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>

include/membuff.h

+/*
+ * 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

lib/Makefile

@@ -74,6 +74,7 @@ obj-y += div64.o
 obj-y += hang.o
 obj-y += linux_compat.o
 obj-y += linux_string.o
+obj-y += membuff.o
 obj-$(CONFIG_REGEX) += slre.o
 obj-y += string.o
 obj-y += time.o

lib/membuff.c

+/*
+ * Copyright (c) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * Copyright (c) 1992 Simon Glass
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <errno.h>
+#include <malloc.h>
+#include "membuff.h"
+
+void membuff_purge(struct membuff *mb)
+{
+	/* set mb->head and mb->tail so the buffers look empty */
+	mb->head = mb->start;
+	mb->tail = mb->start;
+}
+
+static int membuff_putrawflex(struct membuff *mb, int maxlen, bool update,
+			      char ***data, int *offsetp)
+{
+	int len;
+
+	/* always write to 'mb->head' */
+	assert(data && offsetp);
+	*data = &mb->start;
+	*offsetp = mb->head - mb->start;
+
+	/* if there is no buffer, we can do nothing */
+	if (!mb->start)
+		return 0;
+
+	/*
+	 * if head is ahead of tail, we can write from head until the end of
+	 * the buffer
+	 */
+	if (mb->head >= mb->tail) {
+		/* work out how many bytes can fit here */
+		len = mb->end - mb->head - 1;
+		if (maxlen >= 0 && len > maxlen)
+			len = maxlen;
+
+		/* update the head pointer to mark these bytes as written */
+		if (update)
+			mb->head += len;
+
+		/*
+		 * if the tail isn't at start of the buffer, then we can
+		 * write one more byte right at the end
+		 */
+		if ((maxlen < 0 || len < maxlen) && mb->tail != mb->start) {
+			len++;
+			if (update)
+				mb->head = mb->start;
+		}
+
+	/* otherwise now we can write until head almost reaches tail */
+	} else {
+		/* work out how many bytes can fit here */
+		len = mb->tail - mb->head - 1;
+		if (maxlen >= 0 && len > maxlen)
+			len = maxlen;
+
+		/* update the head pointer to mark these bytes as written */
+		if (update)
+			mb->head += len;
+	}
+
+	/* return the number of bytes which can be/must be written */
+	return len;
+}
+
+int membuff_putraw(struct membuff *mb, int maxlen, bool update, char **data)
+{
+	char **datap;
+	int offset;
+	int size;
+
+	size = membuff_putrawflex(mb, maxlen, update, &datap, &offset);
+	*data = *datap + offset;
+
+	return size;
+}
+
+bool membuff_putbyte(struct membuff *mb, int ch)
+{
+	char *data;
+
+	if (membuff_putraw(mb, 1, true, &data) != 1)
+		return false;
+	*data = ch;
+
+	return true;
+}
+
+int membuff_getraw(struct membuff *mb, int maxlen, bool update, char **data)
+{
+	int len;
+
+	/* assume for now there is no data to get */
+	len = 0;
+
+	/*
+	 * in this case head is ahead of tail, so we must return data between
+	 *'tail' and 'head'
+	 */
+	if (mb->head > mb->tail) {
+		/* work out the amount of data */
+		*data = mb->tail;
+		len = mb->head - mb->tail;
+
+		/* check it isn't too much */
+		if (maxlen >= 0 && len > maxlen)
+			len = maxlen;
+
+		/* & mark it as read from the buffer */
+		if (update)
+			mb->tail += len;
+	}
+
+	/*
+	 * if head is before tail, then we have data between 'tail' and 'end'
+	 * and some more data between 'start' and 'head'(which we can't
+	 * return this time
+	 */
+	else if (mb->head < mb->tail) {
+		/* work out the amount of data */
+		*data = mb->tail;
+		len = mb->end - mb->tail;
+		if (maxlen >= 0 && len > maxlen)
+			len = maxlen;
+		if (update) {
+			mb->tail += len;
+			if (mb->tail == mb->end)
+				mb->tail = mb->start;
+		}
+	}
+
+	debug("getraw: maxlen=%d, update=%d, head=%d, tail=%d, data=%d, len=%d",
+	      maxlen, update, (int)(mb->head - mb->start),
+	      (int)(mb->tail - mb->start), (int)(*data - mb->start), len);
+
+	/* return the number of bytes we found */
+	return len;
+}
+
+int membuff_getbyte(struct membuff *mb)
+{
+	char *data = 0;
+
+	return membuff_getraw(mb, 1, true, &data) != 1 ? -1 : *(uint8_t *)data;
+}
+
+int membuff_peekbyte(struct membuff *mb)
+{
+	char *data = 0;
+
+	return membuff_getraw(mb, 1, false, &data) != 1 ? -1 : *(uint8_t *)data;
+}
+
+int membuff_get(struct membuff *mb, char *buff, int maxlen)
+{
+	char *data = 0, *buffptr = buff;
+	int len = 1, i;
+
+	/*
+	 * do this in up to two lots(see GetRaw for why) stopping when there
+	 * is no more data
+	 */
+	for (i = 0; len && i < 2; i++) {
+		/* get a pointer to the data available */
+		len = membuff_getraw(mb, maxlen, true, &data);
+
+		/* copy it into the buffer */
+		memcpy(buffptr, data, len);
+		buffptr += len;
+		maxlen -= len;
+	}
+
+	/* return the number of bytes read */
+	return buffptr - buff;
+}
+
+int membuff_put(struct membuff *mb, const char *buff, int length)
+{
+	char *data;
+	int towrite, i, written;
+
+	for (i = written = 0; i < 2; i++) {
+		/* ask where some data can be written */
+		towrite = membuff_putraw(mb, length, true, &data);
+
+		/* and write it, updating the bytes length */
+		memcpy(data, buff, towrite);
+		written += towrite;
+		buff += towrite;
+		length -= towrite;
+	}
+
+	/* return the number of bytes written */
+	return written;
+}
+
+bool membuff_isempty(struct membuff *mb)
+{
+	return mb->head == mb->tail;
+}
+
+int membuff_avail(struct membuff *mb)
+{
+	struct membuff copy;
+	int i, avail;
+	char *data = 0;
+
+	/* make a copy of this buffer's control data */
+	copy = *mb;
+
+	/* now read everything out of the copied buffer */
+	for (i = avail = 0; i < 2; i++)
+		avail += membuff_getraw(&copy, -1, true, &data);
+
+	/* and return how much we read */
+	return avail;
+}
+
+int membuff_size(struct membuff *mb)
+{
+	return mb->end - mb->start;
+}
+
+bool membuff_makecontig(struct membuff *mb)
+{
+	int topsize, botsize;
+
+	debug("makecontig: head=%d, tail=%d, size=%d",
+	      (int)(mb->head - mb->start), (int)(mb->tail - mb->start),
+	      (int)(mb->end - mb->start));
+
+	/*
+	 * first we move anything at the start of the buffer into the correct
+	 * place some way along
+	 */
+	if (mb->tail > mb->head) {
+		/*
+		 * the data is split into two parts, from 0 to ->head and
+		 * from ->tail to ->end. We move the stuff from 0 to ->head
+		 * up to make space for the other data before it
+		 */
+		topsize = mb->end - mb->tail;
+		botsize = mb->head - mb->start;
+
+		/*
+		 * must move data at bottom up by 'topsize' bytes - check if
+		 * there's room
+		 */
+		if (mb->head + topsize >= mb->tail)
+			return false;
+		memmove(mb->start + topsize, mb->start, botsize);
+		debug("	- memmove(%d, %d, %d)", topsize, 0, botsize);
+
+	/* nothing at the start, so skip that step */
+	} else {
+		topsize = mb->head - mb->tail;
+		botsize = 0;
+	}
+
+	/* now move data at top down to the bottom */
+	memcpy(mb->start, mb->tail, topsize);
+	debug("	- memcpy(%d, %d, %d)", 0, (int)(mb->tail - mb->start), topsize);
+
+	/* adjust pointers */
+	mb->tail = mb->start;
+	mb->head = mb->start + topsize + botsize;
+
+	debug("	- head=%d, tail=%d", (int)(mb->head - mb->start),
+	      (int)(mb->tail - mb->start));
+
+	/* all ok */
+	return true;
+}
+
+int membuff_free(struct membuff *mb)
+{
+	return mb->end == mb->start ? 0 :
+			(mb->end - mb->start) - 1 - membuff_avail(mb);
+}
+
+int membuff_readline(struct membuff *mb, char *str, int maxlen, int minch)
+{
+	int len;  /* number of bytes read (!= string length) */
+	char *s, *end;
+	bool ok = false;
+	char *orig = str;
+
+	end = mb->head >= mb->tail ? mb->head : mb->end;
+	for (len = 0, s = mb->tail; s < end && len < maxlen - 1; str++) {
+		*str = *s++;
+		len++;
+		if (*str == '\n' || *str < minch) {
+			ok = true;
+			break;
+		}
+		if (s == end && mb->tail > mb->head) {
+			s = mb->start;
+			end = mb->head;
+		}
+	}
+
+	/* couldn't get the whole string */
+	if (!ok) {
+		if (maxlen)
+			*orig = '\0';
+		return 0;
+	}
+
+	/* terminate the string, update the membuff and return success */
+	*str = '\0';
+	mb->tail = s == mb->end ? mb->start : s;
+
+	return len;
+}
+
+int membuff_extend_by(struct membuff *mb, int by, int max)
+{
+	int oldhead, oldtail;
+	int size, orig;
+	char *ptr;
+
+	/* double the buffer size until it is big enough */
+	assert(by >= 0);
+	for (orig = mb->end - mb->start, size = orig; size < orig + by;)
+		size *= 2;
+	if (max != -1)
+		size = min(size, max);
+	by = size - orig;
+
+	/* if we're already at maximum, give up */
+	if (by <= 0)
+		return -E2BIG;
+
+	oldhead = mb->head - mb->start;
+	oldtail = mb->tail - mb->start;
+	ptr = realloc(mb->start, size);
+	if (!ptr)
+		return -ENOMEM;
+	mb->start = ptr;
+	mb->head = mb->start + oldhead;
+	mb->tail = mb->start + oldtail;
+
+	if (mb->head < mb->tail) {
+		memmove(mb->tail + by, mb->tail, orig - oldtail);
+		mb->tail += by;
+	}
+	mb->end = mb->start + size;
+
+	return 0;
+}
+
+void membuff_init(struct membuff *mb, char *buff, int size)
+{
+	mb->start = buff;
+	mb->end = mb->start + size;
+	membuff_purge(mb);
+}
+
+int membuff_new(struct membuff *mb, int size)
+{
+	mb->start = malloc(size);
+	if (!mb->start)
+		return -ENOMEM;
+
+	membuff_init(mb, mb->start, size);
+	return 0;
+}
+
+void membuff_uninit(struct membuff *mb)
+{
+	mb->end = NULL;
+	mb->start = NULL;
+	membuff_purge(mb);
+}
+