fix(freetype): fix using memfs to create a FT font

[hpfaz]

Description of the feature or fix

lv_freetype_req_face_id drops path metadata when using memfs,
fix uses drive letter to adjust malloc/memcpy length when creating
the cache node.

To reproduce:

in lv_conf.h : #define LV_FREETYPE_USE_LVGL_PORT 1, #define LV_USE_FREETYPE 1, LV_USE_FS_MEMFS 1
snippet:

lv_fs_path_ex_t font_path = {0};
lv_fs_make_path_from_buffer(&font_path,
    LV_FS_MEMFS_LETTER,
    buffer_p,
    buffer_sz);
lv_font_t *font_p =
    lv_freetype_font_create(
        (char const*)&font_path,
        LV_FREETYPE_FONT_RENDER_MODE_BITMAP,
        font_sz,
        LV_FREETYPE_FONT_STYLE_NORMAL);

Result:

Program will most likely crash due to OOB memory accesses when trying to use path metadata.

Notes

• Update the Documentation if needed.
• Add Examples if relevant.
• Add Tests if applicable.
• If you added new options to lv_conf_template.h run lv_conf_internal_gen.py and update Kconfig.
• Run scripts/code-format.py (astyle needs to be installed) and follow the Code Conventions
• Mark the Pull request as Draft while you are working on the first version, and mark is as Ready when it's ready for review.
• When changes were requested, re-request review to notify the maintainers.
• Help us to review this Pull Request! Anyone can approve or request changes.

[C47D]

Looks good to me. Please run the code-format.py in the scripts directory and then commit the formated file.

[PGNetHun]

Please use lv_strdup, and you can remove lv_malloc and LV_ASSERT_MALLOC
https://github.com/lvgl/lvgl/blob/master/src/stdlib/builtin/lv_string_builtin.c#L209

See example usage: https://github.com/lvgl/lvgl/blob/master/src/draw/lv_image_decoder.c#L241

[hpfaz]

Hi @PGNetHun ,

Actually this can't be used here because when you use memfs the path is actually a pointer to a lv_fs_path_ex_t object. The first field of this structure is a null terminated string.
When cast to char * subsequent use of strlen will only copy the first field of the structure thus leading to the loss of the relevant metadata for proper use of memfs.
I hope that clears out why I used this hack on len and malloc.

[PGNetHun]

Yes, that makes sense.

[PGNetHun]

please fix C code formatting issue

[PGNetHun]

Yes, that makes sense.

[XuNeo]

LGTM