/*************************************************************************** * __________ __ ___. * Open \______ \ ____ ____ | | _\_ |__ _______ ___ * Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ / * Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < < * Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \ * \/ \/ \/ \/ \/ * $Id$ * * This is a memory allocator designed to provide reasonable management of free * space and fast access to allocated data. More than one allocator can be used * at a time by initializing multiple contexts. * * Copyright (C) 2009 Andrew Mahone * Copyright (C) 2011 Thomas Martitz * * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY * KIND, either express or implied. * ****************************************************************************/ #include /* for abs() */ #include /* for snprintf() */ #include "buflib.h" #include "string-extra.h" /* strlcpy() */ #include "debug.h" #include "system.h" /* for ALIGN_*() */ /* The main goal of this design is fast fetching of the pointer for a handle. * For that reason, the handles are stored in a table at the end of the buffer * with a fixed address, so that returning the pointer for a handle is a simple * table lookup. To reduce the frequency with which allocated blocks will need * to be moved to free space, allocations grow up in address from the start of * the buffer. The buffer is treated as an array of union buflib_data. Blocks * start with a length marker, which is included in their length. Free blocks * are marked by negative length. Allocated blocks have a positiv length marker, * and additional metadata forllowing that: It follows a pointer * (union buflib_data*) to the corresponding handle table entry. so that it can * be quickly found and updated during compaction. After that follows * the pointer to the struct buflib_callbacks associated with this allocation * (may be NULL). That pointer follows a variable length character array * containing the nul-terminated string identifier of the allocation. After this * array there's a length marker for the length of the character array including * this length marker (counted in n*sizeof(union buflib_data)), which allows * to find the start of the character array (and therefore the start of the * entire block) when only the handle or payload start is known. * * Example: * |<- alloc block #1 ->|<- unalloc block ->|<- alloc block #2 ->|<-handle table->| * |L|H|C|cccc|L2|XXXXXX|-L|YYYYYYYYYYYYYYYY|L|H|C|cc|L2|XXXXXXXXXXXXX|AAA| * * L - length marker (negative if block unallocated) * H - handle table enry pointer * C - pointer to struct buflib_callbacks * c - variable sized string identifier * L2 - second length marker for string identifier * X - actual payload * Y - unallocated space * * A - pointer to start of payload (first X) in the handle table (may be null) * * The blocks can be walked by jumping the abs() of the L length marker, i.e. * union buflib_data* L; * for(L = start; L < end; L += abs(L->val)) { .... } * * * The allocator functions are passed a context struct so that two allocators * can be run, for example, one per core may be used, with convenience wrappers * for the single-allocator case that use a predefined context. */ #define B_ALIGN_DOWN(x) \ ALIGN_DOWN(x, sizeof(union buflib_data)) #define B_ALIGN_UP(x) \ ALIGN_UP(x, sizeof(union buflib_data)) #ifdef DEBUG #include #define BDEBUGF DEBUGF #else #define BDEBUGF(...) do { } while(0) #endif #define IS_MOVABLE(a) (!a[2].ops || a[2].ops->move_callback) static union buflib_data* find_first_free(struct buflib_context *ctx); static union buflib_data* find_block_before(struct buflib_context *ctx, union buflib_data* block, bool is_free); /* Initialize buffer manager */ void buflib_init(struct buflib_context *ctx, void *buf, size_t size) { union buflib_data *bd_buf = buf; /* Align on sizeof(buflib_data), to prevent unaligned access */ ALIGN_BUFFER(bd_buf, size, sizeof(union buflib_data)); size /= sizeof(union buflib_data); /* The handle table is initialized with no entries */ ctx->handle_table = bd_buf + size; ctx->last_handle = bd_buf + size; ctx->first_free_handle = bd_buf + size - 1; ctx->buf_start = bd_buf; /* A marker is needed for the end of allocated data, to make sure that it * does not collide with the handle table, and to detect end-of-buffer. */ ctx->alloc_end = bd_buf; ctx->compact = true; BDEBUGF("buflib initialized with %lu.%2lu kiB", (unsigned long)size / 1024, ((unsigned long)size%1000)/10); } /* Allocate a new handle, returning 0 on failure */ static inline union buflib_data* handle_alloc(struct buflib_context *ctx) { union buflib_data *handle; /* first_free_handle is a lower bound on free handles, work through the * table from there until a handle containing NULL is found, or the end * of the table is reached. */ for (handle = ctx->first_free_handle; handle >= ctx->last_handle; handle--) if (!handle->alloc) break; /* If the search went past the end of the table, it means we need to extend * the table to get a new handle. */ if (handle < ctx->last_handle) { if (handle >= ctx->alloc_end) ctx->last_handle--; else return NULL; } handle->val = -1; return handle; } /* Free one handle, shrinking the handle table if it's the last one */ static inline void handle_free(struct buflib_context *ctx, union buflib_data *handle) { handle->alloc = 0; /* Update free handle lower bound if this handle has a lower index than the * old one. */ if (handle > ctx->first_free_handle) ctx->first_free_handle = handle; if (handle == ctx->last_handle) ctx->last_handle++; else ctx->compact = false; } /* Get the start block of an allocation */ static union buflib_data* handle_to_block(struct buflib_context* ctx, int handle) { union buflib_data* name_field = (union buflib_data*)buflib_get_name(ctx, handle); return name_field - 3; } /* Shrink the handle table, returning true if its size was reduced, false if * not */ static inline bool handle_table_shrink(struct buflib_context *ctx) { bool rv; union buflib_data *handle; for (handle = ctx->last_handle; !(handle->alloc); handle++); if (handle > ctx->first_free_handle) ctx->first_free_handle = handle - 1; rv = handle != ctx->last_handle; ctx->last_handle = handle; return rv; } /* If shift is non-zero, it represents the number of places to move * blocks in memory. Calculate the new address for this block, * update its entry in the handle table, and then move its contents. * * Returns false if moving was unsucessful * (NULL callback or BUFLIB_CB_CANNOT_MOVE was returned) */ static bool move_block(struct buflib_context* ctx, union buflib_data* block, int shift) { char* new_start; union buflib_data *new_block, *tmp = block[1].handle; struct buflib_callbacks *ops = block[2].ops; if (!IS_MOVABLE(block)) return false; int handle = ctx->handle_table - tmp; BDEBUGF("%s(): moving \"%s\"(id=%d) by %d(%d)\n", __func__, block[3].name, handle, shift, shift*(int)sizeof(union buflib_data)); new_block = block + shift; new_start = tmp->alloc + shift*sizeof(union buflib_data); /* If move must be synchronized with use, user should have specified a callback that handles this */ if (ops && ops->sync_callback) ops->sync_callback(handle, true); bool retval = false; if (!ops || ops->move_callback(handle, tmp->alloc, new_start) != BUFLIB_CB_CANNOT_MOVE) { tmp->alloc = new_start; /* update handle table */ memmove(new_block, block, block->val * sizeof(union buflib_data)); retval = true; } if (ops && ops->sync_callback) ops->sync_callback(handle, false); return retval; } /* Compact allocations and handle table, adjusting handle pointers as needed. * Return true if any space was freed or consolidated, false otherwise. */ static bool buflib_compact(struct buflib_context *ctx) { BDEBUGF("%s(): Compacting!\n", __func__); union buflib_data *block, *hole = NULL; int shift = 0, len; /* Store the results of attempting to shrink the handle table */ bool ret = handle_table_shrink(ctx); /* compaction has basically two modes of operation: * 1) the buffer is nicely movable: In this mode, blocks can be simply * moved towards the beginning. Free blocks add to a shift value, * which is the amount to move. * 2) the buffer contains unmovable blocks: unmovable blocks create * holes and reset shift. Once a hole is found, we're trying to fill * holes first, moving by shift is the fallback. As the shift is reset, * this effectively splits the buffer into portions of movable blocks. * This mode cannot be used if no holes are found yet as it only works * when it moves blocks across the portions. On the other side, * moving by shift only works within the same portion * For simplicity only 1 hole at a time is considered */ for(block = find_first_free(ctx); block < ctx->alloc_end; block += len) { bool movable = true; /* cache result to avoid 2nd call to move_block */ len = block->val; /* This block is free, add its length to the shift value */ if (len < 0) { shift += len; len = -len; continue; } /* attempt to fill any hole */ if (hole && -hole->val >= len) { intptr_t hlen = -hole->val; if ((movable = move_block(ctx, block, hole - block))) { ret = true; /* Move was successful. The memory at block is now free */ block->val = -len; /* add its length to shift */ shift += -len; /* Reduce the size of the hole accordingly * but be careful to not overwrite an existing block */ if (hlen != len) { hole += len; hole->val = len - hlen; /* negative */ } else /* hole closed */ hole = NULL; continue; } } /* attempt move the allocation by shift */ if (shift) { union buflib_data* target_block = block + shift; if (!movable || !move_block(ctx, block, shift)) { /* free space before an unmovable block becomes a hole, * therefore mark this block free and track the hole */ target_block->val = shift; hole = target_block; shift = 0; } else ret = true; } } /* Move the end-of-allocation mark, and return true if any new space has * been freed. */ ctx->alloc_end += shift; ctx->compact = true; return ret || shift; } /* Compact the buffer by trying both shrinking and moving. * * Try to move first. If unsuccesfull, try to shrink. If that was successful * try to move once more as there might be more room now. */ static bool buflib_compact_and_shrink(struct buflib_context *ctx, unsigned shrink_hints) { bool result = false; /* if something compacted before already there will be no further gain */ if (!ctx->compact) result = buflib_compact(ctx); if (!result) { union buflib_data *this, *before; for(this = ctx->buf_start, before = this; this < ctx->alloc_end; before = this, this += abs(this->val)) { if (this->val > 0 && this[2].ops && this[2].ops->shrink_callback) { int ret; int handle = ctx->handle_table - this[1].handle; char* data = this[1].handle->alloc; bool last = (this+this->val) == ctx->alloc_end; unsigned pos_hints = shrink_hints & BUFLIB_SHRINK_POS_MASK; /* adjust what we ask for if there's free space in the front * this isn't too unlikely assuming this block is * shrinkable but not movable */ if (pos_hints == BUFLIB_SHRINK_POS_FRONT && before != this && before->val < 0) { size_t free_space = (-before->val) * sizeof(union buflib_data); size_t wanted = shrink_hints & BUFLIB_SHRINK_SIZE_MASK; if (wanted < free_space) /* no shrink needed? */ continue; wanted -= free_space; shrink_hints = pos_hints | wanted; } ret = this[2].ops->shrink_callback(handle, shrink_hints, data, (char*)(this+this->val)-data); result |= (ret == BUFLIB_CB_OK); /* this might have changed in the callback (if * it shrinked from the top), get it again */ this = handle_to_block(ctx, handle); /* could also change with shrinking from back */ if (last) ctx->alloc_end = this + this->val; } } /* shrinking was successful at least once, try compaction again */ if (result) result |= buflib_compact(ctx); } return result; } /* Shift buffered items by size units, and update handle pointers. The shift * value must be determined to be safe *before* calling. */ static void buflib_buffer_shift(struct buflib_context *ctx, int shift) { memmove(ctx->buf_start + shift, ctx->buf_start, (ctx->alloc_end - ctx->buf_start) * sizeof(union buflib_data)); ctx->buf_start += shift; ctx->alloc_end += shift; shift *= sizeof(union buflib_data); union buflib_data *handle; for (handle = ctx->last_handle; handle < ctx->handle_table; handle++) if (handle->alloc) handle->alloc += shift; } /* Shift buffered items up by size bytes, or as many as possible if size == 0. * Set size to the number of bytes freed. */ void* buflib_buffer_out(struct buflib_context *ctx, size_t *size) { if (!ctx->compact) buflib_compact(ctx); size_t avail = ctx->last_handle - ctx->alloc_end; size_t avail_b = avail * sizeof(union buflib_data); if (*size && *size < avail_b) { avail = (*size + sizeof(union buflib_data) - 1) / sizeof(union buflib_data); avail_b = avail * sizeof(union buflib_data); } *size = avail_b; void *ret = ctx->buf_start; buflib_buffer_shift(ctx, avail); return ret; } /* Shift buffered items down by size bytes */ void buflib_buffer_in(struct buflib_context *ctx, int size) { size /= sizeof(union buflib_data); buflib_buffer_shift(ctx, -size); } /* Allocate a buffer of size bytes, returning a handle for it */ int buflib_alloc(struct buflib_context *ctx, size_t size) { return buflib_alloc_ex(ctx, size, "", NULL); } /* Allocate a buffer of size bytes, returning a handle for it. * * The additional name parameter gives the allocation a human-readable name, * the ops parameter points to caller-implemented callbacks for moving and * shrinking. NULL for default callbacks (which do nothing but don't * prevent moving or shrinking) */ int buflib_alloc_ex(struct buflib_context *ctx, size_t size, const char *name, struct buflib_callbacks *ops) { union buflib_data *handle, *block; size_t name_len = name ? B_ALIGN_UP(strlen(name)+1) : 0; bool last; /* This really is assigned a value before use */ int block_len; size += name_len; size = (size + sizeof(union buflib_data) - 1) / sizeof(union buflib_data) /* add 4 objects for alloc len, pointer to handle table entry and * name length, and the ops pointer */ + 4; handle_alloc: handle = handle_alloc(ctx); if (!handle) { /* If allocation has failed, and compaction has succeded, it may be * possible to get a handle by trying again. */ union buflib_data* last_block = find_block_before(ctx, ctx->alloc_end, false); struct buflib_callbacks* ops = last_block[2].ops; unsigned hints = 0; if (!ops || !ops->shrink_callback) { /* the last one isn't shrinkable * make room in front of a shrinkable and move this alloc */ hints = BUFLIB_SHRINK_POS_FRONT; hints |= last_block->val * sizeof(union buflib_data); } else if (ops && ops->shrink_callback) { /* the last is shrinkable, make room for handles directly */ hints = BUFLIB_SHRINK_POS_BACK; hints |= 16*sizeof(union buflib_data); } /* buflib_compact_and_shrink() will compact and move last_block() * if possible */ if (buflib_compact_and_shrink(ctx, hints)) goto handle_alloc; return -1; } buffer_alloc: /* need to re-evaluate last before the loop because the last allocation * possibly made room in its front to fit this, so last would be wrong */ last = false; for (block = find_first_free(ctx);;block += block_len) { /* If the last used block extends all the way to the handle table, the * block "after" it doesn't have a header. Because of this, it's easier * to always find the end of allocation by saving a pointer, and always * calculate the free space at the end by comparing it to the * last_handle pointer. */ if(block == ctx->alloc_end) { last = true; block_len = ctx->last_handle - block; if ((size_t)block_len < size) block = NULL; break; } block_len = block->val; /* blocks with positive length are already allocated. */ if(block_len > 0) continue; block_len = -block_len; /* The search is first-fit, any fragmentation this causes will be * handled at compaction. */ if ((size_t)block_len >= size) break; } if (!block) { /* Try compacting if allocation failed */ unsigned hint = BUFLIB_SHRINK_POS_FRONT | ((size*sizeof(union buflib_data))&BUFLIB_SHRINK_SIZE_MASK); if (buflib_compact_and_shrink(ctx, hint)) { goto buffer_alloc; } else { handle->val=1; handle_free(ctx, handle); return -2; } } /* Set up the allocated block, by marking the size allocated, and storing * a pointer to the handle. */ union buflib_data *name_len_slot; block->val = size; block[1].handle = handle; block[2].ops = ops; strcpy(block[3].name, name); name_len_slot = (union buflib_data*)B_ALIGN_UP(block[3].name + name_len); name_len_slot->val = 1 + name_len/sizeof(union buflib_data); handle->alloc = (char*)(name_len_slot + 1); block += size; /* alloc_end must be kept current if we're taking the last block. */ if (last) ctx->alloc_end = block; /* Only free blocks *before* alloc_end have tagged length. */ else if ((size_t)block_len > size) block->val = size - block_len; /* Return the handle index as a positive integer. */ return ctx->handle_table - handle; } static union buflib_data* find_first_free(struct buflib_context *ctx) { union buflib_data* ret = ctx->buf_start; while(ret < ctx->alloc_end) { if (ret->val < 0) break; ret += ret->val; } /* ret is now either a free block or the same as alloc_end, both is fine */ return ret; } /* Finds the free block before block, and returns NULL if it's not free */ static union buflib_data* find_block_before(struct buflib_context *ctx, union buflib_data* block, bool is_free) { union buflib_data *ret = ctx->buf_start, *next_block = ret; /* find the block that's before the current one */ while (next_block < block) { ret = next_block; next_block += abs(ret->val); } /* If next_block == block, the above loop didn't go anywhere. If it did, * and the block before this one is empty, that is the wanted one */ if (next_block == block && ret < block) { if (is_free && ret->val >= 0) /* NULL if found block isn't free */ return NULL; return ret; } return NULL; } /* Free the buffer associated with handle_num. */ int buflib_free(struct buflib_context *ctx, int handle_num) { union buflib_data *handle = ctx->handle_table - handle_num, *freed_block = handle_to_block(ctx, handle_num), *block, *next_block; /* We need to find the block before the current one, to see if it is free * and can be merged with this one. */ block = find_block_before(ctx, freed_block, true); if (block) { block->val -= freed_block->val; } else { /* Otherwise, set block to the newly-freed block, and mark it free, before * continuing on, since the code below exects block to point to a free * block which may have free space after it. */ block = freed_block; block->val = -block->val; } next_block = block - block->val; /* Check if we are merging with the free space at alloc_end. */ if (next_block == ctx->alloc_end) ctx->alloc_end = block; /* Otherwise, the next block might still be a "normal" free block, and the * mid-allocation free means that the buffer is no longer compact. */ else { ctx->compact = false; if (next_block->val < 0) block->val += next_block->val; } handle_free(ctx, handle); handle->alloc = NULL; return 0; /* unconditionally */ } static size_t free_space_at_end(struct buflib_context* ctx) { /* subtract 5 elements for * val, handle, name_len, ops and the handle table entry*/ ptrdiff_t diff = (ctx->last_handle - ctx->alloc_end - 5); diff -= 16; /* space for future handles */ diff *= sizeof(union buflib_data); /* make it bytes */ diff -= 16; /* reserve 16 for the name */ if (diff > 0) return diff; else return 0; } /* Return the maximum allocatable memory in bytes */ size_t buflib_available(struct buflib_context* ctx) { union buflib_data *this; size_t free_space = 0, max_free_space = 0; /* make sure buffer is as contiguous as possible */ if (!ctx->compact) buflib_compact(ctx); /* now look if there's free in holes */ for(this = find_first_free(ctx); this < ctx->alloc_end; this += abs(this->val)) { if (this->val < 0) { free_space += -this->val; continue; } /* an unmovable section resets the count as free space * can't be contigous */ if (!IS_MOVABLE(this)) { if (max_free_space < free_space) max_free_space = free_space; free_space = 0; } } /* select the best */ max_free_space = MAX(max_free_space, free_space); max_free_space *= sizeof(union buflib_data); max_free_space = MAX(max_free_space, free_space_at_end(ctx)); if (max_free_space > 0) return max_free_space; else return 0; } /* * Allocate all available (as returned by buflib_available()) memory and return * a handle to it * * This grabs a lock which can only be unlocked by buflib_free() or * buflib_shrink(), to protect from further allocations (which couldn't be * serviced anyway). */ int buflib_alloc_maximum(struct buflib_context* ctx, const char* name, size_t *size, struct buflib_callbacks *ops) { /* limit name to 16 since that's what buflib_available() accounts for it */ char buf[16]; *size = buflib_available(ctx); if (*size <= 0) /* OOM */ return -1; strlcpy(buf, name, sizeof(buf)); return buflib_alloc_ex(ctx, *size, buf, ops); } /* Shrink the allocation indicated by the handle according to new_start and * new_size. Grow is not possible, therefore new_start and new_start + new_size * must be within the original allocation */ bool buflib_shrink(struct buflib_context* ctx, int handle, void* new_start, size_t new_size) { char* oldstart = buflib_get_data(ctx, handle); char* newstart = new_start; char* newend = newstart + new_size; /* newstart must be higher and new_size not "negative" */ if (newstart < oldstart || newend < newstart) return false; union buflib_data *block = handle_to_block(ctx, handle), *old_next_block = block + block->val, /* newstart isn't necessarily properly aligned but it * needn't be since it's only dereferenced by the user code */ *aligned_newstart = (union buflib_data*)B_ALIGN_DOWN(newstart), *aligned_oldstart = (union buflib_data*)B_ALIGN_DOWN(oldstart), *new_next_block = (union buflib_data*)B_ALIGN_UP(newend), *new_block, metadata_size; /* growing is not supported */ if (new_next_block > old_next_block) return false; metadata_size.val = aligned_oldstart - block; /* update val and the handle table entry */ new_block = aligned_newstart - metadata_size.val; block[0].val = new_next_block - new_block; block[1].handle->alloc = newstart; if (block != new_block) { /* move metadata over, i.e. pointer to handle table entry and name * This is actually the point of no return. Data in the allocation is * being modified, and therefore we must successfully finish the shrink * operation */ memmove(new_block, block, metadata_size.val*sizeof(metadata_size)); /* mark the old block unallocated */ block->val = block - new_block; /* find the block before in order to merge with the new free space */ union buflib_data *free_before = find_block_before(ctx, block, true); if (free_before) free_before->val += block->val; /* We didn't handle size changes yet, assign block to the new one * the code below the wants block whether it changed or not */ block = new_block; } /* Now deal with size changes that create free blocks after the allocation */ if (old_next_block != new_next_block) { if (ctx->alloc_end == old_next_block) ctx->alloc_end = new_next_block; else if (old_next_block->val < 0) { /* enlarge next block by moving it up */ new_next_block->val = old_next_block->val - (old_next_block - new_next_block); } else if (old_next_block != new_next_block) { /* creating a hole */ /* must be negative to indicate being unallocated */ new_next_block->val = new_next_block - old_next_block; } } return true; } const char* buflib_get_name(struct buflib_context *ctx, int handle) { union buflib_data *data = ALIGN_DOWN(buflib_get_data(ctx, handle), sizeof (*data)); size_t len = data[-1].val; if (len <= 1) return NULL; return data[-len].name; } #ifdef BUFLIB_DEBUG_BLOCKS void buflib_print_allocs(struct buflib_context *ctx, void (*print)(int, const char*)) { union buflib_data *this, *end = ctx->handle_table; char buf[128]; for(this = end - 1; this >= ctx->last_handle; this--) { if (!this->alloc) continue; int handle_num; const char *name; union buflib_data *block_start, *alloc_start; intptr_t alloc_len; handle_num = end - this; alloc_start = buflib_get_data(ctx, handle_num); name = buflib_get_name(ctx, handle_num); block_start = (union buflib_data*)name - 3; alloc_len = block_start->val * sizeof(union buflib_data); snprintf(buf, sizeof(buf), "%s(%d):\t%p\n" " \t%p\n" " \t%ld\n", name?:"(null)", handle_num, block_start, alloc_start, alloc_len); /* handle_num is 1-based */ print(handle_num - 1, buf); } } void buflib_print_blocks(struct buflib_context *ctx, void (*print)(int, const char*)) { char buf[128]; int i = 0; for(union buflib_data* this = ctx->buf_start; this < ctx->alloc_end; this += abs(this->val)) { snprintf(buf, sizeof(buf), "%8p: val: %4ld (%s)", this, this->val, this->val > 0? this[3].name:""); print(i++, buf); } } #endif #ifdef BUFLIB_DEBUG_BLOCK_SINGLE int buflib_get_num_blocks(struct buflib_context *ctx) { int i = 0; for(union buflib_data* this = ctx->buf_start; this < ctx->alloc_end; this += abs(this->val)) { i++; } return i; } void buflib_print_block_at(struct buflib_context *ctx, int block_num, char* buf, size_t bufsize) { union buflib_data* this = ctx->buf_start; while(block_num > 0 && this < ctx->alloc_end) { this += abs(this->val); block_num -= 1; } snprintf(buf, bufsize, "%8p: val: %4ld (%s)", this, (long)this->val, this->val > 0? this[3].name:""); } #endif