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Add a circular memory buffer implementation

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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>
This commit is contained in:
Simon Glass 2015-11-08 23:47:47 -07:00
parent 7d94c49765
commit b7b65090b2
3 changed files with 637 additions and 0 deletions
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246
include/membuff.h Normal file
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@ -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

1
lib/Makefile
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@ -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

390
lib/membuff.c Normal file
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/*
* 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);
}
void membuff_dispose(struct membuff *mb)
{
free(&mb->start);
membuff_uninit(mb);
}