fix[DFS][littlefs]: align lseek callback signature with off_t

[wdfk-prog]

拉取/合并请求描述：(PR description)

[

为什么提交这份PR (why to submit this PR)

RT-Thread PR #11486 中反馈，最新版 littlefs 在 Keil 编译场景下会出现 DFS lseek 回调函数指针类型不兼容问题：DFS 文件操作表期望 off_t (*)(struct dfs_file *, off_t)，但 littlefs 适配层当前非 DFS_V2 分支的 _dfs_lfs_lseek 参数通过 DFS_LFS_LSEEK_PARAMS 展开为 rt_off_t offset。

虽然 rt_off_t 在 RT-Thread 中确实存在，并定义为 rt_base_t，但它不等价于 DFS lseek 接口签名要求中的 off_t。在部分工具链/配置下，rt_off_t 的底层类型可能是 signed int，而 off_t 的底层类型可能是 signed long，从而导致函数指针签名不兼容。

我这里使用 GCC + DFS_V1 没有出现 warning。分析原因是该构建使用了 newlib，并定义了 RT_USING_LIBC；通过工具查看最终链路可见该 GCC 工具链中 __INT32_TYPE__ 为 long int，因此 rt_off_t 最终也会落到 long，未触发类型不兼容问题。

littlefs 当前 CI 编译使用 bsp/qemu-vexpress-a9，该路径没有暴露问题；由于没有很好的方案在 CI 中模拟 Keil/IAR 的具体 typedef 实现，这一类兼容性仍需要实际 Keil/IAR 工程验证。

你的解决方案是什么 (what is your solution)

1. 将非 DFS_V2 分支中的 DFS_LFS_LSEEK_PARAMS 从 rt_off_t offset 改为 off_t offset，使 _dfs_lfs_lseek 的函数签名与 RT-Thread DFS lseek 回调原型保持一致。
2. 将 littlefs 文件位置回写处统一按 DFS 文件结构字段类型处理：文件当前位置使用 off_t，文件大小使用 size_t。
3. 加入参数接口签名检查，使 RT-Thread 5.0.2 及之后的 DFS_V1 配置在编译期确认 _dfs_lfs_lseek 与 DFS 期望的 lseek 签名一致：

#if !defined(RT_USING_DFS_V2) && defined(RT_VERSION_CHECK) && (RTTHREAD_VERSION >= RT_VERSION_CHECK(5, 0, 2))
typedef off_t (*dfs_lfs_lseek_expected_t)(struct dfs_file *file, off_t offset);
static dfs_lfs_lseek_expected_t dfs_lfs_lseek_type_check = _dfs_lfs_lseek;
#endif /* !defined(RT_USING_DFS_V2) && defined(RT_VERSION_CHECK) && (RTTHREAD_VERSION >= RT_VERSION_CHECK(5, 0, 2)) */

这里检查变量绑定到实际的静态函数 _dfs_lfs_lseek，避免仅修改函数实现但没有覆盖到 DFS 回调签名的问题。

请提供验证的bsp和config (provide the config and bsp)

• BSP:

bsp/qemu-vexpress-a9，用于 littlefs 现有 GCC CI 路径验证。Keil/IAR 兼容性问题来源于 RT-Thread PR #11486 中的实际工程反馈，仍建议在受影响的 Keil/IAR 工程中做最终验证。

• .config:

无需新增配置项。相关验证配置包括：

RT_USING_DFS_V1
PKG_USING_LITTLEFS

GCC 未复现 warning 的路径还包含 RT_USING_LIBC / newlib 的类型定义影响。

• action:

not provided yet. 现有 littlefs CI 使用 bsp/qemu-vexpress-a9，不能覆盖 Keil/IAR 的 typedef 差异；Keil/IAR 仍需实际工程验证。

]

当前拉取/合并请求的状态 Intent for your PR

必须选择一项 Choose one (Mandatory):

• 本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
• 本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

• 已经仔细查看过代码改动的对比 Already check the difference between PR and old code
• 代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
• 没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已经被注释了的代码 All redundant code is removed and cleaned up
• 所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
• 对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
• 代码是高质量的 Code in this PR is of high quality
• 已经使用formatting 等源码格式化工具确保格式符合RT-Thread代码规范 This PR complies with RT-Thread code specification
• 如果是新增bsp, 已经添加ci检查到.github/ALL_BSP_COMPILE.json 详细请参考链接BSP自查

Summary by CodeRabbit

Bug Fixes

• Improved file truncation and position handling in LittleFS operations for better compatibility across different RT-Thread versions and build configurations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 441c0fab-7bdc-43de-9eb8-905fce3f4bfa

📥 Commits

Reviewing files that changed from the base of the PR and between beab78f and c441163.

📒 Files selected for processing (1)

• dfs_lfs.c

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Walkthrough

The PR replaces rt_off_t with POSIX off_t in the DFS_LFS_LSEEK_PARAMS and DFS_LFS_STORE_FILE_POS seek ABI macros across all four conditional build branches in dfs_lfs.c, and similarly updates the post-truncation metadata casts in the RT_FIOFTRUNCATE ioctl path.

Changes

rt_off_t → off_t type correction in seek ABI and truncate ioctl

Layer / File(s)	Summary
Seek ABI macros across all build variants dfs_lfs.c	DFS_LFS_LSEEK_PARAMS offset type and DFS_LFS_STORE_FILE_POS cast changed from rt_off_t to off_t in all four conditional branches: RT 5.0.2+ non-DFS-v2 (line 88–91), DFS v1 split (line 117–120), RT 5.0.0 transition (line 145–148), and RT 4.x legacy (line 173–176).
RT_FIOFTRUNCATE ioctl metadata casts dfs_lfs.c	Post-truncate metadata in the DFS v2 RT_FIOFTRUNCATE path updated to assign DFS_LFS_FILE_POS via (off_t)pos and DFS_LFS_FILE_SIZE via (size_t)pos, replacing the prior rt_off_t-based position cast.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• RT-Thread-packages/littlefs#30: Modifies _dfs_lfs_lseek directory offset↔pos conversions in dfs_lfs.c, overlapping with the lseek ABI and file position bookkeeping changed here.
• RT-Thread-packages/littlefs#31: Also modifies the DFS v2 RT_FIOFTRUNCATE path's post-truncation file position/size metadata, including switching casts to off_t/size_t.

Suggested reviewers

• Rbb666

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: aligning lseek callback signature with off_t type in littlefs DFS module.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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