/* * L2/refcount table cache for the QCOW2 format * * Copyright (c) 2010 Kevin Wolf <kwolf@redhat.com> * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ #include "block_int.h" #include "qemu-common.h" #include "qcow2.h" #include "trace.h" typedef struct Qcow2CachedTable { void* table; int64_t offset; bool dirty; int cache_hits; int ref; } Qcow2CachedTable; struct Qcow2Cache { Qcow2CachedTable* entries; struct Qcow2Cache* depends; int size; bool depends_on_flush; }; Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables) { BDRVQcowState *s = bs->opaque; Qcow2Cache *c; int i; c = g_malloc0(sizeof(*c)); c->size = num_tables; c->entries = g_malloc0(sizeof(*c->entries) * num_tables); for (i = 0; i < c->size; i++) { c->entries[i].table = qemu_blockalign(bs, s->cluster_size); } return c; } int qcow2_cache_destroy(BlockDriverState* bs, Qcow2Cache *c) { int i; for (i = 0; i < c->size; i++) { assert(c->entries[i].ref == 0); qemu_vfree(c->entries[i].table); } g_free(c->entries); g_free(c); return 0; } static int qcow2_cache_flush_dependency(BlockDriverState *bs, Qcow2Cache *c) { int ret; ret = qcow2_cache_flush(bs, c->depends); if (ret < 0) { return ret; } c->depends = NULL; c->depends_on_flush = false; return 0; } static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i) { BDRVQcowState *s = bs->opaque; int ret = 0; if (!c->entries[i].dirty || !c->entries[i].offset) { return 0; } trace_qcow2_cache_entry_flush(qemu_coroutine_self(), c == s->l2_table_cache, i); if (c->depends) { ret = qcow2_cache_flush_dependency(bs, c); } else if (c->depends_on_flush) { ret = bdrv_flush(bs->file); if (ret >= 0) { c->depends_on_flush = false; } } if (ret < 0) { return ret; } if (c == s->refcount_block_cache) { BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_UPDATE_PART); } else if (c == s->l2_table_cache) { BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE); } ret = bdrv_pwrite(bs->file, c->entries[i].offset, c->entries[i].table, s->cluster_size); if (ret < 0) { return ret; } c->entries[i].dirty = false; return 0; } int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c) { BDRVQcowState *s = bs->opaque; int result = 0; int ret; int i; trace_qcow2_cache_flush(qemu_coroutine_self(), c == s->l2_table_cache); for (i = 0; i < c->size; i++) { ret = qcow2_cache_entry_flush(bs, c, i); if (ret < 0 && result != -ENOSPC) { result = ret; } } if (result == 0) { ret = bdrv_flush(bs->file); if (ret < 0) { result = ret; } } return result; } int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c, Qcow2Cache *dependency) { int ret; if (dependency->depends) { ret = qcow2_cache_flush_dependency(bs, dependency); if (ret < 0) { return ret; } } if (c->depends && (c->depends != dependency)) { ret = qcow2_cache_flush_dependency(bs, c); if (ret < 0) { return ret; } } c->depends = dependency; return 0; } void qcow2_cache_depends_on_flush(Qcow2Cache *c) { c->depends_on_flush = true; } static int qcow2_cache_find_entry_to_replace(Qcow2Cache *c) { int i; int min_count = INT_MAX; int min_index = -1; for (i = 0; i < c->size; i++) { if (c->entries[i].ref) { continue; } if (c->entries[i].cache_hits < min_count) { min_index = i; min_count = c->entries[i].cache_hits; } /* Give newer hits priority */ /* TODO Check how to optimize the replacement strategy */ c->entries[i].cache_hits /= 2; } if (min_index == -1) { /* This can't happen in current synchronous code, but leave the check * here as a reminder for whoever starts using AIO with the cache */ abort(); } return min_index; } static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset, void **table, bool read_from_disk) { BDRVQcowState *s = bs->opaque; int i; int ret; trace_qcow2_cache_get(qemu_coroutine_self(), c == s->l2_table_cache, offset, read_from_disk); /* Check if the table is already cached */ for (i = 0; i < c->size; i++) { if (c->entries[i].offset == offset) { goto found; } } /* If not, write a table back and replace it */ i = qcow2_cache_find_entry_to_replace(c); trace_qcow2_cache_get_replace_entry(qemu_coroutine_self(), c == s->l2_table_cache, i); if (i < 0) { return i; } ret = qcow2_cache_entry_flush(bs, c, i); if (ret < 0) { return ret; } trace_qcow2_cache_get_read(qemu_coroutine_self(), c == s->l2_table_cache, i); c->entries[i].offset = 0; if (read_from_disk) { if (c == s->l2_table_cache) { BLKDBG_EVENT(bs->file, BLKDBG_L2_LOAD); } ret = bdrv_pread(bs->file, offset, c->entries[i].table, s->cluster_size); if (ret < 0) { return ret; } } /* Give the table some hits for the start so that it won't be replaced * immediately. The number 32 is completely arbitrary. */ c->entries[i].cache_hits = 32; c->entries[i].offset = offset; /* And return the right table */ found: c->entries[i].cache_hits++; c->entries[i].ref++; *table = c->entries[i].table; trace_qcow2_cache_get_done(qemu_coroutine_self(), c == s->l2_table_cache, i); return 0; } int qcow2_cache_get(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset, void **table) { return qcow2_cache_do_get(bs, c, offset, table, true); } int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset, void **table) { return qcow2_cache_do_get(bs, c, offset, table, false); } int qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table) { int i; for (i = 0; i < c->size; i++) { if (c->entries[i].table == *table) { goto found; } } return -ENOENT; found: c->entries[i].ref--; *table = NULL; assert(c->entries[i].ref >= 0); return 0; } void qcow2_cache_entry_mark_dirty(Qcow2Cache *c, void *table) { int i; for (i = 0; i < c->size; i++) { if (c->entries[i].table == table) { goto found; } } abort(); found: c->entries[i].dirty = true; }