Merge branch '781-inconsistent-buffer-size-description-in-manpage' into 'master'

Resolve "Inconsistent --buffer-size description in manpage"

Closes #781 and #782

See merge request sane-project/backends!857

backend/hp5590.c

@@ -2154,6 +2154,24 @@ sane_read_internal (struct hp5590_scanner * scanner, SANE_Byte * data,
        max_length,
        scanner->transferred_image_size);
 
+  /*
+   * We will truncate down the buffer size to *under* what the
+   * internal USB reading buffer can supply. This will avoid page read issues
+   * at the end of the buffer.
+   *
+   * See: https://gitlab.com/sane-project/backends/-/issues/781
+   *
+   */
+  if (max_length > BULK_READ_PAGE_SIZE * MAX_READ_PAGES)
+    {
+      DBG (DBG_proc, "%s, truncating sane_read buffer from %u to %u\n",
+           __func__,
+           max_length,
+	   BULK_READ_PAGE_SIZE * MAX_READ_PAGES);
+
+      max_length = BULK_READ_PAGE_SIZE * MAX_READ_PAGES;
+    }
+
   SANE_Int length_limited = 0;
   *length = max_length;
   if ((unsigned long long) *length > scanner->transferred_image_size)

backend/hp5590_low.c

@@ -99,9 +99,15 @@ struct usb_in_usb_ctrl_setup {
 #define CORE_FLAG_NOT_READY             1 << 1
 
 /* Bulk transfers are done in pages, below their respective sizes */
+/*
+ * Note that we limit the amount we can supply to sane_read() to avoid
+ * clashes with the size of the internal read buffer.
+ *
+ */
 #define BULK_WRITE_PAGE_SIZE            0x0f000
 #define BULK_READ_PAGE_SIZE             0x10000
-#define ALLOCATE_BULK_READ_PAGES        16      /* 16 * 65536 = 1Mb */
+#define ALLOCATE_BULK_READ_PAGES        17      /* 16 * 65536 = 1Mb */
+#define MAX_READ_PAGES			16	/* maximum that we will return to sane_read() */
 
 /* Structure describing bulk read state, because bulk reads will be done in
  * pages, but function caller uses its own buffer, whose size is certainly