LVM2里各类元数据操做集

1. label相关操做

lib/format_text/text_label.c：

struct label_ops _text_ops = { 
        .can_handle = _text_can_handle,
        .write = _text_write,
        .read = _text_read,
        .verify = _text_can_handle,
        .initialise_label = _text_initialise_label,
        .destroy_label = _text_destroy_label,
        .destroy = _fmt_text_destroy,
};

2. mda (metadata area)相关操做

format-text.c/format-text.c:

lvm2的元数据是以纯文本方式表达的，可读性很好。元数据能够放在磁盘开始的1M空间里，也能够放在/etc/lvm/backup/目录下的文件里。

文件元数据处理：

static struct metadata_area_ops _metadata_text_file_ops = {
        .vg_read = _vg_read_file,
        .vg_read_precommit = _vg_read_precommit_file,
        .vg_write = _vg_write_file,
        .vg_remove = _vg_remove_file,
        .vg_commit = _vg_commit_file
};

磁盘元数据处理：

static struct metadata_area_ops _metadata_text_raw_ops = {
        .vg_read = _vg_read_raw,
        .vg_read_precommit = _vg_read_precommit_raw,
        .vg_write = _vg_write_raw,
        .vg_remove = _vg_remove_raw,
        .vg_precommit = _vg_precommit_raw,
        .vg_commit = _vg_commit_raw,
        .vg_revert = _vg_revert_raw,
        .mda_metadata_locn_copy = _metadata_locn_copy_raw,
        .mda_metadata_locn_name = _metadata_locn_name_raw,
        .mda_metadata_locn_offset = _metadata_locn_offset_raw,
        .mda_free_sectors = _mda_free_sectors_raw,
        .mda_total_sectors = _mda_total_sectors_raw,
        .mda_in_vg = _mda_in_vg_raw,
        .pv_analyze_mda = _pv_analyze_mda_raw,
        .mda_locns_match = _mda_locns_match_raw,
        .mda_get_device = _mda_get_device_raw,
        .mda_export_text = _mda_export_text_raw,
        .mda_import_text = _mda_import_text_raw
};

备份文件中元数据处理，备份文件和普通文件有什么区别呢？

static struct metadata_area_ops _metadata_text_file_backup_ops = {
        .vg_read = _vg_read_file,
        .vg_write = _vg_write_file,
        .vg_remove = _vg_remove_file,
        .vg_commit = _vg_commit_file_backup
};

3. 抽象格式处理集

如上述，元数据处理有不一样的操做集，相似VFS和具体文件系统的关系，得有一个抽象的处理集。

static struct format_handler _text_handler = {
        .scan = _text_scan,
        .pv_read = _text_pv_read,
        .pv_initialise = _text_pv_initialise,
        .pv_setup = _text_pv_setup,
        .pv_add_metadata_area = _text_pv_add_metadata_area,
        .pv_remove_metadata_area = _text_pv_remove_metadata_area,
        .pv_resize = _text_pv_resize,
        .pv_write = _text_pv_write,
        .pv_needs_rewrite = _text_pv_needs_rewrite,
        .vg_setup = _text_vg_setup,
        .lv_setup = _text_lv_setup,
        .create_instance = _text_create_text_instance,
        .destroy_instance = _text_destroy_instance,
        .destroy = _text_destroy
};

struct format_type *create_text_format(struct cmd_context *cmd) 就像一个工厂函数，根据命令，实例化匹配的元数据处理集。

struct labeller *text_labeller_create(const struct format_type *fmt) 负责实例化标签处理， 而后在标签和文本处理结构间作cross-link.