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iobuffer.c
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/
iobuffer.c
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//
// iobuffer.c
// couchstore
//
// Created by Jens Alfke on 4/12/12.
// Copyright (c) 2012 Couchbase, Inc. All rights reserved.
//
#include "config.h"
#include "iobuffer.h"
#include "internal.h"
#include <stdlib.h>
#include <string.h>
#define LOG_BUFFER 0 && defined(DEBUG)
#if LOG_BUFFER
#include <stdio.h>
#endif
#define MAX_READ_BUFFERS 8
#define WRITE_BUFFER_CAPACITY (128*1024)
#define READ_BUFFER_CAPACITY (8*1024)
#ifdef min
#undef min
#endif
static inline ssize_t min(ssize_t a, ssize_t b) {return a < b ? a : b;}
typedef struct file_buffer {
struct file_buffer* prev;
struct file_buffer* next;
struct buffered_file_handle *owner;
size_t capacity;
size_t length;
off_t offset;
uint8_t dirty;
uint8_t bytes[1];
} file_buffer;
// How I interpret a couch_file_handle:
typedef struct buffered_file_handle {
const couch_file_ops* raw_ops;
couch_file_handle raw_ops_handle;
unsigned nbuffers;
file_buffer* write_buffer;
file_buffer* first_buffer;
} buffered_file_handle;
static file_buffer* new_buffer(buffered_file_handle* owner, size_t capacity) {
file_buffer *buf = malloc(sizeof(file_buffer) + capacity);
if (buf) {
buf->prev = buf->next = NULL;
buf->owner = owner;
buf->capacity = capacity;
buf->length = 0;
buf->offset = 0;
buf->dirty = 0;
}
#if LOG_BUFFER
fprintf(stderr, "BUFFER: %p <- new_buffer(%zu)\n", buf, capacity);
#endif
return buf;
}
static void free_buffer(file_buffer* buf) {
#if LOG_BUFFER
fprintf(stderr, "BUFFER: %p freed\n", buf);
#endif
free(buf);
}
//////// BUFFER WRITES:
// Write as many bytes as possible into the buffer, returning the count
static size_t write_to_buffer(file_buffer* buf, const void *bytes, size_t nbyte, off_t offset)
{
if (buf->length == 0) {
// If buffer is empty, align it to start at the current offset:
buf->offset = offset;
} else if (offset < buf->offset || offset > buf->offset + (off_t)buf->length) {
// If it's out of range, don't write anything
return 0;
}
size_t offset_in_buffer = (size_t)(offset - buf->offset);
size_t buffer_nbyte = min(buf->capacity - offset_in_buffer, nbyte);
memcpy(buf->bytes + offset_in_buffer, bytes, buffer_nbyte);
buf->dirty = 1;
offset_in_buffer += buffer_nbyte;
if (offset_in_buffer > buf->length)
buf->length = offset_in_buffer;
return buffer_nbyte;
}
// Write the current buffer to disk and empty it.
static couchstore_error_t flush_buffer(file_buffer* buf) {
while (buf->length > 0 && buf->dirty) {
ssize_t raw_written = buf->owner->raw_ops->pwrite(buf->owner->raw_ops_handle, buf->bytes, buf->length, buf->offset);
#if LOG_BUFFER
fprintf(stderr, "BUFFER: %p flush %zd bytes at %zd --> %zd\n",
buf, buf->length, buf->offset, raw_written);
#endif
if (raw_written <= 0)
return (couchstore_error_t) raw_written;
buf->length -= raw_written;
buf->offset += raw_written;
memmove(buf->bytes, buf->bytes + raw_written, buf->length);
}
buf->dirty = 0;
return COUCHSTORE_SUCCESS;
}
//////// BUFFER READS:
static size_t read_from_buffer(file_buffer* buf, void *bytes, size_t nbyte, off_t offset) {
if (offset < buf->offset || offset >= buf->offset + (off_t)buf->length) {
return 0;
}
size_t offset_in_buffer = (size_t)(offset - buf->offset);
size_t buffer_nbyte = min(buf->length - offset_in_buffer, nbyte);
memcpy(bytes, buf->bytes + offset_in_buffer, buffer_nbyte);
return buffer_nbyte;
}
static couchstore_error_t load_buffer_from(file_buffer* buf, off_t offset, size_t nbyte) {
if (buf->dirty) {
// If buffer contains data to be written, flush it first:
couchstore_error_t err = flush_buffer(buf);
if (err < 0) {
return err;
}
}
if (offset < buf->offset || offset + nbyte > buf->offset + buf->capacity) {
// Reset the buffer to empty if it has to move:
buf->offset = offset;
buf->length = 0;
}
// Read data to extend the buffer to its capacity (if possible):
ssize_t bytes_read = buf->owner->raw_ops->pread(buf->owner->raw_ops_handle,
buf->bytes + buf->length,
buf->capacity - buf->length,
buf->offset + buf->length);
#if LOG_BUFFER
fprintf(stderr, "BUFFER: %p loaded %zd bytes from %zd\n", buf, bytes_read, offset + buf->length);
#endif
if (bytes_read < 0) {
return (couchstore_error_t) bytes_read;
}
buf->length += bytes_read;
return COUCHSTORE_SUCCESS;
}
//////// BUFFER MANAGEMENT:
static file_buffer* find_buffer(buffered_file_handle* h, off_t offset) {
offset = offset - offset % READ_BUFFER_CAPACITY;
// Find a buffer for this offset, or use the last one:
file_buffer* buffer = h->first_buffer;
while (buffer->offset != offset && buffer->next != NULL)
buffer = buffer->next;
if (buffer->offset != offset) {
if (h->nbuffers < MAX_READ_BUFFERS) {
// Didn't find a matching one, but we can still create another:
file_buffer* buffer2 = new_buffer(h, READ_BUFFER_CAPACITY);
if (buffer2) {
buffer = buffer2;
++h->nbuffers;
}
} else {
#if LOG_BUFFER
fprintf(stderr, "BUFFER: %p recycled, from %zd to %zd\n", buffer, buffer->offset, offset);
#endif
}
}
if (buffer != h->first_buffer) {
// Move the buffer to the start of the list:
if (buffer->prev) buffer->prev->next = buffer->next;
if (buffer->next) buffer->next->prev = buffer->prev;
buffer->prev = NULL;
h->first_buffer->prev = buffer;
buffer->next = h->first_buffer;
h->first_buffer = buffer;
}
return buffer;
}
//////// FILE API:
static void buffered_destructor(couch_file_handle handle)
{
buffered_file_handle *h = (buffered_file_handle*)handle;
if (!h) {
return;
}
h->raw_ops->destructor(h->raw_ops_handle);
free_buffer(h->write_buffer);
file_buffer* buffer, *next;
for (buffer = h->first_buffer; buffer; buffer = next) {
next = buffer->next;
free_buffer(buffer);
}
free(h);
}
static couch_file_handle buffered_constructor_with_raw_ops(const couch_file_ops* raw_ops)
{
buffered_file_handle *h = malloc(sizeof(buffered_file_handle));
if (h) {
h->raw_ops = raw_ops;
h->raw_ops_handle = raw_ops->constructor(raw_ops->cookie);
h->nbuffers = 1;
h->write_buffer = new_buffer(h, WRITE_BUFFER_CAPACITY);
h->first_buffer = new_buffer(h, READ_BUFFER_CAPACITY);
if (!h->write_buffer || !h->first_buffer) {
buffered_destructor((couch_file_handle)h);
h = NULL;
}
}
return (couch_file_handle) h;
}
static couch_file_handle buffered_constructor(void* cookie)
{
(void) cookie;
return buffered_constructor_with_raw_ops(couchstore_get_default_file_ops());
}
static couchstore_error_t buffered_open(couch_file_handle* handle, const char *path, int oflag)
{
buffered_file_handle *h = (buffered_file_handle*)*handle;
return h->raw_ops->open(&h->raw_ops_handle, path, oflag);
}
static void buffered_close(couch_file_handle handle)
{
buffered_file_handle *h = (buffered_file_handle*)handle;
if (!h) {
return;
}
flush_buffer(h->write_buffer);
h->raw_ops->close(h->raw_ops_handle);
}
static ssize_t buffered_pread(couch_file_handle handle, void *buf, size_t nbyte, off_t offset)
{
#if LOG_BUFFER
//fprintf(stderr, "r");
#endif
buffered_file_handle *h = (buffered_file_handle*)handle;
// Flush the write buffer before trying to read anything:
couchstore_error_t err = flush_buffer(h->write_buffer);
if (err < 0) {
return err;
}
ssize_t total_read = 0;
while (nbyte > 0) {
file_buffer* buffer = find_buffer(h, offset);
// Read as much as we can from the current buffer:
ssize_t nbyte_read = read_from_buffer(buffer, buf, nbyte, offset);
if (nbyte_read == 0) {
/*if (nbyte > buffer->capacity) {
// Remainder won't fit in a single buffer, so just read it directly:
nbyte_read = h->raw_ops->pread(h->raw_ops_handle, buf, nbyte, offset);
if (nbyte_read < 0) {
return nbyte_read;
}
} else*/ {
// Move the buffer to cover the remainder of the data to be read.
off_t block_start = offset - (offset % READ_BUFFER_CAPACITY);
err = load_buffer_from(buffer, block_start, (size_t)(offset + nbyte - block_start));
if (err < 0) {
return err;
}
nbyte_read = read_from_buffer(buffer, buf, nbyte, offset);
if (nbyte_read == 0)
break; // must be at EOF
}
}
buf = (char*)buf + nbyte_read;
nbyte -= nbyte_read;
offset += nbyte_read;
total_read += nbyte_read;
}
return total_read;
}
static ssize_t buffered_pwrite(couch_file_handle handle, const void *buf, size_t nbyte, off_t offset)
{
#if LOG_BUFFER
//fprintf(stderr, "w");
#endif
if (nbyte == 0) {
return 0;
}
buffered_file_handle *h = (buffered_file_handle*)handle;
file_buffer* buffer = h->write_buffer;
// Write data to the current buffer:
size_t nbyte_written = write_to_buffer(buffer, buf, nbyte, offset);
if (nbyte_written > 0) {
buf = (char*)buf + nbyte_written;
offset += nbyte_written;
nbyte -= nbyte_written;
}
// Flush the buffer if it's full, or if it isn't aligned with the current write:
if (buffer->length == buffer->capacity || nbyte_written == 0) {
couchstore_error_t error = flush_buffer(buffer);
if (error < 0)
return error;
}
if (nbyte > 0) {
ssize_t written;
// If the remaining data will fit into the buffer, write it; else write directly:
if (nbyte <= (buffer->capacity - buffer->length)) {
written = write_to_buffer(buffer, buf, nbyte, offset);
} else {
written = h->raw_ops->pwrite(h->raw_ops_handle, buf, nbyte, offset);
#if LOG_BUFFER
fprintf(stderr, "BUFFER: passthru %zd bytes at %zd --> %zd\n",
nbyte, offset, written);
#endif
if (written < 0) {
return written;
}
}
nbyte_written += written;
}
return nbyte_written;
}
static off_t buffered_goto_eof(couch_file_handle handle)
{
buffered_file_handle *h = (buffered_file_handle*)handle;
return h->raw_ops->goto_eof(h->raw_ops_handle);
}
static couchstore_error_t buffered_sync(couch_file_handle handle)
{
buffered_file_handle *h = (buffered_file_handle*)handle;
couchstore_error_t err = flush_buffer(h->write_buffer);
if (err == COUCHSTORE_SUCCESS) {
err = h->raw_ops->sync(h->raw_ops_handle);
}
return err;
}
static const couch_file_ops ops = {
(uint64_t)3,
buffered_constructor,
buffered_open,
buffered_close,
buffered_pread,
buffered_pwrite,
buffered_goto_eof,
buffered_sync,
buffered_destructor,
NULL
};
const couch_file_ops *couch_get_buffered_file_ops(const couch_file_ops* raw_ops,
couch_file_handle* handle)
{
*handle = buffered_constructor_with_raw_ops(raw_ops);
return &ops;
}