lfs_file_rawopencfg(lfs_t *lfs, lfs_file_t *file,
|       const char *path, int flags,
|       const struct lfs_file_config *cfg) 
|   // 1. 根據(jù)路徑查找對(duì)應(yīng)tag和id
|   // 此時(shí)查找的為REG類型的tag，查找到的文件id存儲(chǔ)在file->id
|-> lfs_stag_t tag = lfs_dir_find(lfs, &file->m, &path, &file->id);
|
|   // 2. 根據(jù)文件id查找文件數(shù)據(jù)對(duì)應(yīng)tag
|   // 此時(shí)查找的為STRUCT類型的tag，包括inline文件和outline文件
|-> tag = lfs_dir_get(lfs, &file->m, LFS_MKTAG(0x700, 0x3ff, 0),
|       LFS_MKTAG(LFS_TYPE_STRUCT, file->id, 8), &file->ctz);
|
|-> ...

// 該函數(shù)用于遍歷時(shí)查找匹配的tag，如打開文件時(shí)查找匹配文件的對(duì)應(yīng)tag
lfs_stag_t lfs_dir_fetchmatch(lfs_t *lfs,
|       lfs_mdir_t *dir, const lfs_block_t pair[2],
|       lfs_tag_t fmask, lfs_tag_t ftag, uint16_t *id,
|       int (*cb)(void *data, lfs_tag_t tag, const void *buffer), void *data) 
|-> ...
|
|   // 如果當(dāng)前遍歷到的tag的類型為DELETE，且其id與tempbesttag中id相同
|   // 則將tempbesttag置為無(wú)效。
|-> if (tag == (LFS_MKTAG(LFS_TYPE_DELETE, 0, 0) |
|            (LFS_MKTAG(0, 0x3ff, 0) & tempbesttag))) {
|       tempbesttag |= 0x80000000;
|   }
|-> ...

int lfs_dir_fetch(lfs_t *lfs,
    lfs_mdir_t *dir, // fetch tail結(jié)果存儲(chǔ)在dir->tail中
    const lfs_block_t pair[2] // 父目錄元數(shù)據(jù)對(duì)所在塊
) {
    // 調(diào)用lfs_dir_fetchmatch實(shí)現(xiàn)
    // 其中fmask、ftag為-1，表示不進(jìn)行匹配，會(huì)fetch到元數(shù)據(jù)末尾
    return (int)lfs_dir_fetchmatch(lfs, dir, pair,
            (lfs_tag_t)-1, (lfs_tag_t)-1, NULL, NULL, NULL);
}

lfs_mdir_t m = dir.m;
while (m.split) {
    lfs_dir_fetch(lfs, &m, m.tail);
}

static lfs_stag_t lfs_dir_fetchmatch(lfs_t *lfs,
|       lfs_mdir_t *dir, const lfs_block_t pair[2],
|       lfs_tag_t fmask, lfs_tag_t ftag, uint16_t *id,
|       int (*cb)(void *data, lfs_tag_t tag, const void *buffer), void *data) {
|   // 用besttag保存最佳匹配結(jié)果
|-> lfs_stag_t besttag = -1;
|
|-> ...
|
|   // 準(zhǔn)備用于暫存每次匹配中的最佳匹配結(jié)果、更新等變量
|-> uint16_t tempcount = 0;
|   lfs_block_t temptail[2] = {LFS_BLOCK_NULL, LFS_BLOCK_NULL};
|   bool tempsplit = false;
|   lfs_stag_t tempbesttag = besttag;
|
|   // fetch主流程
|-> while (true) {
    |   // 1. 從磁盤中解析下一個(gè)tag并計(jì)算tag的CRC
    |-> lfs_bd_read(lfs,
    |           NULL, &lfs->rcache, lfs->cfg->block_size,
    |           dir->pair[0], off, &tag, sizeof(tag));
    |   crc = lfs_crc(crc, &tag, sizeof(tag));
    |   tag = lfs_frombe32(tag) ^ ptag;
    |
    |   // 2. 檢查邊界，當(dāng)不在范圍內(nèi)或tag無(wú)效時(shí)跳出循環(huán)
    |-> if (!lfs_tag_isvalid(tag)) {
    |       dir->erased = (lfs_tag_type1(ptag) == LFS_TYPE_CRC &&
    |               dir->off % lfs->cfg->prog_size == 0);
    |       break;
    |   } else if (off + lfs_tag_dsize(tag) > lfs->cfg->block_size) {
    |       dir->erased = false;
    |       break;
    |   }
    |
    |   // 3. 如果tag為CRC，則檢查CRC并更新最佳匹配結(jié)果
    |-> if (lfs_tag_type1(tag) == LFS_TYPE_CRC) {
        |   // 3.1 檢查CRC
        |-> uint32_t dcrc;
        |   lfs_bd_read(lfs,
        |           NULL, &lfs->rcache, lfs->cfg->block_size,
        |           dir->pair[0], off+sizeof(tag), &dcrc, sizeof(dcrc));
        |   if (crc != dcrc) {
        |       dir->erased = false;
        |       break;
        |   }
        |
        |   // 3.2 更新最佳匹配結(jié)果等
        |-> besttag = tempbesttag;
        |   dir->off = off + lfs_tag_dsize(tag);
        |   dir->etag = ptag;
        |   dir->count = tempcount;
        |   dir->tail[0] = temptail[0];
        |   dir->tail[1] = temptail[1];
        |   dir->split = tempsplit;
        |
        |   // 3.3 重置CRC
        |-> crc = 0xffffffff;
        |   continue;
        }
    |
    |   // 4. 計(jì)算entry的CRC
    |-> for (lfs_off_t j = sizeof(tag); j < lfs_tag_dsize(tag); j++) {
    |       uint8_t dat;
    |       lfs_bd_read(lfs,
    |               NULL, &lfs->rcache, lfs->cfg->block_size,
    |               dir->pair[0], off+j, &dat, 1);
    |       ...
    |       crc = lfs_crc(crc, &dat, 1);
    |   }
    |
    |   // 5. 根據(jù)tag類型進(jìn)行相應(yīng)更新
    |-> if (lfs_tag_type1(tag) == LFS_TYPE_NAME) {
    |       // 5.1 tag為NAME類型，則根據(jù)其中id更新目錄中count 
    |       // 目錄中的最后一個(gè)id為count-1
    |       if (lfs_tag_id(tag) >= tempcount) {
    |           tempcount = lfs_tag_id(tag) + 1;
    |       }
    |   } else if (lfs_tag_type1(tag) == LFS_TYPE_SPLICE) {
    |       // 5.2 tag為DELETE類型，如果id和目前的最佳匹配結(jié)果對(duì)應(yīng)
    |       // 則將最佳匹配結(jié)果置為無(wú)效
    |       if (tag == (LFS_MKTAG(LFS_TYPE_DELETE, 0, 0) |
    |               (LFS_MKTAG(0, 0x3ff, 0) & tempbesttag))) {
    |           tempbesttag |= 0x80000000;
    |       }
    |       ...
    |   } else if (lfs_tag_type1(tag) == LFS_TYPE_TAIL) {
    |       // 5.3 tag為TAIL類型，則更新tempsplit和temptail
    |       tempsplit = (lfs_tag_chunk(tag) & 1);
    |       lfs_bd_read(lfs,
    |               NULL, &lfs->rcache, lfs->cfg->block_size,
    |               dir->pair[0], off+sizeof(tag), &temptail, 8);
    |       ...
    |   }
    |
    |   // 6. 先用fmask和ftag參數(shù)進(jìn)行初次匹配
    |-> if ((fmask & tag) == (fmask & ftag)) {
    |       // 6.1 如果匹配則調(diào)用cb回調(diào)函數(shù)進(jìn)行進(jìn)一步匹配 
    |       int res = cb(data, tag, &(struct lfs_diskoff){
    |               dir->pair[0], off+sizeof(tag)});
    |       ... 
    |       // 6.2 如果匹配成功則更新到最佳匹配結(jié)果 
    |       if (res == LFS_CMP_EQ) {
    |           tempbesttag = tag;
    |       } else if (...)
    |           ...
    |       }
    |   }
|
|   // 如果讀到結(jié)束，則根據(jù)最佳匹配結(jié)果返回相應(yīng)值
|-> if (dir->off > 0) {
|       ... 
|
|       if (lfs_tag_isvalid(besttag)) {
|           return besttag;
|       } else if (lfs_tag_id(besttag) < dir->count) {
|           return LFS_ERR_NOENT;
|       } else {
|           return 0;
|       }
|   }
|
|-> ...