        tests
api              ChangeLog       config.log     contrib         cscope.in.out  extras               glusterfs.spec     libtool       missing      rpc           THANKS
argp-standalone  cli             config.status  CONTRIBUTING    cscope.out     glusterfs-api.pc     glusterfs.spec.in  ltmain.sh     NEWS         run-tests.sh  xlators
AUTHORS          config.guess    config.sub     COPYING-GPLV2   cscope.po.out  glusterfs-api.pc.in  INSTALL            Makefile      py-compile   stamp-h1
autogen.sh       config.h        configure      COPYING-LGPLV3  depcomp        glusterfsd           install-sh         Makefile.am   README       tags
[root@CM glusterfs]# ls xlators/
bindings  cluster  debug  encryption  features  lib  Makefile  Makefile.am  Makefile.in  meta  mgmt  mount  nfs  performance  playground  protocol  storage  system
[root@CM glusterfs]# ls xlators/debug/
error-gen  io-stats  Makefile  Makefile.am  Makefile.in  trace
[root@CM glusterfs]# ls xlators/debug/io-stats/
Makefile  Makefile.am  Makefile.in  src
[root@CM glusterfs]# 

可以看到，io-stats存在debug目录中，debug目录存在xlators中。
看一下xlators/debug/io-stats/src/下io-stats的实现

struct xlator_fops fops = {
        .stat        = io_stats_stat,
        .readlink    = io_stats_readlink,
        .mknod       = io_stats_mknod,
        .mkdir       = io_stats_mkdir,
        .unlink      = io_stats_unlink,
        .rmdir       = io_stats_rmdir,
        .symlink     = io_stats_symlink,
        .rename      = io_stats_rename,
        .link        = io_stats_link,
        .truncate    = io_stats_truncate,
        .open        = io_stats_open,
        .readv       = io_stats_readv,
        .writev      = io_stats_writev,
        .statfs      = io_stats_statfs,
        .flush       = io_stats_flush,
        .fsync       = io_stats_fsync,
        .setxattr    = io_stats_setxattr,
        .getxattr    = io_stats_getxattr,
        .removexattr = io_stats_removexattr,
        .fsetxattr    = io_stats_fsetxattr,
        .fgetxattr    = io_stats_fgetxattr,
        .fremovexattr = io_stats_fremovexattr,
        .opendir     = io_stats_opendir,
        .readdir     = io_stats_readdir,
        .readdirp    = io_stats_readdirp,
        .fsyncdir    = io_stats_fsyncdir,
        .access      = io_stats_access,
        .ftruncate   = io_stats_ftruncate,
        .fstat       = io_stats_fstat,
        .create      = io_stats_create,
        .lk          = io_stats_lk,
        .inodelk     = io_stats_inodelk,
        .finodelk    = io_stats_finodelk,
        .entrylk     = io_stats_entrylk,
        .lookup      = io_stats_lookup,
        .xattrop     = io_stats_xattrop,
        .fxattrop    = io_stats_fxattrop,
        .setattr     = io_stats_setattr,
        .fsetattr    = io_stats_fsetattr,
    .fallocate   = io_stats_fallocate,
    .discard     = io_stats_discard,
};

fops为glusterfs中对文件操作的一个亮点，fops中包含定义如下：

struct xlator_fops {
        fop_lookup_t         lookup;
        fop_stat_t           stat;
        fop_fstat_t          fstat;
        fop_truncate_t       truncate;
        fop_ftruncate_t      ftruncate;
        fop_access_t         access;
        fop_readlink_t       readlink;
        fop_mknod_t          mknod;
        fop_mkdir_t          mkdir;
        fop_unlink_t         unlink;
        fop_rmdir_t          rmdir;
        fop_symlink_t        symlink;
        fop_rename_t         rename;
        fop_link_t           link;
        fop_create_t         create;
        fop_open_t           open;
        fop_readv_t          readv;
        fop_writev_t         writev;
        fop_flush_t          flush;
        fop_fsync_t          fsync;
        fop_opendir_t        opendir;
        fop_readdir_t        readdir;
        fop_readdirp_t       readdirp;
        fop_fsyncdir_t       fsyncdir;
        fop_statfs_t         statfs;
        fop_setxattr_t       setxattr;
        fop_getxattr_t       getxattr;
        fop_fsetxattr_t      fsetxattr;
        fop_fgetxattr_t      fgetxattr;
        fop_removexattr_t    removexattr;
        fop_fremovexattr_t   fremovexattr;
        fop_lk_t             lk;
        fop_inodelk_t        inodelk;
        fop_finodelk_t       finodelk;
        fop_entrylk_t        entrylk;
        fop_fentrylk_t       fentrylk;
        fop_rchecksum_t      rchecksum;
        fop_xattrop_t        xattrop;
        fop_fxattrop_t       fxattrop;
        fop_setattr_t        setattr;
        fop_fsetattr_t       fsetattr;
        fop_getspec_t        getspec;
	fop_fallocate_t	     fallocate;
	fop_discard_t	     discard;

        /* these entries are used for a typechecking hack in STACK_WIND _only_ */
        fop_lookup_cbk_t         lookup_cbk;
        fop_stat_cbk_t           stat_cbk;
        fop_fstat_cbk_t          fstat_cbk;
        fop_truncate_cbk_t       truncate_cbk;
        fop_ftruncate_cbk_t      ftruncate_cbk;
        fop_access_cbk_t         access_cbk;
        fop_readlink_cbk_t       readlink_cbk;
        fop_mknod_cbk_t          mknod_cbk;
        fop_mkdir_cbk_t          mkdir_cbk;
        fop_unlink_cbk_t         unlink_cbk;
        fop_rmdir_cbk_t          rmdir_cbk;
        fop_symlink_cbk_t        symlink_cbk;
        fop_rename_cbk_t         rename_cbk;
        fop_link_cbk_t           link_cbk;
        fop_create_cbk_t         create_cbk;
        fop_open_cbk_t           open_cbk;
        fop_readv_cbk_t          readv_cbk;
        fop_writev_cbk_t         writev_cbk;
        fop_flush_cbk_t          flush_cbk;
        fop_fsync_cbk_t          fsync_cbk;
        fop_opendir_cbk_t        opendir_cbk;
        fop_readdir_cbk_t        readdir_cbk;
        fop_readdirp_cbk_t       readdirp_cbk;
        fop_fsyncdir_cbk_t       fsyncdir_cbk;
        fop_statfs_cbk_t         statfs_cbk;
        fop_setxattr_cbk_t       setxattr_cbk;
        fop_getxattr_cbk_t       getxattr_cbk;
        fop_fsetxattr_cbk_t      fsetxattr_cbk;
        fop_fgetxattr_cbk_t      fgetxattr_cbk;
        fop_removexattr_cbk_t    removexattr_cbk;
        fop_fremovexattr_cbk_t   fremovexattr_cbk;
        fop_lk_cbk_t             lk_cbk;
        fop_inodelk_cbk_t        inodelk_cbk;
        fop_finodelk_cbk_t       finodelk_cbk;
        fop_entrylk_cbk_t        entrylk_cbk;
        fop_fentrylk_cbk_t       fentrylk_cbk;
        fop_rchecksum_cbk_t      rchecksum_cbk;
        fop_xattrop_cbk_t        xattrop_cbk;
        fop_fxattrop_cbk_t       fxattrop_cbk;
        fop_setattr_cbk_t        setattr_cbk;
        fop_fsetattr_cbk_t       fsetattr_cbk;
        fop_getspec_cbk_t        getspec_cbk;
	fop_fallocate_cbk_t	 fallocate_cbk;
	fop_discard_cbk_t	 discard_cbk;
};

fops中定义了88个接口，fops定义在xlator.h中，其中定义的每个接口都很重要，都为文件操作对应的接口，例如open,read,write,opendir,readdir,stat等。不过不用担心，88个接口挨个实现一下其实也需要精力，但是在某些场景下，其中的有些接口不会被用到，这是可以不必定义该接口，当本xlator中并未定义对应的接口时，xlator核心部分默认将会使用default.c中的对应的接口，例如前面的例子，stat与stat_cbk的例子，io-stats中并未定义stat_cbk，而在fops结构中却有stat_cbk的接口，这个时候如果用户使用stat_cbk时，将会调用default.c中的stat_cbk,default中的stat_cbk定义在libglusterfs/src/defaults.c。那么怎么使用的default这个接口的呢，可以参考xlator.c中的对应的使用:libglusterfs/src/xlator.c

int
xlator_dynload (xlator_t *xl)
{
        int                ret = -1; 
        char              *name = NULL;
        void              *handle = NULL;
        volume_opt_list_t *vol_opt = NULL;
        class_methods_t   *vtbl = NULL;

        GF_VALIDATE_OR_GOTO ("xlator", xl, out);

        INIT_LIST_HEAD (&xl->volume_options);

        ret = gf_asprintf (&name, "%s/%s.so", XLATORDIR, xl->type);
        if (-1 == ret) {
                gf_log ("xlator", GF_LOG_ERROR, "asprintf failed");
                goto out;
        }   

        ret = -1; 

        gf_log ("xlator", GF_LOG_TRACE, "attempt to load file %s", name);

        handle = dlopen (name, RTLD_NOW|RTLD_GLOBAL);
        if (!handle) {
                gf_log ("xlator", GF_LOG_WARNING, "%s", dlerror ());
                goto out;
        }   
        xl->dlhandle = handle;

        if (!(xl->fops = dlsym (handle, "fops"))) {
                gf_log ("xlator", GF_LOG_WARNING, "dlsym(fops) on %s",
                        dlerror ());
                goto out;
        }   

        if (!(xl->cbks = dlsym (handle, "cbks"))) {
                gf_log ("xlator", GF_LOG_WARNING, "dlsym(cbks) on %s",
                        dlerror ());
                goto out;
        }   

        /*  
         * If class_methods exists, its contents override any definitions of
          * init or fini for that translator.  Otherwise, we fall back to the
         * older method of looking for init and fini directly.
         */
        vtbl = dlsym(handle,"class_methods");
        if (vtbl) {
                xl->init        = vtbl->init;
                xl->fini        = vtbl->fini;
                xl->reconfigure = vtbl->reconfigure;
                xl->notify      = vtbl->notify;
        }
        else {
                if (!(*VOID(&xl->init) = dlsym (handle, "init"))) {
                        gf_log ("xlator", GF_LOG_WARNING, "dlsym(init) on %s",
                                dlerror ());
                        goto out;
                }

                if (!(*VOID(&(xl->fini)) = dlsym (handle, "fini"))) {
                        gf_log ("xlator", GF_LOG_WARNING, "dlsym(fini) on %s",
                                dlerror ());
                        goto out;
                }
                if (!(*VOID(&(xl->reconfigure)) = dlsym (handle,
                                                         "reconfigure"))) {
                        gf_log ("xlator", GF_LOG_TRACE,
                                "dlsym(reconfigure) on %s -- neglecting",
                                dlerror());
                }
                if (!(*VOID(&(xl->notify)) = dlsym (handle, "notify"))) {
                        gf_log ("xlator", GF_LOG_TRACE,
                                "dlsym(notify) on %s -- neglecting",
                                dlerror ());
                }

        }

        if (!(xl->dumpops = dlsym (handle, "dumpops"))) {
                gf_log ("xlator", GF_LOG_TRACE,
                        "dlsym(dumpops) on %s -- neglecting", dlerror ());
        }

        if (!(*VOID(&(xl->mem_acct_init)) = dlsym (handle, "mem_acct_init"))) {

                gf_log (xl->name, GF_LOG_TRACE,
                        "dlsym(mem_acct_init) on %s -- neglecting",
                        dlerror ());
        }

        vol_opt = GF_CALLOC (1, sizeof (volume_opt_list_t),
                         gf_common_mt_volume_opt_list_t);

        if (!vol_opt) {
                goto out;
        }

        if (!(vol_opt->given_opt = dlsym (handle, "options"))) {
                dlerror ();
                gf_log (xl->name, GF_LOG_TRACE,
                        "Strict option validation not enforced -- neglecting");
        }
        INIT_LIST_HEAD (&vol_opt->list);
        list_add_tail (&vol_opt->list, &xl->volume_options);

        fill_defaults (xl);

        ret = 0;

out:
        GF_FREE (name);
        return ret;
}

再次回到刚才所查看的配置中的type部分，当配置文件解析解析了volname以后，看到type为debug/io-stats，debug/io-stats为一个xlator，在xlator中将会打开这个debug/io-stats，打开的操作就是在xlator_dynload接口中进行，XLATORDIR为glusterfs对应的动态库所存储的根目录，XLATORDIR的定义是在Makefile时所传递。

[root@CM glusterfs]# ls /usr/local/lib/glusterfs/
3git
[root@CM glusterfs]# ls /usr/local/lib/glusterfs/3git/
auth  rpc-transport  xlator
[root@CM glusterfs]# ls /usr/local/lib/glusterfs/3git/xlator/
cluster  debug  encryption  features  mgmt  mount  nfs  performance  protocol  storage  system  testing
[root@CM glusterfs]# ls /usr/local/lib/glusterfs/3git/xlator/debug/
error-gen.la  error-gen.so  io-stats.la  io-stats.so  trace.la  trace.so
[root@CM glusterfs]# 

例如我在编译的时候，将路径指定在/usr/local/lib/glusterfs/3git/xlator/中，这时xlator_dynload中将会打开该目录下的debug/io-stats.so。

 if (!(xl->fops = dlsym (handle, "fops"))) {
                gf_log ("xlator", GF_LOG_WARNING, "dlsym(fops) on %s",
                        dlerror ());
                goto out;
        }   

然后通过dlsym，将fops导出至xl->fops中
在后面通过 fill_defaults (xl);将xlator中并未定义的fops接口补充进xl中

#define SET_DEFAULT_FOP(fn) do {			\
                if (!xl->fops->fn)			\
                        xl->fops->fn = default_##fn;	\
        } while (0)

#define SET_DEFAULT_CBK(fn) do {			\
                if (!xl->cbks->fn)			\
                        xl->cbks->fn = default_##fn;	\
        } while (0)


static void
fill_defaults (xlator_t *xl)
{
        if (xl == NULL)	{
                gf_log_callingfn ("xlator", GF_LOG_WARNING, "invalid argument");
                return;
        }

        SET_DEFAULT_FOP (create);
        SET_DEFAULT_FOP (open);
        SET_DEFAULT_FOP (stat);
        SET_DEFAULT_FOP (readlink);
        SET_DEFAULT_FOP (mknod);
        SET_DEFAULT_FOP (mkdir);
        SET_DEFAULT_FOP (unlink);
        SET_DEFAULT_FOP (rmdir);
        SET_DEFAULT_FOP (symlink);
        SET_DEFAULT_FOP (rename);
        SET_DEFAULT_FOP (link);
        SET_DEFAULT_FOP (truncate);
        SET_DEFAULT_FOP (readv);
        SET_DEFAULT_FOP (writev);
        SET_DEFAULT_FOP (statfs);
        SET_DEFAULT_FOP (flush);
        SET_DEFAULT_FOP (fsync);
        SET_DEFAULT_FOP (setxattr);
        SET_DEFAULT_FOP (getxattr);
        SET_DEFAULT_FOP (fsetxattr);
        SET_DEFAULT_FOP (fgetxattr);
        SET_DEFAULT_FOP (removexattr);
        SET_DEFAULT_FOP (fremovexattr);
        SET_DEFAULT_FOP (opendir);
        SET_DEFAULT_FOP (readdir);
        SET_DEFAULT_FOP (readdirp);
        SET_DEFAULT_FOP (fsyncdir);
        SET_DEFAULT_FOP (access);
        SET_DEFAULT_FOP (ftruncate);
        SET_DEFAULT_FOP (fstat);
        SET_DEFAULT_FOP (lk);
        SET_DEFAULT_FOP (inodelk);
        SET_DEFAULT_FOP (finodelk);
        SET_DEFAULT_FOP (entrylk);
        SET_DEFAULT_FOP (fentrylk);
        SET_DEFAULT_FOP (lookup);
        SET_DEFAULT_FOP (rchecksum);
        SET_DEFAULT_FOP (xattrop);
        SET_DEFAULT_FOP (fxattrop);
        SET_DEFAULT_FOP (setattr);
        SET_DEFAULT_FOP (fsetattr);
	SET_DEFAULT_FOP (fallocate);
	SET_DEFAULT_FOP (discard);

        SET_DEFAULT_FOP (getspec);

        SET_DEFAULT_CBK (release);
        SET_DEFAULT_CBK (releasedir);
        SET_DEFAULT_CBK (forget);

        if (!xl->notify)
                xl->notify = default_notify;

        if (!xl->mem_acct_init)
                xl->mem_acct_init = default_mem_acct_init;

        return;
}

通过SET_DEFAULT_FOP以及SET_DEFAULT_CBK来补充尚未定义的fops接口，其实现通过宏来进行，首先判断对应的接口是否已经实现，尚未实现就将default填充入对应的接口。

关于接口的定义以及使用工作流程已经大概的讲完了，接下来查看io-stats对应的option部分的定义

struct volume_options options[] = {
        { .key  = {"dump-fd-stats"},
          .type = GF_OPTION_TYPE_BOOL,
          .default_value = "off",
          .description = "If on stats related to file-operations would be "
                         "tracked inside GlusterFS data-structures."
        },
        { .key  = { "latency-measurement" },
          .type = GF_OPTION_TYPE_BOOL,
          .default_value = "off",
          .description = "If on stats related to the latency of each operation "
                         "would be tracked inside GlusterFS data-structures. "
        },
        { .key  = {"count-fop-hits"},
          .type = GF_OPTION_TYPE_BOOL,
        },
        { .key = {"log-level"},
          .type = GF_OPTION_TYPE_STR,
          .value = { "DEBUG", "WARNING", "ERROR", "INFO",
                     "CRITICAL", "NONE", "TRACE"}
        },

        /* These are synthetic entries to assist validation of CLI's  *
         *  volume set  command                                       */
        { .key = {"client-log-level"},
          .type = GF_OPTION_TYPE_STR,
          .default_value = "INFO",
          .description = "Changes the log-level of the clients",
          .value = { "DEBUG", "WARNING", "ERROR", "INFO",
                     "CRITICAL", "NONE", "TRACE"}
        },
        { .key = {"sys-log-level"},
          .type = GF_OPTION_TYPE_STR,
          .default_value = "CRITICAL",
          .description = "Gluster's syslog log-level",
          .value = { "WARNING", "ERROR", "INFO", "CRITICAL"}
        },
        { .key = {"brick-log-level"},
          .type = GF_OPTION_TYPE_STR,
          .default_value = "INFO",
          .description = "Changes the log-level of the bricks",
          .value = { "DEBUG", "WARNING", "ERROR", "INFO",
                     "CRITICAL", "NONE", "TRACE"}
        },
        { .key  = {NULL} },

};

在配置文件中，可以看到io-stats中的option中包含了两个配置：

 option count-fop-hits off
 option latency-measurement off

这两个位置都是通过前面的option定义的：
volume_options定义如下：

/*每一个translator 应该定义一下这个结构体*/
typedef struct volume_options {
        char                    *key[ZR_VOLUME_MAX_NUM_KEY];
        /* 不同的key, 一样的含义 */
        volume_option_type_t    type;
        double                  min;  /* 0 means no range */
        double                  max;  /* 0 means no range */
        char                    *value[ZR_OPTION_MAX_ARRAY_SIZE];
        /* If specified, will check for one of
           the value from this array */
        char                    *default_value;
        char                    *description; /* about the key */
        /* Required for int options where only the min value
         * is given and is 0. This will cause validation not to
         * happen
         */
        opt_validate_type_t     validate;
} volume_option_t;

其中type为volume_option_type_t,该类型定义为:

typedef enum {
        GF_OPTION_TYPE_ANY = 0,
        GF_OPTION_TYPE_STR,
        GF_OPTION_TYPE_INT,
        GF_OPTION_TYPE_SIZET,
        GF_OPTION_TYPE_PERCENT,
        GF_OPTION_TYPE_PERCENT_OR_SIZET,
        GF_OPTION_TYPE_BOOL,
        GF_OPTION_TYPE_XLATOR,
        GF_OPTION_TYPE_PATH,
        GF_OPTION_TYPE_TIME,
        GF_OPTION_TYPE_DOUBLE,
        GF_OPTION_TYPE_INTERNET_ADDRESS,
        GF_OPTION_TYPE_INTERNET_ADDRESS_LIST,
        GF_OPTION_TYPE_PRIORITY_LIST,
        GF_OPTION_TYPE_SIZE_LIST,
        GF_OPTION_TYPE_MAX,
} volume_option_type_t;

在io-stats中看到的两个option，在io-stats中将会被使用，两个选项都为BOOL型，由于其传递字符串为off，将会被转化为BOOL型进行使用。
通过执行xlator中的xl->init，来执行的io-stats中的init接口，init接口同样是在xlater_dyload中加载到xl中的。而option，需要在init中进行设置，设置操作如下：

        ret = ios_init_top_stats (conf);
        if (ret)
                return -1;

        GF_OPTION_INIT ("dump-fd-stats", conf->dump_fd_stats, bool, out);
        GF_OPTION_INIT ("count-fop-hits", conf->count_fop_hits, bool, out);
        GF_OPTION_INIT ("latency-measurement", conf->measure_latency, bool, out);

关于option配置中的off字符串转化为BOOL，将通过接口dict_get_str_boolean来得到bool值：
dict_get_str_boolean实现如下：

/**
 * dict_get_str_boolean - get a boolean value based on string representation.
 *
 * @this        : dictionary
 * @key         : dictionary key queried
 * @default_val : default value if key not found
 *
 * @return      : @default_val if key not found
 *              : boolean interpretation of @this[@key] if it makes sense
 *                (ie., "on", "true", "enable" ...)
 *              : -1 if error occurs or @this[@key] doesn't make sens as
 *                  boolean
 *
 *   So if you query a boolean option, then via @default_val you can choose
 *   between following patterns:
 *
 *   - fall back to _gf_false if @key is not set  [@default_val = 0]
 *   - fall back to _gf_true if @key is not set   [@default_val = 1]
 *   - regard as failure if @key is not set       [@default_val = -1]
 *   - handle specially (not as error) if @key is not set
 *                                                [@default_val = anything else]
 */

int
dict_get_str_boolean (dict_t *this, char *key, int default_val)
{       
        data_t       *data = NULL;
        gf_boolean_t  boo = _gf_false; 
        int           ret  = 0;
        
        ret = dict_get_with_ref (this, key, &data);
        if (ret < 0) {
                if (ret == -ENOENT)
                        ret = default_val;
                else  
                        ret = -1;
                goto err;
        }
        
        GF_ASSERT (data);
        
        if (!data->data) {
                ret = -1;

                goto err;
        }

        ret = gf_string2boolean (data->data, &boo);
        if (ret == -1)
                goto err;

        ret = boo;

err:
        if (data)
                data_unref (data);

        return ret;
}

通过gf_string2boolean将字符串幻化为bool：

int
gf_string2boolean (const char *str, gf_boolean_t *b)
{
        if (str == NULL) {
                gf_log_callingfn (THIS->name, GF_LOG_WARNING, "argument invalid");
                return -1;
        }

        if ((strcasecmp (str, "1") == 0) ||
            (strcasecmp (str, "on") == 0) ||
            (strcasecmp (str, "yes") == 0) ||
            (strcasecmp (str, "true") == 0) ||
            (strcasecmp (str, "enable") == 0)) {
                *b = _gf_true;
                return 0;
        }

        if ((strcasecmp (str, "0") == 0) ||
            (strcasecmp (str, "off") == 0) ||
            (strcasecmp (str, "no") == 0) ||
            (strcasecmp (str, "false") == 0) ||
            (strcasecmp (str, "disable") == 0)) {
                *b = _gf_false; 
                return 0;
        }

        return -1;
}

所以，option如果为bool型时，对应的配置可以为数字，on/off， yes/no，true/false，enable/disable。
关于option的设置以及读取，通过字典操作很方面dict_set/dict_get操作。
关于基础的介绍，大概就这么多