Documentation/technical: describe bitmap lookup table extension

[git/debian.git] / split-index.c

#include "cache.h"
#include "split-index.h"
#include "ewah/ewok.h"

struct split_index *init_split_index(struct index_state *istate)
{
        if (!istate->split_index) {
                if (istate->sparse_index)
                        die(_("cannot use split index with a sparse index"));

                CALLOC_ARRAY(istate->split_index, 1);
                istate->split_index->refcount = 1;
        }
        return istate->split_index;
}

int read_link_extension(struct index_state *istate,
                         const void *data_, unsigned long sz)
{
        const unsigned char *data = data_;
        struct split_index *si;
        int ret;

        if (sz < the_hash_algo->rawsz)
                return error("corrupt link extension (too short)");
        si = init_split_index(istate);
        oidread(&si->base_oid, data);
        data += the_hash_algo->rawsz;
        sz -= the_hash_algo->rawsz;
        if (!sz)
                return 0;
        si->delete_bitmap = ewah_new();
        ret = ewah_read_mmap(si->delete_bitmap, data, sz);
        if (ret < 0)
                return error("corrupt delete bitmap in link extension");
        data += ret;
        sz -= ret;
        si->replace_bitmap = ewah_new();
        ret = ewah_read_mmap(si->replace_bitmap, data, sz);
        if (ret < 0)
                return error("corrupt replace bitmap in link extension");
        if (ret != sz)
                return error("garbage at the end of link extension");
        return 0;
}

int write_link_extension(struct strbuf *sb,
                         struct index_state *istate)
{
        struct split_index *si = istate->split_index;
        strbuf_add(sb, si->base_oid.hash, the_hash_algo->rawsz);
        if (!si->delete_bitmap && !si->replace_bitmap)
                return 0;
        ewah_serialize_strbuf(si->delete_bitmap, sb);
        ewah_serialize_strbuf(si->replace_bitmap, sb);
        return 0;
}

static void mark_base_index_entries(struct index_state *base)
{
        int i;
        /*
         * To keep track of the shared entries between
         * istate->base->cache[] and istate->cache[], base entry
         * position is stored in each base entry. All positions start
         * from 1 instead of 0, which is reserved to say "this is a new
         * entry".
         */
        for (i = 0; i < base->cache_nr; i++)
                base->cache[i]->index = i + 1;
}

void move_cache_to_base_index(struct index_state *istate)
{
        struct split_index *si = istate->split_index;
        int i;

        /*
         * If there was a previous base index, then transfer ownership of allocated
         * entries to the parent index.
         */
        if (si->base &&
                si->base->ce_mem_pool) {

                if (!istate->ce_mem_pool) {
                        istate->ce_mem_pool = xmalloc(sizeof(struct mem_pool));
                        mem_pool_init(istate->ce_mem_pool, 0);
                }

                mem_pool_combine(istate->ce_mem_pool, istate->split_index->base->ce_mem_pool);
        }

        CALLOC_ARRAY(si->base, 1);
        si->base->version = istate->version;
        /* zero timestamp disables racy test in ce_write_index() */
        si->base->timestamp = istate->timestamp;
        ALLOC_GROW(si->base->cache, istate->cache_nr, si->base->cache_alloc);
        si->base->cache_nr = istate->cache_nr;

        /*
         * The mem_pool needs to move with the allocated entries.
         */
        si->base->ce_mem_pool = istate->ce_mem_pool;
        istate->ce_mem_pool = NULL;

        COPY_ARRAY(si->base->cache, istate->cache, istate->cache_nr);
        mark_base_index_entries(si->base);
        for (i = 0; i < si->base->cache_nr; i++)
                si->base->cache[i]->ce_flags &= ~CE_UPDATE_IN_BASE;
}

static void mark_entry_for_delete(size_t pos, void *data)
{
        struct index_state *istate = data;
        if (pos >= istate->cache_nr)
                die("position for delete %d exceeds base index size %d",
                    (int)pos, istate->cache_nr);
        istate->cache[pos]->ce_flags |= CE_REMOVE;
        istate->split_index->nr_deletions++;
}

static void replace_entry(size_t pos, void *data)
{
        struct index_state *istate = data;
        struct split_index *si = istate->split_index;
        struct cache_entry *dst, *src;

        if (pos >= istate->cache_nr)
                die("position for replacement %d exceeds base index size %d",
                    (int)pos, istate->cache_nr);
        if (si->nr_replacements >= si->saved_cache_nr)
                die("too many replacements (%d vs %d)",
                    si->nr_replacements, si->saved_cache_nr);
        dst = istate->cache[pos];
        if (dst->ce_flags & CE_REMOVE)
                die("entry %d is marked as both replaced and deleted",
                    (int)pos);
        src = si->saved_cache[si->nr_replacements];
        if (ce_namelen(src))
                die("corrupt link extension, entry %d should have "
                    "zero length name", (int)pos);
        src->index = pos + 1;
        src->ce_flags |= CE_UPDATE_IN_BASE;
        src->ce_namelen = dst->ce_namelen;
        copy_cache_entry(dst, src);
        discard_cache_entry(src);
        si->nr_replacements++;
}

void merge_base_index(struct index_state *istate)
{
        struct split_index *si = istate->split_index;
        unsigned int i;

        mark_base_index_entries(si->base);

        si->saved_cache     = istate->cache;
        si->saved_cache_nr  = istate->cache_nr;
        istate->cache_nr    = si->base->cache_nr;
        istate->cache       = NULL;
        istate->cache_alloc = 0;
        ALLOC_GROW(istate->cache, istate->cache_nr, istate->cache_alloc);
        COPY_ARRAY(istate->cache, si->base->cache, istate->cache_nr);

        si->nr_deletions = 0;
        si->nr_replacements = 0;
        ewah_each_bit(si->replace_bitmap, replace_entry, istate);
        ewah_each_bit(si->delete_bitmap, mark_entry_for_delete, istate);
        if (si->nr_deletions)
                remove_marked_cache_entries(istate, 0);

        for (i = si->nr_replacements; i < si->saved_cache_nr; i++) {
                if (!ce_namelen(si->saved_cache[i]))
                        die("corrupt link extension, entry %d should "
                            "have non-zero length name", i);
                add_index_entry(istate, si->saved_cache[i],
                                ADD_CACHE_OK_TO_ADD |
                                ADD_CACHE_KEEP_CACHE_TREE |
                                /*
                                 * we may have to replay what
                                 * merge-recursive.c:update_stages()
                                 * does, which has this flag on
                                 */
                                ADD_CACHE_SKIP_DFCHECK);
                si->saved_cache[i] = NULL;
        }

        ewah_free(si->delete_bitmap);
        ewah_free(si->replace_bitmap);
        FREE_AND_NULL(si->saved_cache);
        si->delete_bitmap  = NULL;
        si->replace_bitmap = NULL;
        si->saved_cache_nr = 0;
}

/*
 * Compare most of the fields in two cache entries, i.e. all except the
 * hashmap_entry and the name.
 */
static int compare_ce_content(struct cache_entry *a, struct cache_entry *b)
{
        const unsigned int ondisk_flags = CE_STAGEMASK | CE_VALID |
                                          CE_EXTENDED_FLAGS;
        unsigned int ce_flags = a->ce_flags;
        unsigned int base_flags = b->ce_flags;
        int ret;

        /* only on-disk flags matter */
        a->ce_flags &= ondisk_flags;
        b->ce_flags &= ondisk_flags;
        ret = memcmp(&a->ce_stat_data, &b->ce_stat_data,
                     offsetof(struct cache_entry, name) -
                     offsetof(struct cache_entry, oid)) ||
                !oideq(&a->oid, &b->oid);
        a->ce_flags = ce_flags;
        b->ce_flags = base_flags;

        return ret;
}

void prepare_to_write_split_index(struct index_state *istate)
{
        struct split_index *si = init_split_index(istate);
        struct cache_entry **entries = NULL, *ce;
        int i, nr_entries = 0, nr_alloc = 0;

        si->delete_bitmap = ewah_new();
        si->replace_bitmap = ewah_new();

        if (si->base) {
                /* Go through istate->cache[] and mark CE_MATCHED to
                 * entry with positive index. We'll go through
                 * base->cache[] later to delete all entries in base
                 * that are not marked with either CE_MATCHED or
                 * CE_UPDATE_IN_BASE. If istate->cache[i] is a
                 * duplicate, deduplicate it.
                 */
                for (i = 0; i < istate->cache_nr; i++) {
                        struct cache_entry *base;
                        ce = istate->cache[i];
                        if (!ce->index) {
                                /*
                                 * During simple update index operations this
                                 * is a cache entry that is not present in
                                 * the shared index.  It will be added to the
                                 * split index.
                                 *
                                 * However, it might also represent a file
                                 * that already has a cache entry in the
                                 * shared index, but a new index has just
                                 * been constructed by unpack_trees(), and
                                 * this entry now refers to different content
                                 * than what was recorded in the original
                                 * index, e.g. during 'read-tree -m HEAD^' or
                                 * 'checkout HEAD^'.  In this case the
                                 * original entry in the shared index will be
                                 * marked as deleted, and this entry will be
                                 * added to the split index.
                                 */
                                continue;
                        }
                        if (ce->index > si->base->cache_nr) {
                                BUG("ce refers to a shared ce at %d, which is beyond the shared index size %d",
                                    ce->index, si->base->cache_nr);
                        }
                        ce->ce_flags |= CE_MATCHED; /* or "shared" */
                        base = si->base->cache[ce->index - 1];
                        if (ce == base) {
                                /* The entry is present in the shared index. */
                                if (ce->ce_flags & CE_UPDATE_IN_BASE) {
                                        /*
                                         * Already marked for inclusion in
                                         * the split index, either because
                                         * the corresponding file was
                                         * modified and the cached stat data
                                         * was refreshed, or because there
                                         * is already a replacement entry in
                                         * the split index.
                                         * Nothing more to do here.
                                         */
                                } else if (!ce_uptodate(ce) &&
                                           is_racy_timestamp(istate, ce)) {
                                        /*
                                         * A racily clean cache entry stored
                                         * only in the shared index: it must
                                         * be added to the split index, so
                                         * the subsequent do_write_index()
                                         * can smudge its stat data.
                                         */
                                        ce->ce_flags |= CE_UPDATE_IN_BASE;
                                } else {
                                        /*
                                         * The entry is only present in the
                                         * shared index and it was not
                                         * refreshed.
                                         * Just leave it there.
                                         */
                                }
                                continue;
                        }
                        if (ce->ce_namelen != base->ce_namelen ||
                            strcmp(ce->name, base->name)) {
                                ce->index = 0;
                                continue;
                        }
                        /*
                         * This is the copy of a cache entry that is present
                         * in the shared index, created by unpack_trees()
                         * while it constructed a new index.
                         */
                        if (ce->ce_flags & CE_UPDATE_IN_BASE) {
                                /*
                                 * Already marked for inclusion in the split
                                 * index, either because the corresponding
                                 * file was modified and the cached stat data
                                 * was refreshed, or because the original
                                 * entry already had a replacement entry in
                                 * the split index.
                                 * Nothing to do.
                                 */
                        } else if (!ce_uptodate(ce) &&
                                   is_racy_timestamp(istate, ce)) {
                                /*
                                 * A copy of a racily clean cache entry from
                                 * the shared index.  It must be added to
                                 * the split index, so the subsequent
                                 * do_write_index() can smudge its stat data.
                                 */
                                ce->ce_flags |= CE_UPDATE_IN_BASE;
                        } else {
                                /*
                                 * Thoroughly compare the cached data to see
                                 * whether it should be marked for inclusion
                                 * in the split index.
                                 *
                                 * This comparison might be unnecessary, as
                                 * code paths modifying the cached data do
                                 * set CE_UPDATE_IN_BASE as well.
                                 */
                                if (compare_ce_content(ce, base))
                                        ce->ce_flags |= CE_UPDATE_IN_BASE;
                        }
                        discard_cache_entry(base);
                        si->base->cache[ce->index - 1] = ce;
                }
                for (i = 0; i < si->base->cache_nr; i++) {
                        ce = si->base->cache[i];
                        if ((ce->ce_flags & CE_REMOVE) ||
                            !(ce->ce_flags & CE_MATCHED))
                                ewah_set(si->delete_bitmap, i);
                        else if (ce->ce_flags & CE_UPDATE_IN_BASE) {
                                ewah_set(si->replace_bitmap, i);
                                ce->ce_flags |= CE_STRIP_NAME;
                                ALLOC_GROW(entries, nr_entries+1, nr_alloc);
                                entries[nr_entries++] = ce;
                        }
                        if (is_null_oid(&ce->oid))
                                istate->drop_cache_tree = 1;
                }
        }

        for (i = 0; i < istate->cache_nr; i++) {
                ce = istate->cache[i];
                if ((!si->base || !ce->index) && !(ce->ce_flags & CE_REMOVE)) {
                        assert(!(ce->ce_flags & CE_STRIP_NAME));
                        ALLOC_GROW(entries, nr_entries+1, nr_alloc);
                        entries[nr_entries++] = ce;
                }
                ce->ce_flags &= ~CE_MATCHED;
        }

        /*
         * take cache[] out temporarily, put entries[] in its place
         * for writing
         */
        si->saved_cache = istate->cache;
        si->saved_cache_nr = istate->cache_nr;
        istate->cache = entries;
        istate->cache_nr = nr_entries;
}

void finish_writing_split_index(struct index_state *istate)
{
        struct split_index *si = init_split_index(istate);

        ewah_free(si->delete_bitmap);
        ewah_free(si->replace_bitmap);
        si->delete_bitmap = NULL;
        si->replace_bitmap = NULL;
        free(istate->cache);
        istate->cache = si->saved_cache;
        istate->cache_nr = si->saved_cache_nr;
}

void discard_split_index(struct index_state *istate)
{
        struct split_index *si = istate->split_index;
        if (!si)
                return;
        istate->split_index = NULL;
        si->refcount--;
        if (si->refcount)
                return;
        if (si->base) {
                discard_index(si->base);
                free(si->base);
        }
        free(si);
}

void save_or_free_index_entry(struct index_state *istate, struct cache_entry *ce)
{
        if (ce->index &&
            istate->split_index &&
            istate->split_index->base &&
            ce->index <= istate->split_index->base->cache_nr &&
            ce == istate->split_index->base->cache[ce->index - 1])
                ce->ce_flags |= CE_REMOVE;
        else
                discard_cache_entry(ce);
}

void replace_index_entry_in_base(struct index_state *istate,
                                 struct cache_entry *old_entry,
                                 struct cache_entry *new_entry)
{
        if (old_entry->index &&
            istate->split_index &&
            istate->split_index->base &&
            old_entry->index <= istate->split_index->base->cache_nr) {
                new_entry->index = old_entry->index;
                if (old_entry != istate->split_index->base->cache[new_entry->index - 1])
                        discard_cache_entry(istate->split_index->base->cache[new_entry->index - 1]);
                istate->split_index->base->cache[new_entry->index - 1] = new_entry;
        }
}

void add_split_index(struct index_state *istate)
{
        if (!istate->split_index) {
                init_split_index(istate);
                istate->cache_changed |= SPLIT_INDEX_ORDERED;
        }
}

void remove_split_index(struct index_state *istate)
{
        if (istate->split_index) {
                if (istate->split_index->base) {
                        /*
                         * When removing the split index, we need to move
                         * ownership of the mem_pool associated with the
                         * base index to the main index. There may be cache entries
                         * allocated from the base's memory pool that are shared with
                         * the_index.cache[].
                         */
                        mem_pool_combine(istate->ce_mem_pool,
                                         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;
        }
}