kern/buffer: Add variable sized heap buffer

Add a new variable sized heap buffer type (grub_buffer_t) with simple
operations for appending data, accessing the data and maintaining
a read cursor.

Signed-off-by: Chris Coulson <chris.coulson@canonical.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/Makefile.core.def

@@ -123,6 +123,7 @@ kernel = {
   riscv32_efi_startup = kern/riscv/efi/startup.S;
   riscv64_efi_startup = kern/riscv/efi/startup.S;
 
+  common = kern/buffer.c;
   common = kern/command.c;
   common = kern/corecmd.c;
   common = kern/device.c;

grub-core/kern/buffer.c

@@ -0,0 +1,117 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2021  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB 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 General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/buffer.h>
+#include <grub/err.h>
+#include <grub/misc.h>
+#include <grub/mm.h>
+#include <grub/safemath.h>
+#include <grub/types.h>
+
+grub_buffer_t
+grub_buffer_new (grub_size_t sz)
+{
+  struct grub_buffer *ret;
+
+  ret = (struct grub_buffer *) grub_malloc (sizeof (*ret));
+  if (ret == NULL)
+    return NULL;
+
+  ret->data = (grub_uint8_t *) grub_malloc (sz);
+  if (ret->data == NULL)
+    {
+      grub_free (ret);
+      return NULL;
+    }
+
+  ret->sz = sz;
+  ret->pos = 0;
+  ret->used = 0;
+
+  return ret;
+}
+
+void
+grub_buffer_free (grub_buffer_t buf)
+{
+  grub_free (buf->data);
+  grub_free (buf);
+}
+
+grub_err_t
+grub_buffer_ensure_space (grub_buffer_t buf, grub_size_t req)
+{
+  grub_uint8_t *d;
+  grub_size_t newsz = 1;
+
+  /* Is the current buffer size adequate? */
+  if (buf->sz >= req)
+    return GRUB_ERR_NONE;
+
+  /* Find the smallest power-of-2 size that satisfies the request. */
+  while (newsz < req)
+    {
+      if (newsz == 0)
+	return grub_error (GRUB_ERR_OUT_OF_RANGE,
+			   N_("requested buffer size is too large"));
+      newsz <<= 1;
+    }
+
+  d = (grub_uint8_t *) grub_realloc (buf->data, newsz);
+  if (d == NULL)
+    return grub_errno;
+
+  buf->data = d;
+  buf->sz = newsz;
+
+  return GRUB_ERR_NONE;
+}
+
+void *
+grub_buffer_take_data (grub_buffer_t buf)
+{
+  void *data = buf->data;
+
+  buf->data = NULL;
+  buf->sz = buf->pos = buf->used = 0;
+
+  return data;
+}
+
+void
+grub_buffer_reset (grub_buffer_t buf)
+{
+  buf->pos = buf->used = 0;
+}
+
+grub_err_t
+grub_buffer_advance_read_pos (grub_buffer_t buf, grub_size_t n)
+{
+  grub_size_t newpos;
+
+  if (grub_add (buf->pos, n, &newpos))
+    return grub_error (GRUB_ERR_OUT_OF_RANGE, N_("overflow is detected"));
+
+  if (newpos > buf->used)
+    return grub_error (GRUB_ERR_OUT_OF_RANGE,
+		       N_("new read is position beyond the end of the written data"));
+
+  buf->pos = newpos;
+
+  return GRUB_ERR_NONE;
+}

include/grub/buffer.h

@@ -0,0 +1,144 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2021  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB 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 General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef GRUB_BUFFER_H
+#define GRUB_BUFFER_H	1
+
+#include <grub/err.h>
+#include <grub/misc.h>
+#include <grub/mm.h>
+#include <grub/safemath.h>
+#include <grub/types.h>
+
+struct grub_buffer
+{
+  grub_uint8_t *data;
+  grub_size_t sz;
+  grub_size_t pos;
+  grub_size_t used;
+};
+
+/*
+ * grub_buffer_t represents a simple variable sized byte buffer with
+ * read and write cursors. It currently only implements
+ * functionality required by the only user in GRUB (append byte[s],
+ * peeking data at a specified position and updating the read cursor.
+ * Some things that this doesn't do yet are:
+ * - Reading a portion of the buffer by copying data from the current
+ *   read position in to a caller supplied destination buffer and then
+ *   automatically updating the read cursor.
+ * - Dropping the read part at the start of the buffer when an append
+ *   requires more space.
+ */
+typedef struct grub_buffer *grub_buffer_t;
+
+/* Allocate a new buffer with the specified initial size. */
+extern grub_buffer_t grub_buffer_new (grub_size_t sz);
+
+/* Free the buffer and its resources. */
+extern void grub_buffer_free (grub_buffer_t buf);
+
+/* Return the number of unread bytes in this buffer. */
+static inline grub_size_t
+grub_buffer_get_unread_bytes (grub_buffer_t buf)
+{
+  return buf->used - buf->pos;
+}
+
+/*
+ * Ensure that the buffer size is at least the requested
+ * number of bytes.
+ */
+extern grub_err_t grub_buffer_ensure_space (grub_buffer_t buf, grub_size_t req);
+
+/*
+ * Append the specified number of bytes from the supplied
+ * data to the buffer.
+ */
+static inline grub_err_t
+grub_buffer_append_data (grub_buffer_t buf, const void *data, grub_size_t len)
+{
+  grub_size_t req;
+
+  if (grub_add (buf->used, len, &req))
+    return grub_error (GRUB_ERR_OUT_OF_RANGE, N_("overflow is detected"));
+
+  if (grub_buffer_ensure_space (buf, req) != GRUB_ERR_NONE)
+    return grub_errno;
+
+  grub_memcpy (&buf->data[buf->used], data, len);
+  buf->used = req;
+
+  return GRUB_ERR_NONE;
+}
+
+/* Append the supplied character to the buffer. */
+static inline grub_err_t
+grub_buffer_append_char (grub_buffer_t buf, char c)
+{
+  return grub_buffer_append_data (buf, &c, 1);
+}
+
+/*
+ * Forget and return the underlying data buffer. The caller
+ * becomes the owner of this buffer, and must free it when it
+ * is no longer required.
+ */
+extern void *grub_buffer_take_data (grub_buffer_t buf);
+
+/* Reset this buffer. Note that this does not deallocate any resources. */
+void grub_buffer_reset (grub_buffer_t buf);
+
+/*
+ * Return a pointer to the underlying data buffer at the specified
+ * offset from the current read position. Note that this pointer may
+ * become invalid if the buffer is mutated further.
+ */
+static inline void *
+grub_buffer_peek_data_at (grub_buffer_t buf, grub_size_t off)
+{
+  if (grub_add (buf->pos, off, &off))
+    {
+      grub_error (GRUB_ERR_OUT_OF_RANGE, N_("overflow is detected."));
+      return NULL;
+    }
+
+  if (off >= buf->used)
+    {
+      grub_error (GRUB_ERR_OUT_OF_RANGE, N_("peek out of range"));
+      return NULL;
+    }
+
+  return &buf->data[off];
+}
+
+/*
+ * Return a pointer to the underlying data buffer at the current
+ * read position. Note that this pointer may become invalid if the
+ * buffer is mutated further.
+ */
+static inline void *
+grub_buffer_peek_data (grub_buffer_t buf)
+{
+  return grub_buffer_peek_data_at (buf, 0);
+}
+
+/* Advance the read position by the specified number of bytes. */
+extern grub_err_t grub_buffer_advance_read_pos (grub_buffer_t buf, grub_size_t n);
+
+#endif /* GRUB_BUFFER_H */