Add a circular memory buffer implementation

This will be used to support console recording. It provides for a circular
buffer which can be written at the head and read from the tail. It supports
avoiding data copying by providing raw access to the data.

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

1 files changed, 246 insertions, 0 deletions

diff --git a/include/membuff.h b/include/membuff.h
new file mode 100644
index 0000000000..78918e7264
--- /dev/null
+++ b/include/membuff.h
@@ -0,0 +1,246 @@
+/*
+ * Copyright (c) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * Copyright (c) 1992 Simon Glass
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _MEMBUFF_H
+#define _MEMBUFF_H
+
+/**
+ * @struct membuff: holds the state of a membuff - it is used for input and
+ * output buffers. The buffer extends from @start to (@start + @size - 1).
+ * Data in the buffer extends from @tail to @head: it is written in at
+ * @head and read out from @tail. The membuff is empty when @head == @tail
+ * and full when adding another character would make @head == @tail. We
+ * therefore waste one character in the membuff to avoid having an extra flag
+ * to determine whether (when @head == @tail) the membuff is empty or full.
+ *
+ * xxxxxx  data
+ * ......  empty
+ *
+ * .............xxxxxxxxxxxxxxxx.........................
+ *		^		^
+ *		tail		head
+ *
+ * xxxxxxxxxxxxx................xxxxxxxxxxxxxxxxxxxxxxxxx
+ *		^		^
+ *		head		tail
+ */
+struct membuff {
+	char *start;		/** the start of the buffer */
+	char *end;		/** the end of the buffer (start + length) */
+	char *head;		/** current buffer head */
+	char *tail;		/** current buffer tail */
+};
+
+/**
+ * membuff_purge() - reset a membuff to the empty state
+ *
+ * Initialise head and tail pointers so that the membuff becomes empty.
+ *
+ * @mb: membuff to purge
+ */
+void membuff_purge(struct membuff *mb);
+
+/**
+ * membuff_putraw() - find out where bytes can be written
+ *
+ * Work out where in the membuff some data could be written. Return a pointer
+ * to the address and the number of bytes which can be written there. If
+ * @update is true, the caller must then write the data immediately, since
+ * the membuff is updated as if the write has been done,
+ *
+ * Note that because the spare space in a membuff may not be contiguous, this
+ * function may not return @maxlen even if there is enough space in the
+ * membuff. However, by calling this function twice (with @update == true),
+ * you will get access to all the spare space.
+ *
+ * @mb: membuff to adjust
+ * @maxlen: the number of bytes we want to write
+ * @update: true to update the membuff as if the write happened, false to not
+ * @data: the address data can be written to
+ * @return number of bytes which can be written
+ */
+int membuff_putraw(struct membuff *mb, int maxlen, bool update, char **data);
+
+/**
+ * membuff_getraw() - find and return a pointer to available bytes
+ *
+ * Returns a pointer to any valid input data in the given membuff and
+ * optionally marks it as read. Note that not all input data may not be
+ * returned, since data is not necessarily contiguous in the membuff. However,
+ * if you call this function twice (with @update == true) you are guaranteed
+ * to get all available data, in at most two installments.
+ *
+ * @mb: membuff to adjust
+ * @maxlen: maximum number of bytes to get
+ * @update: true to update the membuff as if the bytes have been read (use
+ * false to check bytes without reading them)
+ * @data: returns address of data in input membuff
+ * @return the number of bytes available at *@data
+ */
+int membuff_getraw(struct membuff *mb, int maxlen, bool update, char **data);
+
+/**
+ * membuff_putbyte() - Writes a byte to a membuff
+ *
+ * @mb: membuff to adjust
+ * @ch: byte to write
+ * @return true on success, false if membuff is full
+ */
+bool membuff_putbyte(struct membuff *mb, int ch);
+
+/**
+ * @mb: membuff to adjust
+ * membuff_getbyte() - Read a byte from the membuff
+ * @return the byte read, or -1 if the membuff is empty
+ */
+int membuff_getbyte(struct membuff *mb);
+
+/**
+ * membuff_peekbyte() - check the next available byte
+ *
+ * Return the next byte which membuff_getbyte() would return, without
+ * removing it from the membuff.
+ *
+ * @mb: membuff to adjust
+ * @return the byte peeked, or -1 if the membuff is empty
+ */
+int membuff_peekbyte(struct membuff *mb);
+
+/**
+ * membuff_get() - get data from a membuff
+ *
+ * Copies any available data (up to @maxlen bytes) to @buff and removes it
+ * from the membuff.
+ *
+ * @mb: membuff to adjust
+ * @Buff: address of membuff to transfer bytes to
+ * @maxlen: maximum number of bytes to read
+ * @return the number of bytes read
+ */
+int membuff_get(struct membuff *mb, char *buff, int maxlen);
+
+/**
+ * membuff_put() - write data to a membuff
+ *
+ * Writes some data to a membuff. Returns the number of bytes added. If this
+ * is less than @lnehgt, then the membuff got full
+ *
+ * @mb: membuff to adjust
+ * @data: the data to write
+ * @length: number of bytes to write from 'data'
+ * @return the number of bytes added
+ */
+int membuff_put(struct membuff *mb, const char *buff, int length);
+
+/**
+ * membuff_isempty() - check if a membuff is empty
+ *
+ * @mb: membuff to check
+ * @return true if empty, else false
+ */
+bool membuff_isempty(struct membuff *mb);
+
+/**
+ * membuff_avail() - check available data in a membuff
+ *
+ * @mb: membuff to check
+ * @return number of bytes of data available
+ */
+int membuff_avail(struct membuff *mb);
+
+/**
+ * membuff_size() - get the size of a membuff
+ *
+ * Note that a membuff can only old data up to one byte less than its size.
+ *
+ * @mb: membuff to check
+ * @return total size
+ */
+int membuff_size(struct membuff *mb);
+
+/**
+ * membuff_makecontig() - adjust all membuff data to be contiguous
+ *
+ * This places all data in a membuff into a single contiguous lump, if
+ * possible
+ *
+ * @mb: membuff to adjust
+ * @return true on success
+ */
+bool membuff_makecontig(struct membuff *mb);
+
+/**
+ * membuff_free() - find the number of bytes that can be written to a membuff
+ *
+ * @mb: membuff to check
+ * @return returns the number of bytes free in a membuff
+ */
+int membuff_free(struct membuff *mb);
+
+/**
+ * membuff_readline() - read a line of text from a membuff
+ *
+ * Reads a line of text of up to 'maxlen' characters from a membuff and puts
+ * it in @str. Any character less than @minch is assumed to be the end of
+ * line character
+ *
+ * @mb: membuff to adjust
+ * @str: Place to put the line
+ * @maxlen: Maximum line length (excluding terminator)
+ * @return number of bytes read (including terminator) if a line has been
+ *	   read, 0 if nothing was there
+ */
+int membuff_readline(struct membuff *mb, char *str, int maxlen, int minch);
+
+/**
+ * membuff_extend_by() - expand a membuff
+ *
+ * Extends a membuff by the given number of bytes
+ *
+ * @mb: membuff to adjust
+ * @by: Number of bytes to increase the size by
+ * @max: Maximum size to allow
+ * @return 0 if the expand succeeded, -ENOMEM if not enough memory, -E2BIG
+ * if the the size would exceed @max
+ */
+int membuff_extend_by(struct membuff *mb, int by, int max);
+
+/**
+ * membuff_init() - set up a new membuff using an existing membuff
+ *
+ * @mb: membuff to set up
+ * @buff: Address of buffer
+ * @size: Size of buffer
+ */
+void membuff_init(struct membuff *mb, char *buff, int size);
+
+/**
+ * membuff_uninit() - clear a membuff so it can no longer be used
+ *
+ * @mb: membuff to uninit
+ */
+void membuff_uninit(struct membuff *mb);
+
+/**
+ * membuff_new() - create a new membuff
+ *
+ * @mb: membuff to init
+ * @size: size of membuff to create
+ * @return 0 if OK, -ENOMEM if out of memory
+ */
+int membuff_new(struct membuff *mb, int size);
+
+/**
+ * membuff_dispose() - free memory allocated to a membuff and uninit it
+ *
+ * @mb: membuff to dispose
+ */
+void membuff_dispose(struct membuff *mb);
+
+#endif