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

[Thomas Zimmermann]

Hi

Am 01.06.26 um 13:18 schrieb Jocelyn Falempe:
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 <jfale...@redhat.com>

Thanks for reviewing. I'll merge the series in a few days if no other 
comments come in.

Best regards
Thomas



Signed-off-by: Thomas Zimmermann <tzimmerm...@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


--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)