fpi-log: Add functions to dump bytes

Drivers may need to to hex-dumps for debugging purposes, so expose what
we already had in the fpi transfers in the internal API

doc/libfprint-2-sections.txt

@@ -348,6 +348,8 @@ fpi_image_device_set_bz3_threshold
 <SECTION>
 <FILE>fpi-log</FILE>
 fp_dbg
+fp_dbg_hex_dump_bytes
+fp_dbg_hex_dump_data
 fp_info
 fp_warn
 fp_err

libfprint/fpi-log.c

@@ -0,0 +1,74 @@
+/*
+ * FpiLog - Internal logging functions
+ * Copyright (C) 2020 Benjamin Berg <bberg@redhat.com>
+ * Copyright (C) 2025 Joshua Grisham <josh@joshuagrisham.com>
+ * Copyright (C) 2026 Marco Trevisan (Treviño) <mail@3v1n0.net>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "fpi-log.h"
+
+/**
+ * fpi_dbg_hex_dump_data:
+ * @buf: Bytes buffer to dump
+ * @len: Length of @buf to dump
+ *
+ * Prints hex dump of @buf to fp_dbg()
+ */
+void
+  (fpi_dbg_hex_dump_data) (const gchar  *log_domain,
+                           const guint8 *buf,
+                           gsize len)
+{
+  g_autoptr(GString) line = NULL;
+
+  if (g_log_writer_default_would_drop (G_LOG_LEVEL_DEBUG, log_domain))
+    return;
+
+  if (G_UNLIKELY (len == 0 || !buf))
+    return;
+
+  line = g_string_new ("");
+
+  for (gint i = 0; i < len; i++)
+    {
+      g_string_append_printf (line, "%02x ", buf[i]);
+      if ((i + 1) % 16 == 0)
+        {
+          g_log (log_domain, G_LOG_LEVEL_DEBUG, "%s", line->str);
+          g_string_set_size (line, 0);
+        }
+    }
+
+  if (line->len)
+    g_log (log_domain, G_LOG_LEVEL_DEBUG, "%s", line->str);
+}
+
+/**
+ * fpi_dbg_hex_dump_bytes:
+ * @bytes: #GBytes to dump
+ *
+ * Prints hex dump of @bytes to fp_dbg()
+ */
+void
+  (fpi_dbg_hex_dump_bytes) (const gchar *log_domain,
+                            GBytes      *bytes)
+{
+  gsize length = 0;
+  const guint8 *data = g_bytes_get_data (bytes, &length);
+
+  (fpi_dbg_hex_dump_data) (log_domain, data, length);
+}

libfprint/fpi-log.h

@@ -1,6 +1,7 @@
 /*
  * Copyright (C) 2007-2008 Daniel Drake <dsd@gentoo.org>
  * Copyright (C) 2018 Bastien Nocera <hadess@hadess.net>
+ * Copyright (C) 2026 Marco Trevisan (Treviño) <mail@3v1n0.net>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -96,3 +97,30 @@
  * Same as BUG_ON() but is always true.
  */
 #define BUG() BUG_ON (1)
+
+void (fpi_dbg_hex_dump_data) (const gchar  *log_domain,
+                              const guint8 *buf,
+                              gsize len);
+
+/**
+ * fp_dbg_hex_dump_data:
+ * @buf: Bytes buffer to dump
+ * @len: Length of @buf to dump
+ *
+ * Prints hex dump of @buf to fp_dbg()
+ */
+#define fp_dbg_hex_dump_data(buf, len) \
+  (fpi_dbg_hex_dump_data) (G_LOG_DOMAIN, (buf), (len))
+
+void (fpi_dbg_hex_dump_bytes) (const gchar *log_domain,
+                               GBytes      *bytes);
+
+/**
+ * fp_dbg_hex_dump_bytes:
+ * @bytes: #GBytes to dump
+ *
+ * Prints hex dump of @bytes to fp_dbg()
+ */
+#define fp_dbg_hex_dump_bytes(bytes) \
+  (fpi_dbg_hex_dump_bytes) \
+  (G_LOG_DOMAIN, (bytes))

libfprint/fpi-spi-transfer.c

@@ -18,6 +18,7 @@
  */
 
 #include "fpi-spi-transfer.h"
+#include "fpi-log.h"
 #include <sys/ioctl.h>
 #include <linux/spi/spidev.h>
 #include <errno.h>
@@ -48,27 +49,6 @@ static gsize block_size = 0;
 
 G_DEFINE_BOXED_TYPE (FpiSpiTransfer, fpi_spi_transfer, fpi_spi_transfer_ref, fpi_spi_transfer_unref)
 
-static void
-dump_buffer (guchar *buf, gssize dump_len)
-{
-  g_autoptr(GString) line = NULL;
-
-  line = g_string_new ("");
-  /* Dump the buffer. */
-  for (gssize i = 0; i < dump_len; i++)
-    {
-      g_string_append_printf (line, "%02x ", buf[i]);
-      if ((i + 1) % 16 == 0)
-        {
-          g_debug ("%s", line->str);
-          g_string_set_size (line, 0);
-        }
-    }
-
-  if (line->len)
-    g_debug ("%s", line->str);
-}
-
 static void
 log_transfer (FpiSpiTransfer *transfer, gboolean submit, GError *error)
 {
@@ -82,7 +62,7 @@ log_transfer (FpiSpiTransfer *transfer, gboolean submit, GError *error)
                    transfer->length_rd);
 
           if (transfer->buffer_wr)
-            dump_buffer (transfer->buffer_wr, transfer->length_wr);
+            fp_dbg_hex_dump_data (transfer->buffer_wr, transfer->length_wr);
         }
       else
         {
@@ -98,7 +78,7 @@ log_transfer (FpiSpiTransfer *transfer, gboolean submit, GError *error)
                    transfer->length_wr,
                    transfer->length_rd);
           if (transfer->buffer_rd)
-            dump_buffer (transfer->buffer_rd, transfer->length_rd);
+            fp_dbg_hex_dump_data (transfer->buffer_rd, transfer->length_rd);
         }
     }
 }

libfprint/fpi-usb-transfer.c

@@ -65,25 +65,9 @@ log_transfer (FpiUsbTransfer *transfer, gboolean submit, GError *error)
 
       if (!submit == !!(transfer->endpoint & FPI_USB_ENDPOINT_IN))
         {
-          g_autoptr(GString) line = NULL;
+          fp_dbg_hex_dump_data (transfer->buffer,
-          gssize dump_len;
+                                (transfer->endpoint & FPI_USB_ENDPOINT_IN) ?
-
+                                transfer->actual_length : transfer->length);
-          dump_len = (transfer->endpoint & FPI_USB_ENDPOINT_IN) ? transfer->actual_length : transfer->length;
-
-          line = g_string_new ("");
-          /* Dump the buffer. */
-          for (gint i = 0; i < dump_len; i++)
-            {
-              g_string_append_printf (line, "%02x ", transfer->buffer[i]);
-              if ((i + 1) % 16 == 0)
-                {
-                  g_debug ("%s", line->str);
-                  g_string_set_size (line, 0);
-                }
-            }
-
-          if (line->len)
-            g_debug ("%s", line->str);
         }
     }
 }

libfprint/meson.build

@@ -21,6 +21,7 @@ libfprint_private_sources = [
     'fpi-device.c',
     'fpi-image-device.c',
     'fpi-image.c',
+    'fpi-log.c',
     'fpi-print.c',
     'fpi-ssm.c',
     'fpi-usb-transfer.c',