Re: [PATCH 1/4] lib/fonts: Look up glyph data with font_data_glyph_buf()

[Jocelyn Falempe <jfalempe@redhat.com>]

On 29/05/2026 16:01, Thomas Zimmermann wrote:
> Add font_data_glyph_buf() to retrieve a character's glyph data or NULL
> otherwise. Console fonts can currently contain 256 or 512 glyphs. The
> kernel-internal characters are of type char, unsigned short or unsigned
> int. Catch all of them by accepting unsigned int. Callers possibly have
> to cast from signed to unsigned types to reach all glyphs in a font.

Thanks, yes I missed to check font_data_num_glyphs(), and using signed 
index is also problematic.

Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>

> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>   include/linux/font.h |  3 +++
>   lib/fonts/fonts.c    | 31 +++++++++++++++++++++++++++++++
>   2 files changed, 34 insertions(+)
> 
> diff --git a/include/linux/font.h b/include/linux/font.h
> index 6845f02d739a..ea23b727388b 100644
> --- a/include/linux/font.h
> +++ b/include/linux/font.h
> @@ -101,6 +101,9 @@ font_data_t *font_data_import(const struct console_font *font, unsigned int vpit
>   void font_data_get(font_data_t *fd);
>   bool font_data_put(font_data_t *fd);
>   unsigned int font_data_size(font_data_t *fd);
> +const unsigned char *font_data_glyph_buf(font_data_t *fd,
> +					 unsigned int width, unsigned int vpitch,
> +					 unsigned int c);
>   bool font_data_is_equal(font_data_t *lhs, font_data_t *rhs);
>   int font_data_export(font_data_t *fd, struct console_font *font, unsigned int vpitch);
>   
> diff --git a/lib/fonts/fonts.c b/lib/fonts/fonts.c
> index f5d5333450a0..4fc66722d00d 100644
> --- a/lib/fonts/fonts.c
> +++ b/lib/fonts/fonts.c
> @@ -178,6 +178,37 @@ unsigned int font_data_size(font_data_t *fd)
>   }
>   EXPORT_SYMBOL_GPL(font_data_size);
>   
> +static unsigned int font_data_num_glyphs(font_data_t *fd, unsigned int width, unsigned int height)
> +{
> +	return font_data_size(fd) / font_glyph_size(width, height);
> +}
> +
> +/**
> + * font_data_glyph_buf() - Returns the glyph for a specific character as raw bytes
> + * @fd: The font data
> + * @width: The glyph width in bits per scanline
> + * @vpitch: The number of scanlines per glyph
> + * @c: The character
> + *
> + * Glyphs start at fixed intervals within the font data. font_data_glyph_buf()
> + * returns the glyph shape of the specified character. If no such glyph
> + * exists in the font, it returns NULL.
> + *
> + * Returns:
> + * The character's raw glyph shape, or NULL if no glyph exists for the character. The
> + * provided buffer is read-only.
> + */
> +const unsigned char *font_data_glyph_buf(font_data_t *fd,
> +					 unsigned int width, unsigned int vpitch,
> +					 unsigned int c)
> +{
> +	if (c >= font_data_num_glyphs(fd, width, vpitch))
> +		return NULL;
> +
> +	return font_data_buf(fd) + font_glyph_size(width, vpitch) * c;
> +}
> +EXPORT_SYMBOL_GPL(font_data_glyph_buf);
> +
>   /**
>    * font_data_is_equal - Compares font data for equality
>    * @lhs: Left-hand side font data