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![Elijah Newren](/assets/img/avatar_default.png)
A typical memory type, such as strbuf, hashmap, or string_list can be stored on the stack or embedded within another structure. mem_pool cannot be, because of how mem_pool_init() and mem_pool_discard() are written. mem_pool_init() does essentially the following (simplified for purposes of explanation here): void mem_pool_init(struct mem_pool **pool...) { *pool = xcalloc(1, sizeof(*pool)); It seems weird to require that mem_pools can only be accessed through a pointer. It also seems slightly dangerous: unlike strbuf_release() or strbuf_reset() or string_list_clear(), all of which put the data structure into a state where it can be re-used after the call, mem_pool_discard(pool) will leave pool pointing at free'd memory. read-cache (and split-index) are the only current users of mem_pools, and they haven't fallen into a use-after-free mistake here, but it seems likely to be problematic for future users especially since several of the current callers of mem_pool_init() will only call it when the mem_pool* is not already allocated (i.e. is NULL). This type of mechanism also prevents finding synchronization points where one can free existing memory and then resume more operations. It would be natural at such points to run something like mem_pool_discard(pool...); and, if necessary, mem_pool_init(&pool...); and then carry on continuing to use the pool. However, this fails badly if several objects had a copy of the value of pool from before these commands; in such a case, those objects won't get the updated value of pool that mem_pool_init() overwrites pool with and they'll all instead be reading and writing from free'd memory. Modify mem_pool_init()/mem_pool_discard() to behave more like strbuf_init()/strbuf_release() or string_list_init()/string_list_clear() In particular: (1) make mem_pool_init() just take a mem_pool* and have it only worry about allocating struct mp_blocks, not the struct mem_pool itself, (2) make mem_pool_discard() free the memory that the pool was responsible for, but leave it in a state where it can be used to allocate more memory afterward (without the need to call mem_pool_init() again). Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
476 lines
14 KiB
C
476 lines
14 KiB
C
#include "cache.h"
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#include "split-index.h"
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#include "ewah/ewok.h"
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struct split_index *init_split_index(struct index_state *istate)
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{
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if (!istate->split_index) {
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istate->split_index = xcalloc(1, sizeof(*istate->split_index));
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istate->split_index->refcount = 1;
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}
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return istate->split_index;
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}
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int read_link_extension(struct index_state *istate,
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const void *data_, unsigned long sz)
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{
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const unsigned char *data = data_;
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struct split_index *si;
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int ret;
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if (sz < the_hash_algo->rawsz)
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return error("corrupt link extension (too short)");
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si = init_split_index(istate);
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hashcpy(si->base_oid.hash, data);
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data += the_hash_algo->rawsz;
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sz -= the_hash_algo->rawsz;
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if (!sz)
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return 0;
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si->delete_bitmap = ewah_new();
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ret = ewah_read_mmap(si->delete_bitmap, data, sz);
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if (ret < 0)
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return error("corrupt delete bitmap in link extension");
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data += ret;
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sz -= ret;
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si->replace_bitmap = ewah_new();
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ret = ewah_read_mmap(si->replace_bitmap, data, sz);
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if (ret < 0)
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return error("corrupt replace bitmap in link extension");
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if (ret != sz)
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return error("garbage at the end of link extension");
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return 0;
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}
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int write_link_extension(struct strbuf *sb,
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struct index_state *istate)
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{
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struct split_index *si = istate->split_index;
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strbuf_add(sb, si->base_oid.hash, the_hash_algo->rawsz);
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if (!si->delete_bitmap && !si->replace_bitmap)
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return 0;
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ewah_serialize_strbuf(si->delete_bitmap, sb);
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ewah_serialize_strbuf(si->replace_bitmap, sb);
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return 0;
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}
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static void mark_base_index_entries(struct index_state *base)
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{
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int i;
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/*
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* To keep track of the shared entries between
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* istate->base->cache[] and istate->cache[], base entry
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* position is stored in each base entry. All positions start
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* from 1 instead of 0, which is reserved to say "this is a new
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* entry".
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*/
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for (i = 0; i < base->cache_nr; i++)
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base->cache[i]->index = i + 1;
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}
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void move_cache_to_base_index(struct index_state *istate)
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{
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struct split_index *si = istate->split_index;
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int i;
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/*
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* If there was a previous base index, then transfer ownership of allocated
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* entries to the parent index.
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*/
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if (si->base &&
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si->base->ce_mem_pool) {
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if (!istate->ce_mem_pool) {
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istate->ce_mem_pool = xmalloc(sizeof(struct mem_pool));
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mem_pool_init(istate->ce_mem_pool, 0);
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}
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mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
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}
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si->base = xcalloc(1, sizeof(*si->base));
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si->base->version = istate->version;
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/* zero timestamp disables racy test in ce_write_index() */
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si->base->timestamp = istate->timestamp;
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ALLOC_GROW(si->base->cache, istate->cache_nr, si->base->cache_alloc);
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si->base->cache_nr = istate->cache_nr;
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/*
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* The mem_pool needs to move with the allocated entries.
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*/
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si->base->ce_mem_pool = istate->ce_mem_pool;
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istate->ce_mem_pool = NULL;
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COPY_ARRAY(si->base->cache, istate->cache, istate->cache_nr);
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mark_base_index_entries(si->base);
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for (i = 0; i < si->base->cache_nr; i++)
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si->base->cache[i]->ce_flags &= ~CE_UPDATE_IN_BASE;
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}
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static void mark_entry_for_delete(size_t pos, void *data)
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{
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struct index_state *istate = data;
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if (pos >= istate->cache_nr)
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die("position for delete %d exceeds base index size %d",
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(int)pos, istate->cache_nr);
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istate->cache[pos]->ce_flags |= CE_REMOVE;
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istate->split_index->nr_deletions++;
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}
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static void replace_entry(size_t pos, void *data)
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{
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struct index_state *istate = data;
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struct split_index *si = istate->split_index;
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struct cache_entry *dst, *src;
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if (pos >= istate->cache_nr)
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die("position for replacement %d exceeds base index size %d",
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(int)pos, istate->cache_nr);
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if (si->nr_replacements >= si->saved_cache_nr)
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die("too many replacements (%d vs %d)",
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si->nr_replacements, si->saved_cache_nr);
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dst = istate->cache[pos];
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if (dst->ce_flags & CE_REMOVE)
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die("entry %d is marked as both replaced and deleted",
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(int)pos);
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src = si->saved_cache[si->nr_replacements];
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if (ce_namelen(src))
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die("corrupt link extension, entry %d should have "
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"zero length name", (int)pos);
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src->index = pos + 1;
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src->ce_flags |= CE_UPDATE_IN_BASE;
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src->ce_namelen = dst->ce_namelen;
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copy_cache_entry(dst, src);
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discard_cache_entry(src);
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si->nr_replacements++;
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}
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void merge_base_index(struct index_state *istate)
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{
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struct split_index *si = istate->split_index;
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unsigned int i;
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mark_base_index_entries(si->base);
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si->saved_cache = istate->cache;
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si->saved_cache_nr = istate->cache_nr;
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istate->cache_nr = si->base->cache_nr;
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istate->cache = NULL;
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istate->cache_alloc = 0;
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ALLOC_GROW(istate->cache, istate->cache_nr, istate->cache_alloc);
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COPY_ARRAY(istate->cache, si->base->cache, istate->cache_nr);
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si->nr_deletions = 0;
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si->nr_replacements = 0;
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ewah_each_bit(si->replace_bitmap, replace_entry, istate);
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ewah_each_bit(si->delete_bitmap, mark_entry_for_delete, istate);
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if (si->nr_deletions)
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remove_marked_cache_entries(istate, 0);
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for (i = si->nr_replacements; i < si->saved_cache_nr; i++) {
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if (!ce_namelen(si->saved_cache[i]))
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die("corrupt link extension, entry %d should "
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"have non-zero length name", i);
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add_index_entry(istate, si->saved_cache[i],
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ADD_CACHE_OK_TO_ADD |
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ADD_CACHE_KEEP_CACHE_TREE |
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/*
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* we may have to replay what
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* merge-recursive.c:update_stages()
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* does, which has this flag on
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*/
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ADD_CACHE_SKIP_DFCHECK);
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si->saved_cache[i] = NULL;
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}
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ewah_free(si->delete_bitmap);
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ewah_free(si->replace_bitmap);
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FREE_AND_NULL(si->saved_cache);
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si->delete_bitmap = NULL;
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si->replace_bitmap = NULL;
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si->saved_cache_nr = 0;
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}
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/*
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* Compare most of the fields in two cache entries, i.e. all except the
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* hashmap_entry and the name.
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*/
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static int compare_ce_content(struct cache_entry *a, struct cache_entry *b)
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{
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const unsigned int ondisk_flags = CE_STAGEMASK | CE_VALID |
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CE_EXTENDED_FLAGS;
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unsigned int ce_flags = a->ce_flags;
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unsigned int base_flags = b->ce_flags;
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int ret;
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/* only on-disk flags matter */
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a->ce_flags &= ondisk_flags;
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b->ce_flags &= ondisk_flags;
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ret = memcmp(&a->ce_stat_data, &b->ce_stat_data,
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offsetof(struct cache_entry, name) -
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offsetof(struct cache_entry, ce_stat_data));
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a->ce_flags = ce_flags;
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b->ce_flags = base_flags;
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return ret;
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}
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void prepare_to_write_split_index(struct index_state *istate)
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{
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struct split_index *si = init_split_index(istate);
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struct cache_entry **entries = NULL, *ce;
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int i, nr_entries = 0, nr_alloc = 0;
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si->delete_bitmap = ewah_new();
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si->replace_bitmap = ewah_new();
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if (si->base) {
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/* Go through istate->cache[] and mark CE_MATCHED to
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* entry with positive index. We'll go through
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* base->cache[] later to delete all entries in base
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* that are not marked with either CE_MATCHED or
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* CE_UPDATE_IN_BASE. If istate->cache[i] is a
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* duplicate, deduplicate it.
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*/
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for (i = 0; i < istate->cache_nr; i++) {
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struct cache_entry *base;
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ce = istate->cache[i];
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if (!ce->index) {
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/*
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* During simple update index operations this
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* is a cache entry that is not present in
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* the shared index. It will be added to the
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* split index.
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*
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* However, it might also represent a file
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* that already has a cache entry in the
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* shared index, but a new index has just
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* been constructed by unpack_trees(), and
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* this entry now refers to different content
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* than what was recorded in the original
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* index, e.g. during 'read-tree -m HEAD^' or
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* 'checkout HEAD^'. In this case the
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* original entry in the shared index will be
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* marked as deleted, and this entry will be
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* added to the split index.
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*/
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continue;
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}
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if (ce->index > si->base->cache_nr) {
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BUG("ce refers to a shared ce at %d, which is beyond the shared index size %d",
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ce->index, si->base->cache_nr);
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}
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ce->ce_flags |= CE_MATCHED; /* or "shared" */
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base = si->base->cache[ce->index - 1];
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if (ce == base) {
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/* The entry is present in the shared index. */
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if (ce->ce_flags & CE_UPDATE_IN_BASE) {
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/*
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* Already marked for inclusion in
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* the split index, either because
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* the corresponding file was
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* modified and the cached stat data
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* was refreshed, or because there
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* is already a replacement entry in
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* the split index.
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* Nothing more to do here.
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*/
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} else if (!ce_uptodate(ce) &&
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is_racy_timestamp(istate, ce)) {
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/*
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* A racily clean cache entry stored
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* only in the shared index: it must
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* be added to the split index, so
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* the subsequent do_write_index()
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* can smudge its stat data.
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*/
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ce->ce_flags |= CE_UPDATE_IN_BASE;
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} else {
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/*
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* The entry is only present in the
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* shared index and it was not
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* refreshed.
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* Just leave it there.
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*/
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}
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continue;
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}
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if (ce->ce_namelen != base->ce_namelen ||
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strcmp(ce->name, base->name)) {
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ce->index = 0;
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continue;
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}
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/*
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* This is the copy of a cache entry that is present
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* in the shared index, created by unpack_trees()
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* while it constructed a new index.
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*/
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if (ce->ce_flags & CE_UPDATE_IN_BASE) {
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/*
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* Already marked for inclusion in the split
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* index, either because the corresponding
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* file was modified and the cached stat data
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* was refreshed, or because the original
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* entry already had a replacement entry in
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* the split index.
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* Nothing to do.
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*/
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} else if (!ce_uptodate(ce) &&
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is_racy_timestamp(istate, ce)) {
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/*
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* A copy of a racily clean cache entry from
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* the shared index. It must be added to
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* the split index, so the subsequent
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* do_write_index() can smudge its stat data.
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*/
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ce->ce_flags |= CE_UPDATE_IN_BASE;
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} else {
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/*
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* Thoroughly compare the cached data to see
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* whether it should be marked for inclusion
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* in the split index.
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*
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* This comparison might be unnecessary, as
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* code paths modifying the cached data do
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* set CE_UPDATE_IN_BASE as well.
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*/
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if (compare_ce_content(ce, base))
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ce->ce_flags |= CE_UPDATE_IN_BASE;
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}
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discard_cache_entry(base);
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si->base->cache[ce->index - 1] = ce;
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}
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for (i = 0; i < si->base->cache_nr; i++) {
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ce = si->base->cache[i];
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if ((ce->ce_flags & CE_REMOVE) ||
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!(ce->ce_flags & CE_MATCHED))
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ewah_set(si->delete_bitmap, i);
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else if (ce->ce_flags & CE_UPDATE_IN_BASE) {
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ewah_set(si->replace_bitmap, i);
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ce->ce_flags |= CE_STRIP_NAME;
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ALLOC_GROW(entries, nr_entries+1, nr_alloc);
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entries[nr_entries++] = ce;
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}
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if (is_null_oid(&ce->oid))
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istate->drop_cache_tree = 1;
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}
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}
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for (i = 0; i < istate->cache_nr; i++) {
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ce = istate->cache[i];
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if ((!si->base || !ce->index) && !(ce->ce_flags & CE_REMOVE)) {
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assert(!(ce->ce_flags & CE_STRIP_NAME));
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ALLOC_GROW(entries, nr_entries+1, nr_alloc);
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entries[nr_entries++] = ce;
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}
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ce->ce_flags &= ~CE_MATCHED;
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}
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/*
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* take cache[] out temporarily, put entries[] in its place
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* for writing
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*/
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si->saved_cache = istate->cache;
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si->saved_cache_nr = istate->cache_nr;
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istate->cache = entries;
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istate->cache_nr = nr_entries;
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}
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void finish_writing_split_index(struct index_state *istate)
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{
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struct split_index *si = init_split_index(istate);
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ewah_free(si->delete_bitmap);
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ewah_free(si->replace_bitmap);
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si->delete_bitmap = NULL;
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si->replace_bitmap = NULL;
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free(istate->cache);
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istate->cache = si->saved_cache;
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istate->cache_nr = si->saved_cache_nr;
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}
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void discard_split_index(struct index_state *istate)
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{
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struct split_index *si = istate->split_index;
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if (!si)
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return;
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istate->split_index = NULL;
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si->refcount--;
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if (si->refcount)
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return;
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if (si->base) {
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discard_index(si->base);
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free(si->base);
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}
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free(si);
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}
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void save_or_free_index_entry(struct index_state *istate, struct cache_entry *ce)
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{
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if (ce->index &&
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istate->split_index &&
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istate->split_index->base &&
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ce->index <= istate->split_index->base->cache_nr &&
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ce == istate->split_index->base->cache[ce->index - 1])
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ce->ce_flags |= CE_REMOVE;
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else
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discard_cache_entry(ce);
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}
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void replace_index_entry_in_base(struct index_state *istate,
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struct cache_entry *old_entry,
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struct cache_entry *new_entry)
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{
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if (old_entry->index &&
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istate->split_index &&
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istate->split_index->base &&
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old_entry->index <= istate->split_index->base->cache_nr) {
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new_entry->index = old_entry->index;
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if (old_entry != istate->split_index->base->cache[new_entry->index - 1])
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discard_cache_entry(istate->split_index->base->cache[new_entry->index - 1]);
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istate->split_index->base->cache[new_entry->index - 1] = new_entry;
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}
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}
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void add_split_index(struct index_state *istate)
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{
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if (!istate->split_index) {
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init_split_index(istate);
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istate->cache_changed |= SPLIT_INDEX_ORDERED;
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}
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}
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void remove_split_index(struct index_state *istate)
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{
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if (istate->split_index) {
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if (istate->split_index->base) {
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/*
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* When removing the split index, we need to move
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* ownership of the mem_pool associated with the
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* base index to the main index. There may be cache entries
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* allocated from the base's memory pool that are shared with
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* the_index.cache[].
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*/
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mem_pool_combine(istate->ce_mem_pool,
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istate->split_index->base->ce_mem_pool);
|
|
|
|
/*
|
|
* The split index no longer owns the mem_pool backing
|
|
* its cache array. As we are discarding this index,
|
|
* mark the index as having no cache entries, so it
|
|
* will not attempt to clean up the cache entries or
|
|
* validate them.
|
|
*/
|
|
istate->split_index->base->cache_nr = 0;
|
|
}
|
|
|
|
/*
|
|
* We can discard the split index because its
|
|
* memory pool has been incorporated into the
|
|
* memory pool associated with the the_index.
|
|
*/
|
|
discard_split_index(istate);
|
|
|
|
istate->cache_changed |= SOMETHING_CHANGED;
|
|
}
|
|
}
|