Add support for an owned buffer

When passing a data buffer back from a function, it is not always clear
who owns the buffer, i.e. who is responsible for freeing the memory used.
An example of this is where multiple files are decompressed from the
firmware image, using a temporary buffer for reading (since the
compressed data has to live somewhere) and producing a temporary or
permanent buffer with the resuilts.

Where the firmware image can be memory-mapped, as on x86, the compressed
data does not need to be buffered, but the complexity of having a buffer
which is either allocated or not, makes the code hard to understand.

Introduce a new 'abuf' which supports simple buffer operations:

- encapsulating a buffer and its size
- either allocated with malloc() or not
- able to be reliably freed if necessary
- able to be converted to an allocated buffer if needed

This simple API makes it easier to deal with allocated and memory-mapped
buffers.

Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 159 insertions, 0 deletions

diff --git a/include/abuf.h b/include/abuf.h
new file mode 100644
index 0000000000..d230f72806
--- /dev/null
+++ b/include/abuf.h
@@ -0,0 +1,159 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Handles a buffer that can be allocated and freed
+ *
+ * Copyright 2021 Google LLC
+ * Written by Simon Glass <sjg@chromium.org>
+ */
+
+#ifndef __ABUF_H
+#define __ABUF_H
+
+#include <linux/types.h>
+
+/**
+ * struct abuf - buffer that can be allocated and freed
+ *
+ * This is useful for a block of data which may be allocated with malloc(), or
+ * not, so that it needs to be freed correctly when finished with.
+ *
+ * For now it has a very simple purpose.
+ *
+ * Using memset() to zero all fields is guaranteed to be equivalent to
+ * abuf_init().
+ *
+ * @data: Pointer to data
+ * @size: Size of data in bytes
+ * @alloced: true if allocated with malloc(), so must be freed after use
+ */
+struct abuf {
+	void *data;
+	size_t size;
+	bool alloced;
+};
+
+static inline void *abuf_data(const struct abuf *abuf)
+{
+	return abuf->data;
+}
+
+static inline size_t abuf_size(const struct abuf *abuf)
+{
+	return abuf->size;
+}
+
+/**
+ * abuf_set() - set the (unallocated) data in a buffer
+ *
+ * This simply makes the abuf point to the supplied data, which must be live
+ * for the lifetime of the abuf. It is not alloced.
+ *
+ * Any existing data in the abuf is freed and the alloced member is set to
+ * false.
+ *
+ * @abuf: abuf to adjust
+ * @data: New contents of abuf
+ * @size: New size of abuf
+ */
+void abuf_set(struct abuf *abuf, void *data, size_t size);
+
+/**
+ * abuf_map_sysmem() - calls map_sysmem() to set up an abuf
+ *
+ * This is equivalent to abuf_set(abuf, map_sysmem(addr, size), size)
+ *
+ * Any existing data in the abuf is freed and the alloced member is set to
+ * false.
+ *
+ * @abuf: abuf to adjust
+ * @addr: Address to set the abuf to
+ * @size: New size of abuf
+ */
+void abuf_map_sysmem(struct abuf *abuf, ulong addr, size_t size);
+
+/**
+ * abuf_realloc() - Change the size of a buffer
+ *
+ * This uses realloc() to change the size of the buffer, with the same semantics
+ * as that function. If the abuf is not currently alloced, then it will alloc
+ * it if the size needs to increase (i.e. set the alloced member to true)
+ *
+ * @abuf: abuf to adjust
+ * @new_size: new size in bytes.
+ *	if 0, the abuf is freed
+ *	if greater than the current size, the abuf is extended and the new
+ *	   space is not inited. The alloced member is set to true
+ *	if less than the current size, the abuf is contracted and the data at
+ *	   the end is lost. If @new_size is 0, this sets the alloced member to
+ *	   false
+ * @return true if OK, false if out of memory
+ */
+bool abuf_realloc(struct abuf *abuf, size_t new_size);
+
+/**
+ * abuf_uninit_move() - Return the allocated contents and uninit the abuf
+ *
+ * This returns the abuf data to the caller, allocating it if necessary, so that
+ * the caller receives data that it can be sure will hang around. The caller is
+ * responsible for freeing the data.
+ *
+ * If the abuf has allocated data, it is returned. If the abuf has data but it
+ * is not allocated, then it is first allocated, then returned.
+ *
+ * If the abuf size is 0, this returns NULL
+ *
+ * The abuf is uninited as part of this, except if the allocation fails, in
+ * which NULL is returned and the abuf remains untouched.
+ *
+ * The abuf must be inited before this can be called.
+ *
+ * @abuf: abuf to uninit
+ * @sizep: if non-NULL, returns the size of the returned data
+ * @return data contents, allocated with malloc(), or NULL if the data could not
+ *	be allocated, or the data size is 0
+ */
+void *abuf_uninit_move(struct abuf *abuf, size_t *sizep);
+
+/**
+ * abuf_init_move() - Make abuf take over the management of an allocated region
+ *
+ * After this, @data must not be used. All access must be via the abuf.
+ *
+ * @abuf: abuf to init
+ * @data: Existing allocated buffer to place in the abuf
+ * @size: Size of allocated buffer
+ */
+void abuf_init_move(struct abuf *abuf, void *data, size_t size);
+
+/**
+ * abuf_init_set() - Set up a new abuf
+ *
+ * Inits a new abuf and sets up its (unallocated) data
+ *
+ * @abuf: abuf to set up
+ * @data: New contents of abuf
+ * @size: New size of abuf
+ */
+void abuf_init_set(struct abuf *abuf, void *data, size_t size);
+
+/**
+ * abuf_uninit() - Free any memory used by an abuf
+ *
+ * The buffer must be inited before this can be called.
+ *
+ * @abuf: abuf to uninit
+ */
+void abuf_uninit(struct abuf *abuf);
+
+/**
+ * abuf_init() - Set up a new abuf
+ *
+ * This initially has no data and alloced is set to false. This is equivalent to
+ * setting all fields to 0, e.g. with memset(), so callers can do that instead
+ * if desired.
+ *
+ * @abuf: abuf to set up
+ */
+void abuf_init(struct abuf *abuf);
+
+#endif