From b7b65090b29e6bc133c7922f8290c1e2f75b064a Mon Sep 17 00:00:00 2001 From: Simon Glass Date: Sun, 8 Nov 2015 23:47:47 -0700 Subject: 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 --- include/membuff.h | 246 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 246 insertions(+) create mode 100644 include/membuff.h (limited to 'include') 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 + * + * 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 -- cgit v1.2.1