loader: create bio_alloc and bio_free for bios bounce buffer

We do have 16KB buffer space defined in pxe.c, move it to bio.c and implement
bio_alloc()/bio_free() interface to make it possible to use this space for
other BIOS calls (notably, from biosdisk.c).

MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D17131

1 files changed, 65 insertions, 0 deletions

diff --git a/stand/i386/libi386/bio.c b/stand/i386/libi386/bio.c
new file mode 100644
index 000000000000..d59a69d1a7ac
--- /dev/null
+++ b/stand/i386/libi386/bio.c
@@ -0,0 +1,65 @@
+/*-
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <stand.h>
+#include "libi386.h"
+
+/*
+ * The idea is borrowed from pxe.c and zfsimpl.c. The original buffer
+ * space in pxe.c was 2x 0x2000. Allocating it from BSS will give us needed
+ * memory below 1MB and usable for real mode calls.
+ *
+ * Note the allocations and frees are to be done in reverse order (LIFO).
+ */
+
+static char bio_buffer[BIO_BUFFER_SIZE];
+static char *bio_buffer_end = bio_buffer + BIO_BUFFER_SIZE;
+static char *bio_buffer_ptr = bio_buffer;
+
+void *
+bio_alloc(size_t size)
+{
+	char *ptr;
+
+	ptr = bio_buffer_ptr;
+	if (ptr + size > bio_buffer_end)
+		return (NULL);
+	bio_buffer_ptr += size;
+
+	return (ptr);
+}
+
+void
+bio_free(void *ptr, size_t size)
+{
+
+	if (ptr == NULL)
+		return;
+
+	bio_buffer_ptr -= size;
+	if (bio_buffer_ptr != ptr)
+		panic("bio_alloc()/bio_free() mismatch\n");
+}