Squashed 'third_party/git/' content from commit cb71568594

git-subtree-dir: third_party/git
git-subtree-split: cb715685942260375e1eb8153b0768a376e4ece7

1 files changed, 1313 insertions, 0 deletions

diff --git a/notes.c b/notes.c
new file mode 100644
index 000000000000..75c028b3005a
--- /dev/null
+++ b/notes.c
@@ -0,0 +1,1313 @@
+#include "cache.h"
+#include "config.h"
+#include "notes.h"
+#include "object-store.h"
+#include "blob.h"
+#include "tree.h"
+#include "utf8.h"
+#include "strbuf.h"
+#include "tree-walk.h"
+#include "string-list.h"
+#include "refs.h"
+
+/*
+ * Use a non-balancing simple 16-tree structure with struct int_node as
+ * internal nodes, and struct leaf_node as leaf nodes. Each int_node has a
+ * 16-array of pointers to its children.
+ * The bottom 2 bits of each pointer is used to identify the pointer type
+ * - ptr & 3 == 0 - NULL pointer, assert(ptr == NULL)
+ * - ptr & 3 == 1 - pointer to next internal node - cast to struct int_node *
+ * - ptr & 3 == 2 - pointer to note entry - cast to struct leaf_node *
+ * - ptr & 3 == 3 - pointer to subtree entry - cast to struct leaf_node *
+ *
+ * The root node is a statically allocated struct int_node.
+ */
+struct int_node {
+	void *a[16];
+};
+
+/*
+ * Leaf nodes come in two variants, note entries and subtree entries,
+ * distinguished by the LSb of the leaf node pointer (see above).
+ * As a note entry, the key is the SHA1 of the referenced object, and the
+ * value is the SHA1 of the note object.
+ * As a subtree entry, the key is the prefix SHA1 (w/trailing NULs) of the
+ * referenced object, using the last byte of the key to store the length of
+ * the prefix. The value is the SHA1 of the tree object containing the notes
+ * subtree.
+ */
+struct leaf_node {
+	struct object_id key_oid;
+	struct object_id val_oid;
+};
+
+/*
+ * A notes tree may contain entries that are not notes, and that do not follow
+ * the naming conventions of notes. There are typically none/few of these, but
+ * we still need to keep track of them. Keep a simple linked list sorted alpha-
+ * betically on the non-note path. The list is populated when parsing tree
+ * objects in load_subtree(), and the non-notes are correctly written back into
+ * the tree objects produced by write_notes_tree().
+ */
+struct non_note {
+	struct non_note *next; /* grounded (last->next == NULL) */
+	char *path;
+	unsigned int mode;
+	struct object_id oid;
+};
+
+#define PTR_TYPE_NULL     0
+#define PTR_TYPE_INTERNAL 1
+#define PTR_TYPE_NOTE     2
+#define PTR_TYPE_SUBTREE  3
+
+#define GET_PTR_TYPE(ptr)       ((uintptr_t) (ptr) & 3)
+#define CLR_PTR_TYPE(ptr)       ((void *) ((uintptr_t) (ptr) & ~3))
+#define SET_PTR_TYPE(ptr, type) ((void *) ((uintptr_t) (ptr) | (type)))
+
+#define GET_NIBBLE(n, sha1) ((((sha1)[(n) >> 1]) >> ((~(n) & 0x01) << 2)) & 0x0f)
+
+#define KEY_INDEX (the_hash_algo->rawsz - 1)
+#define FANOUT_PATH_SEPARATORS (the_hash_algo->rawsz - 1)
+#define FANOUT_PATH_SEPARATORS_MAX ((GIT_MAX_HEXSZ / 2) - 1)
+#define SUBTREE_SHA1_PREFIXCMP(key_sha1, subtree_sha1) \
+	(memcmp(key_sha1, subtree_sha1, subtree_sha1[KEY_INDEX]))
+
+struct notes_tree default_notes_tree;
+
+static struct string_list display_notes_refs = STRING_LIST_INIT_NODUP;
+static struct notes_tree **display_notes_trees;
+
+static void load_subtree(struct notes_tree *t, struct leaf_node *subtree,
+		struct int_node *node, unsigned int n);
+
+/*
+ * Search the tree until the appropriate location for the given key is found:
+ * 1. Start at the root node, with n = 0
+ * 2. If a[0] at the current level is a matching subtree entry, unpack that
+ *    subtree entry and remove it; restart search at the current level.
+ * 3. Use the nth nibble of the key as an index into a:
+ *    - If a[n] is an int_node, recurse from #2 into that node and increment n
+ *    - If a matching subtree entry, unpack that subtree entry (and remove it);
+ *      restart search at the current level.
+ *    - Otherwise, we have found one of the following:
+ *      - a subtree entry which does not match the key
+ *      - a note entry which may or may not match the key
+ *      - an unused leaf node (NULL)
+ *      In any case, set *tree and *n, and return pointer to the tree location.
+ */
+static void **note_tree_search(struct notes_tree *t, struct int_node **tree,
+		unsigned char *n, const unsigned char *key_sha1)
+{
+	struct leaf_node *l;
+	unsigned char i;
+	void *p = (*tree)->a[0];
+
+	if (GET_PTR_TYPE(p) == PTR_TYPE_SUBTREE) {
+		l = (struct leaf_node *) CLR_PTR_TYPE(p);
+		if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_oid.hash)) {
+			/* unpack tree and resume search */
+			(*tree)->a[0] = NULL;
+			load_subtree(t, l, *tree, *n);
+			free(l);
+			return note_tree_search(t, tree, n, key_sha1);
+		}
+	}
+
+	i = GET_NIBBLE(*n, key_sha1);
+	p = (*tree)->a[i];
+	switch (GET_PTR_TYPE(p)) {
+	case PTR_TYPE_INTERNAL:
+		*tree = CLR_PTR_TYPE(p);
+		(*n)++;
+		return note_tree_search(t, tree, n, key_sha1);
+	case PTR_TYPE_SUBTREE:
+		l = (struct leaf_node *) CLR_PTR_TYPE(p);
+		if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_oid.hash)) {
+			/* unpack tree and resume search */
+			(*tree)->a[i] = NULL;
+			load_subtree(t, l, *tree, *n);
+			free(l);
+			return note_tree_search(t, tree, n, key_sha1);
+		}
+		/* fall through */
+	default:
+		return &((*tree)->a[i]);
+	}
+}
+
+/*
+ * To find a leaf_node:
+ * Search to the tree location appropriate for the given key:
+ * If a note entry with matching key, return the note entry, else return NULL.
+ */
+static struct leaf_node *note_tree_find(struct notes_tree *t,
+		struct int_node *tree, unsigned char n,
+		const unsigned char *key_sha1)
+{
+	void **p = note_tree_search(t, &tree, &n, key_sha1);
+	if (GET_PTR_TYPE(*p) == PTR_TYPE_NOTE) {
+		struct leaf_node *l = (struct leaf_node *) CLR_PTR_TYPE(*p);
+		if (hasheq(key_sha1, l->key_oid.hash))
+			return l;
+	}
+	return NULL;
+}
+
+/*
+ * How to consolidate an int_node:
+ * If there are > 1 non-NULL entries, give up and return non-zero.
+ * Otherwise replace the int_node at the given index in the given parent node
+ * with the only NOTE entry (or a NULL entry if no entries) from the given
+ * tree, and return 0.
+ */
+static int note_tree_consolidate(struct int_node *tree,
+	struct int_node *parent, unsigned char index)
+{
+	unsigned int i;
+	void *p = NULL;
+
+	assert(tree && parent);
+	assert(CLR_PTR_TYPE(parent->a[index]) == tree);
+
+	for (i = 0; i < 16; i++) {
+		if (GET_PTR_TYPE(tree->a[i]) != PTR_TYPE_NULL) {
+			if (p) /* more than one entry */
+				return -2;
+			p = tree->a[i];
+		}
+	}
+
+	if (p && (GET_PTR_TYPE(p) != PTR_TYPE_NOTE))
+		return -2;
+	/* replace tree with p in parent[index] */
+	parent->a[index] = p;
+	free(tree);
+	return 0;
+}
+
+/*
+ * To remove a leaf_node:
+ * Search to the tree location appropriate for the given leaf_node's key:
+ * - If location does not hold a matching entry, abort and do nothing.
+ * - Copy the matching entry's value into the given entry.
+ * - Replace the matching leaf_node with a NULL entry (and free the leaf_node).
+ * - Consolidate int_nodes repeatedly, while walking up the tree towards root.
+ */
+static void note_tree_remove(struct notes_tree *t,
+		struct int_node *tree, unsigned char n,
+		struct leaf_node *entry)
+{
+	struct leaf_node *l;
+	struct int_node *parent_stack[GIT_MAX_RAWSZ];
+	unsigned char i, j;
+	void **p = note_tree_search(t, &tree, &n, entry->key_oid.hash);
+
+	assert(GET_PTR_TYPE(entry) == 0); /* no type bits set */
+	if (GET_PTR_TYPE(*p) != PTR_TYPE_NOTE)
+		return; /* type mismatch, nothing to remove */
+	l = (struct leaf_node *) CLR_PTR_TYPE(*p);
+	if (!oideq(&l->key_oid, &entry->key_oid))
+		return; /* key mismatch, nothing to remove */
+
+	/* we have found a matching entry */
+	oidcpy(&entry->val_oid, &l->val_oid);
+	free(l);
+	*p = SET_PTR_TYPE(NULL, PTR_TYPE_NULL);
+
+	/* consolidate this tree level, and parent levels, if possible */
+	if (!n)
+		return; /* cannot consolidate top level */
+	/* first, build stack of ancestors between root and current node */
+	parent_stack[0] = t->root;
+	for (i = 0; i < n; i++) {
+		j = GET_NIBBLE(i, entry->key_oid.hash);
+		parent_stack[i + 1] = CLR_PTR_TYPE(parent_stack[i]->a[j]);
+	}
+	assert(i == n && parent_stack[i] == tree);
+	/* next, unwind stack until note_tree_consolidate() is done */
+	while (i > 0 &&
+	       !note_tree_consolidate(parent_stack[i], parent_stack[i - 1],
+				      GET_NIBBLE(i - 1, entry->key_oid.hash)))
+		i--;
+}
+
+/*
+ * To insert a leaf_node:
+ * Search to the tree location appropriate for the given leaf_node's key:
+ * - If location is unused (NULL), store the tweaked pointer directly there
+ * - If location holds a note entry that matches the note-to-be-inserted, then
+ *   combine the two notes (by calling the given combine_notes function).
+ * - If location holds a note entry that matches the subtree-to-be-inserted,
+ *   then unpack the subtree-to-be-inserted into the location.
+ * - If location holds a matching subtree entry, unpack the subtree at that
+ *   location, and restart the insert operation from that level.
+ * - Else, create a new int_node, holding both the node-at-location and the
+ *   node-to-be-inserted, and store the new int_node into the location.
+ */
+static int note_tree_insert(struct notes_tree *t, struct int_node *tree,
+		unsigned char n, struct leaf_node *entry, unsigned char type,
+		combine_notes_fn combine_notes)
+{
+	struct int_node *new_node;
+	struct leaf_node *l;
+	void **p = note_tree_search(t, &tree, &n, entry->key_oid.hash);
+	int ret = 0;
+
+	assert(GET_PTR_TYPE(entry) == 0); /* no type bits set */
+	l = (struct leaf_node *) CLR_PTR_TYPE(*p);
+	switch (GET_PTR_TYPE(*p)) {
+	case PTR_TYPE_NULL:
+		assert(!*p);
+		if (is_null_oid(&entry->val_oid))
+			free(entry);
+		else
+			*p = SET_PTR_TYPE(entry, type);
+		return 0;
+	case PTR_TYPE_NOTE:
+		switch (type) {
+		case PTR_TYPE_NOTE:
+			if (oideq(&l->key_oid, &entry->key_oid)) {
+				/* skip concatenation if l == entry */
+				if (oideq(&l->val_oid, &entry->val_oid))
+					return 0;
+
+				ret = combine_notes(&l->val_oid,
+						    &entry->val_oid);
+				if (!ret && is_null_oid(&l->val_oid))
+					note_tree_remove(t, tree, n, entry);
+				free(entry);
+				return ret;
+			}
+			break;
+		case PTR_TYPE_SUBTREE:
+			if (!SUBTREE_SHA1_PREFIXCMP(l->key_oid.hash,
+						    entry->key_oid.hash)) {
+				/* unpack 'entry' */
+				load_subtree(t, entry, tree, n);
+				free(entry);
+				return 0;
+			}
+			break;
+		}
+		break;
+	case PTR_TYPE_SUBTREE:
+		if (!SUBTREE_SHA1_PREFIXCMP(entry->key_oid.hash, l->key_oid.hash)) {
+			/* unpack 'l' and restart insert */
+			*p = NULL;
+			load_subtree(t, l, tree, n);
+			free(l);
+			return note_tree_insert(t, tree, n, entry, type,
+						combine_notes);
+		}
+		break;
+	}
+
+	/* non-matching leaf_node */
+	assert(GET_PTR_TYPE(*p) == PTR_TYPE_NOTE ||
+	       GET_PTR_TYPE(*p) == PTR_TYPE_SUBTREE);
+	if (is_null_oid(&entry->val_oid)) { /* skip insertion of empty note */
+		free(entry);
+		return 0;
+	}
+	new_node = (struct int_node *) xcalloc(1, sizeof(struct int_node));
+	ret = note_tree_insert(t, new_node, n + 1, l, GET_PTR_TYPE(*p),
+			       combine_notes);
+	if (ret)
+		return ret;
+	*p = SET_PTR_TYPE(new_node, PTR_TYPE_INTERNAL);
+	return note_tree_insert(t, new_node, n + 1, entry, type, combine_notes);
+}
+
+/* Free the entire notes data contained in the given tree */
+static void note_tree_free(struct int_node *tree)
+{
+	unsigned int i;
+	for (i = 0; i < 16; i++) {
+		void *p = tree->a[i];
+		switch (GET_PTR_TYPE(p)) {
+		case PTR_TYPE_INTERNAL:
+			note_tree_free(CLR_PTR_TYPE(p));
+			/* fall through */
+		case PTR_TYPE_NOTE:
+		case PTR_TYPE_SUBTREE:
+			free(CLR_PTR_TYPE(p));
+		}
+	}
+}
+
+static int non_note_cmp(const struct non_note *a, const struct non_note *b)
+{
+	return strcmp(a->path, b->path);
+}
+
+/* note: takes ownership of path string */
+static void add_non_note(struct notes_tree *t, char *path,
+		unsigned int mode, const unsigned char *sha1)
+{
+	struct non_note *p = t->prev_non_note, *n;
+	n = (struct non_note *) xmalloc(sizeof(struct non_note));
+	n->next = NULL;
+	n->path = path;
+	n->mode = mode;
+	hashcpy(n->oid.hash, sha1);
+	t->prev_non_note = n;
+
+	if (!t->first_non_note) {
+		t->first_non_note = n;
+		return;
+	}
+
+	if (non_note_cmp(p, n) < 0)
+		; /* do nothing  */
+	else if (non_note_cmp(t->first_non_note, n) <= 0)
+		p = t->first_non_note;
+	else {
+		/* n sorts before t->first_non_note */
+		n->next = t->first_non_note;
+		t->first_non_note = n;
+		return;
+	}
+
+	/* n sorts equal or after p */
+	while (p->next && non_note_cmp(p->next, n) <= 0)
+		p = p->next;
+
+	if (non_note_cmp(p, n) == 0) { /* n ~= p; overwrite p with n */
+		assert(strcmp(p->path, n->path) == 0);
+		p->mode = n->mode;
+		oidcpy(&p->oid, &n->oid);
+		free(n);
+		t->prev_non_note = p;
+		return;
+	}
+
+	/* n sorts between p and p->next */
+	n->next = p->next;
+	p->next = n;
+}
+
+static void load_subtree(struct notes_tree *t, struct leaf_node *subtree,
+		struct int_node *node, unsigned int n)
+{
+	struct object_id object_oid;
+	size_t prefix_len;
+	void *buf;
+	struct tree_desc desc;
+	struct name_entry entry;
+	const unsigned hashsz = the_hash_algo->rawsz;
+
+	buf = fill_tree_descriptor(the_repository, &desc, &subtree->val_oid);
+	if (!buf)
+		die("Could not read %s for notes-index",
+		     oid_to_hex(&subtree->val_oid));
+
+	prefix_len = subtree->key_oid.hash[KEY_INDEX];
+	if (prefix_len >= hashsz)
+		BUG("prefix_len (%"PRIuMAX") is out of range", (uintmax_t)prefix_len);
+	if (prefix_len * 2 < n)
+		BUG("prefix_len (%"PRIuMAX") is too small", (uintmax_t)prefix_len);
+	memcpy(object_oid.hash, subtree->key_oid.hash, prefix_len);
+	while (tree_entry(&desc, &entry)) {
+		unsigned char type;
+		struct leaf_node *l;
+		size_t path_len = strlen(entry.path);
+
+		if (path_len == 2 * (hashsz - prefix_len)) {
+			/* This is potentially the remainder of the SHA-1 */
+
+			if (!S_ISREG(entry.mode))
+				/* notes must be blobs */
+				goto handle_non_note;
+
+			if (hex_to_bytes(object_oid.hash + prefix_len, entry.path,
+					 hashsz - prefix_len))
+				goto handle_non_note; /* entry.path is not a SHA1 */
+
+			type = PTR_TYPE_NOTE;
+		} else if (path_len == 2) {
+			/* This is potentially an internal node */
+			size_t len = prefix_len;
+
+			if (!S_ISDIR(entry.mode))
+				/* internal nodes must be trees */
+				goto handle_non_note;
+
+			if (hex_to_bytes(object_oid.hash + len++, entry.path, 1))
+				goto handle_non_note; /* entry.path is not a SHA1 */
+
+			/*
+			 * Pad the rest of the SHA-1 with zeros,
+			 * except for the last byte, where we write
+			 * the length:
+			 */
+			memset(object_oid.hash + len, 0, hashsz - len - 1);
+			object_oid.hash[KEY_INDEX] = (unsigned char)len;
+
+			type = PTR_TYPE_SUBTREE;
+		} else {
+			/* This can't be part of a note */
+			goto handle_non_note;
+		}
+
+		l = xcalloc(1, sizeof(*l));
+		oidcpy(&l->key_oid, &object_oid);
+		oidcpy(&l->val_oid, &entry.oid);
+		if (note_tree_insert(t, node, n, l, type,
+				     combine_notes_concatenate))
+			die("Failed to load %s %s into notes tree "
+			    "from %s",
+			    type == PTR_TYPE_NOTE ? "note" : "subtree",
+			    oid_to_hex(&l->key_oid), t->ref);
+
+		continue;
+
+handle_non_note:
+		/*
+		 * Determine full path for this non-note entry. The
+		 * filename is already found in entry.path, but the
+		 * directory part of the path must be deduced from the
+		 * subtree containing this entry based on our
+		 * knowledge that the overall notes tree follows a
+		 * strict byte-based progressive fanout structure
+		 * (i.e. using 2/38, 2/2/36, etc. fanouts).
+		 */
+		{
+			struct strbuf non_note_path = STRBUF_INIT;
+			const char *q = oid_to_hex(&subtree->key_oid);
+			size_t i;
+			for (i = 0; i < prefix_len; i++) {
+				strbuf_addch(&non_note_path, *q++);
+				strbuf_addch(&non_note_path, *q++);
+				strbuf_addch(&non_note_path, '/');
+			}
+			strbuf_addstr(&non_note_path, entry.path);
+			add_non_note(t, strbuf_detach(&non_note_path, NULL),
+				     entry.mode, entry.oid.hash);
+		}
+	}
+	free(buf);
+}
+
+/*
+ * Determine optimal on-disk fanout for this part of the notes tree
+ *
+ * Given a (sub)tree and the level in the internal tree structure, determine
+ * whether or not the given existing fanout should be expanded for this
+ * (sub)tree.
+ *
+ * Values of the 'fanout' variable:
+ * - 0: No fanout (all notes are stored directly in the root notes tree)
+ * - 1: 2/38 fanout
+ * - 2: 2/2/36 fanout
+ * - 3: 2/2/2/34 fanout
+ * etc.
+ */
+static unsigned char determine_fanout(struct int_node *tree, unsigned char n,
+		unsigned char fanout)
+{
+	/*
+	 * The following is a simple heuristic that works well in practice:
+	 * For each even-numbered 16-tree level (remember that each on-disk
+	 * fanout level corresponds to _two_ 16-tree levels), peek at all 16
+	 * entries at that tree level. If all of them are either int_nodes or
+	 * subtree entries, then there are likely plenty of notes below this
+	 * level, so we return an incremented fanout.
+	 */
+	unsigned int i;
+	if ((n % 2) || (n > 2 * fanout))
+		return fanout;
+	for (i = 0; i < 16; i++) {
+		switch (GET_PTR_TYPE(tree->a[i])) {
+		case PTR_TYPE_SUBTREE:
+		case PTR_TYPE_INTERNAL:
+			continue;
+		default:
+			return fanout;
+		}
+	}
+	return fanout + 1;
+}
+
+/* hex oid + '/' between each pair of hex digits + NUL */
+#define FANOUT_PATH_MAX GIT_MAX_HEXSZ + FANOUT_PATH_SEPARATORS_MAX + 1
+
+static void construct_path_with_fanout(const unsigned char *hash,
+		unsigned char fanout, char *path)
+{
+	unsigned int i = 0, j = 0;
+	const char *hex_hash = hash_to_hex(hash);
+	assert(fanout < the_hash_algo->rawsz);
+	while (fanout) {
+		path[i++] = hex_hash[j++];
+		path[i++] = hex_hash[j++];
+		path[i++] = '/';
+		fanout--;
+	}
+	xsnprintf(path + i, FANOUT_PATH_MAX - i, "%s", hex_hash + j);
+}
+
+static int for_each_note_helper(struct notes_tree *t, struct int_node *tree,
+		unsigned char n, unsigned char fanout, int flags,
+		each_note_fn fn, void *cb_data)
+{
+	unsigned int i;
+	void *p;
+	int ret = 0;
+	struct leaf_node *l;
+	static char path[FANOUT_PATH_MAX];
+
+	fanout = determine_fanout(tree, n, fanout);
+	for (i = 0; i < 16; i++) {
+redo:
+		p = tree->a[i];
+		switch (GET_PTR_TYPE(p)) {
+		case PTR_TYPE_INTERNAL:
+			/* recurse into int_node */
+			ret = for_each_note_helper(t, CLR_PTR_TYPE(p), n + 1,
+				fanout, flags, fn, cb_data);
+			break;
+		case PTR_TYPE_SUBTREE:
+			l = (struct leaf_node *) CLR_PTR_TYPE(p);
+			/*
+			 * Subtree entries in the note tree represent parts of
+			 * the note tree that have not yet been explored. There
+			 * is a direct relationship between subtree entries at
+			 * level 'n' in the tree, and the 'fanout' variable:
+			 * Subtree entries at level 'n <= 2 * fanout' should be
+			 * preserved, since they correspond exactly to a fanout
+			 * directory in the on-disk structure. However, subtree
+			 * entries at level 'n > 2 * fanout' should NOT be
+			 * preserved, but rather consolidated into the above
+			 * notes tree level. We achieve this by unconditionally
+			 * unpacking subtree entries that exist below the
+			 * threshold level at 'n = 2 * fanout'.
+			 */
+			if (n <= 2 * fanout &&
+			    flags & FOR_EACH_NOTE_YIELD_SUBTREES) {
+				/* invoke callback with subtree */
+				unsigned int path_len =
+					l->key_oid.hash[KEY_INDEX] * 2 + fanout;
+				assert(path_len < FANOUT_PATH_MAX - 1);
+				construct_path_with_fanout(l->key_oid.hash,
+							   fanout,
+							   path);
+				/* Create trailing slash, if needed */
+				if (path[path_len - 1] != '/')
+					path[path_len++] = '/';
+				path[path_len] = '\0';
+				ret = fn(&l->key_oid, &l->val_oid,
+					 path,
+					 cb_data);
+			}
+			if (n > fanout * 2 ||
+			    !(flags & FOR_EACH_NOTE_DONT_UNPACK_SUBTREES)) {
+				/* unpack subtree and resume traversal */
+				tree->a[i] = NULL;
+				load_subtree(t, l, tree, n);
+				free(l);
+				goto redo;
+			}
+			break;
+		case PTR_TYPE_NOTE:
+			l = (struct leaf_node *) CLR_PTR_TYPE(p);
+			construct_path_with_fanout(l->key_oid.hash, fanout,
+						   path);
+			ret = fn(&l->key_oid, &l->val_oid, path,
+				 cb_data);
+			break;
+		}
+		if (ret)
+			return ret;
+	}
+	return 0;
+}
+
+struct tree_write_stack {
+	struct tree_write_stack *next;
+	struct strbuf buf;
+	char path[2]; /* path to subtree in next, if any */
+};
+
+static inline int matches_tree_write_stack(struct tree_write_stack *tws,
+		const char *full_path)
+{
+	return  full_path[0] == tws->path[0] &&
+		full_path[1] == tws->path[1] &&
+		full_path[2] == '/';
+}
+
+static void write_tree_entry(struct strbuf *buf, unsigned int mode,
+		const char *path, unsigned int path_len, const
+		unsigned char *hash)
+{
+	strbuf_addf(buf, "%o %.*s%c", mode, path_len, path, '\0');
+	strbuf_add(buf, hash, the_hash_algo->rawsz);
+}
+
+static void tree_write_stack_init_subtree(struct tree_write_stack *tws,
+		const char *path)
+{
+	struct tree_write_stack *n;
+	assert(!tws->next);
+	assert(tws->path[0] == '\0' && tws->path[1] == '\0');
+	n = (struct tree_write_stack *)
+		xmalloc(sizeof(struct tree_write_stack));
+	n->next = NULL;
+	strbuf_init(&n->buf, 256 * (32 + the_hash_algo->hexsz)); /* assume 256 entries per tree */
+	n->path[0] = n->path[1] = '\0';
+	tws->next = n;
+	tws->path[0] = path[0];
+	tws->path[1] = path[1];
+}
+
+static int tree_write_stack_finish_subtree(struct tree_write_stack *tws)
+{
+	int ret;
+	struct tree_write_stack *n = tws->next;
+	struct object_id s;
+	if (n) {
+		ret = tree_write_stack_finish_subtree(n);
+		if (ret)
+			return ret;
+		ret = write_object_file(n->buf.buf, n->buf.len, tree_type, &s);
+		if (ret)
+			return ret;
+		strbuf_release(&n->buf);
+		free(n);
+		tws->next = NULL;
+		write_tree_entry(&tws->buf, 040000, tws->path, 2, s.hash);
+		tws->path[0] = tws->path[1] = '\0';
+	}
+	return 0;
+}
+
+static int write_each_note_helper(struct tree_write_stack *tws,
+		const char *path, unsigned int mode,
+		const struct object_id *oid)
+{
+	size_t path_len = strlen(path);
+	unsigned int n = 0;
+	int ret;
+
+	/* Determine common part of tree write stack */
+	while (tws && 3 * n < path_len &&
+	       matches_tree_write_stack(tws, path + 3 * n)) {
+		n++;
+		tws = tws->next;
+	}
+
+	/* tws point to last matching tree_write_stack entry */
+	ret = tree_write_stack_finish_subtree(tws);
+	if (ret)
+		return ret;
+
+	/* Start subtrees needed to satisfy path */
+	while (3 * n + 2 < path_len && path[3 * n + 2] == '/') {
+		tree_write_stack_init_subtree(tws, path + 3 * n);
+		n++;
+		tws = tws->next;
+	}
+
+	/* There should be no more directory components in the given path */
+	assert(memchr(path + 3 * n, '/', path_len - (3 * n)) == NULL);
+
+	/* Finally add given entry to the current tree object */
+	write_tree_entry(&tws->buf, mode, path + 3 * n, path_len - (3 * n),
+			 oid->hash);
+
+	return 0;
+}
+
+struct write_each_note_data {
+	struct tree_write_stack *root;
+	struct non_note *next_non_note;
+};
+
+static int write_each_non_note_until(const char *note_path,
+		struct write_each_note_data *d)
+{
+	struct non_note *n = d->next_non_note;
+	int cmp = 0, ret;
+	while (n && (!note_path || (cmp = strcmp(n->path, note_path)) <= 0)) {
+		if (note_path && cmp == 0)
+			; /* do nothing, prefer note to non-note */
+		else {
+			ret = write_each_note_helper(d->root, n->path, n->mode,
+						     &n->oid);
+			if (ret)
+				return ret;
+		}
+		n = n->next;
+	}
+	d->next_non_note = n;
+	return 0;
+}
+
+static int write_each_note(const struct object_id *object_oid,
+		const struct object_id *note_oid, char *note_path,
+		void *cb_data)
+{
+	struct write_each_note_data *d =
+		(struct write_each_note_data *) cb_data;
+	size_t note_path_len = strlen(note_path);
+	unsigned int mode = 0100644;
+
+	if (note_path[note_path_len - 1] == '/') {
+		/* subtree entry */
+		note_path_len--;
+		note_path[note_path_len] = '\0';
+		mode = 040000;
+	}
+	assert(note_path_len <= GIT_MAX_HEXSZ + FANOUT_PATH_SEPARATORS);
+
+	/* Weave non-note entries into note entries */
+	return  write_each_non_note_until(note_path, d) ||
+		write_each_note_helper(d->root, note_path, mode, note_oid);
+}
+
+struct note_delete_list {
+	struct note_delete_list *next;
+	const unsigned char *sha1;
+};
+
+static int prune_notes_helper(const struct object_id *object_oid,
+		const struct object_id *note_oid, char *note_path,
+		void *cb_data)
+{
+	struct note_delete_list **l = (struct note_delete_list **) cb_data;
+	struct note_delete_list *n;
+
+	if (has_object_file(object_oid))
+		return 0; /* nothing to do for this note */
+
+	/* failed to find object => prune this note */
+	n = (struct note_delete_list *) xmalloc(sizeof(*n));
+	n->next = *l;
+	n->sha1 = object_oid->hash;
+	*l = n;
+	return 0;
+}
+
+int combine_notes_concatenate(struct object_id *cur_oid,
+			      const struct object_id *new_oid)
+{
+	char *cur_msg = NULL, *new_msg = NULL, *buf;
+	unsigned long cur_len, new_len, buf_len;
+	enum object_type cur_type, new_type;
+	int ret;
+
+	/* read in both note blob objects */
+	if (!is_null_oid(new_oid))
+		new_msg = read_object_file(new_oid, &new_type, &new_len);
+	if (!new_msg || !new_len || new_type != OBJ_BLOB) {
+		free(new_msg);
+		return 0;
+	}
+	if (!is_null_oid(cur_oid))
+		cur_msg = read_object_file(cur_oid, &cur_type, &cur_len);
+	if (!cur_msg || !cur_len || cur_type != OBJ_BLOB) {
+		free(cur_msg);
+		free(new_msg);
+		oidcpy(cur_oid, new_oid);
+		return 0;
+	}
+
+	/* we will separate the notes by two newlines anyway */
+	if (cur_msg[cur_len - 1] == '\n')
+		cur_len--;
+
+	/* concatenate cur_msg and new_msg into buf */
+	buf_len = cur_len + 2 + new_len;
+	buf = (char *) xmalloc(buf_len);
+	memcpy(buf, cur_msg, cur_len);
+	buf[cur_len] = '\n';
+	buf[cur_len + 1] = '\n';
+	memcpy(buf + cur_len + 2, new_msg, new_len);
+	free(cur_msg);
+	free(new_msg);
+
+	/* create a new blob object from buf */
+	ret = write_object_file(buf, buf_len, blob_type, cur_oid);
+	free(buf);
+	return ret;
+}
+
+int combine_notes_overwrite(struct object_id *cur_oid,
+			    const struct object_id *new_oid)
+{
+	oidcpy(cur_oid, new_oid);
+	return 0;
+}
+
+int combine_notes_ignore(struct object_id *cur_oid,
+			 const struct object_id *new_oid)
+{
+	return 0;
+}
+
+/*
+ * Add the lines from the named object to list, with trailing
+ * newlines removed.
+ */
+static int string_list_add_note_lines(struct string_list *list,
+				      const struct object_id *oid)
+{
+	char *data;
+	unsigned long len;
+	enum object_type t;
+
+	if (is_null_oid(oid))
+		return 0;
+
+	/* read_sha1_file NUL-terminates */
+	data = read_object_file(oid, &t, &len);
+	if (t != OBJ_BLOB || !data || !len) {
+		free(data);
+		return t != OBJ_BLOB || !data;
+	}
+
+	/*
+	 * If the last line of the file is EOL-terminated, this will
+	 * add an empty string to the list.  But it will be removed
+	 * later, along with any empty strings that came from empty
+	 * lines within the file.
+	 */
+	string_list_split(list, data, '\n', -1);
+	free(data);
+	return 0;
+}
+
+static int string_list_join_lines_helper(struct string_list_item *item,
+					 void *cb_data)
+{
+	struct strbuf *buf = cb_data;
+	strbuf_addstr(buf, item->string);
+	strbuf_addch(buf, '\n');
+	return 0;
+}
+
+int combine_notes_cat_sort_uniq(struct object_id *cur_oid,
+				const struct object_id *new_oid)
+{
+	struct string_list sort_uniq_list = STRING_LIST_INIT_DUP;
+	struct strbuf buf = STRBUF_INIT;
+	int ret = 1;
+
+	/* read both note blob objects into unique_lines */
+	if (string_list_add_note_lines(&sort_uniq_list, cur_oid))
+		goto out;
+	if (string_list_add_note_lines(&sort_uniq_list, new_oid))
+		goto out;
+	string_list_remove_empty_items(&sort_uniq_list, 0);
+	string_list_sort(&sort_uniq_list);
+	string_list_remove_duplicates(&sort_uniq_list, 0);
+
+	/* create a new blob object from sort_uniq_list */
+	if (for_each_string_list(&sort_uniq_list,
+				 string_list_join_lines_helper, &buf))
+		goto out;
+
+	ret = write_object_file(buf.buf, buf.len, blob_type, cur_oid);
+
+out:
+	strbuf_release(&buf);
+	string_list_clear(&sort_uniq_list, 0);
+	return ret;
+}
+
+static int string_list_add_one_ref(const char *refname, const struct object_id *oid,
+				   int flag, void *cb)
+{
+	struct string_list *refs = cb;
+	if (!unsorted_string_list_has_string(refs, refname))
+		string_list_append(refs, refname);
+	return 0;
+}
+
+/*
+ * The list argument must have strdup_strings set on it.
+ */
+void string_list_add_refs_by_glob(struct string_list *list, const char *glob)
+{
+	assert(list->strdup_strings);
+	if (has_glob_specials(glob)) {
+		for_each_glob_ref(string_list_add_one_ref, glob, list);
+	} else {
+		struct object_id oid;
+		if (get_oid(glob, &oid))
+			warning("notes ref %s is invalid", glob);
+		if (!unsorted_string_list_has_string(list, glob))
+			string_list_append(list, glob);
+	}
+}
+
+void string_list_add_refs_from_colon_sep(struct string_list *list,
+					 const char *globs)
+{
+	struct string_list split = STRING_LIST_INIT_NODUP;
+	char *globs_copy = xstrdup(globs);
+	int i;
+
+	string_list_split_in_place(&split, globs_copy, ':', -1);
+	string_list_remove_empty_items(&split, 0);
+
+	for (i = 0; i < split.nr; i++)
+		string_list_add_refs_by_glob(list, split.items[i].string);
+
+	string_list_clear(&split, 0);
+	free(globs_copy);
+}
+
+static int notes_display_config(const char *k, const char *v, void *cb)
+{
+	int *load_refs = cb;
+
+	if (*load_refs && !strcmp(k, "notes.displayref")) {
+		if (!v)
+			config_error_nonbool(k);
+		string_list_add_refs_by_glob(&display_notes_refs, v);
+	}
+
+	return 0;
+}
+
+const char *default_notes_ref(void)
+{
+	const char *notes_ref = NULL;
+	if (!notes_ref)
+		notes_ref = getenv(GIT_NOTES_REF_ENVIRONMENT);
+	if (!notes_ref)
+		notes_ref = notes_ref_name; /* value of core.notesRef config */
+	if (!notes_ref)
+		notes_ref = GIT_NOTES_DEFAULT_REF;
+	return notes_ref;
+}
+
+void init_notes(struct notes_tree *t, const char *notes_ref,
+		combine_notes_fn combine_notes, int flags)
+{
+	struct object_id oid, object_oid;
+	unsigned short mode;
+	struct leaf_node root_tree;
+
+	if (!t)
+		t = &default_notes_tree;
+	assert(!t->initialized);
+
+	if (!notes_ref)
+		notes_ref = default_notes_ref();
+
+	if (!combine_notes)
+		combine_notes = combine_notes_concatenate;
+
+	t->root = (struct int_node *) xcalloc(1, sizeof(struct int_node));
+	t->first_non_note = NULL;
+	t->prev_non_note = NULL;
+	t->ref = xstrdup_or_null(notes_ref);
+	t->update_ref = (flags & NOTES_INIT_WRITABLE) ? t->ref : NULL;
+	t->combine_notes = combine_notes;
+	t->initialized = 1;
+	t->dirty = 0;
+
+	if (flags & NOTES_INIT_EMPTY || !notes_ref ||
+	    get_oid_treeish(notes_ref, &object_oid))
+		return;
+	if (flags & NOTES_INIT_WRITABLE && read_ref(notes_ref, &object_oid))
+		die("Cannot use notes ref %s", notes_ref);
+	if (get_tree_entry(the_repository, &object_oid, "", &oid, &mode))
+		die("Failed to read notes tree referenced by %s (%s)",
+		    notes_ref, oid_to_hex(&object_oid));
+
+	oidclr(&root_tree.key_oid);
+	oidcpy(&root_tree.val_oid, &oid);
+	load_subtree(t, &root_tree, t->root, 0);
+}
+
+struct notes_tree **load_notes_trees(struct string_list *refs, int flags)
+{
+	struct string_list_item *item;
+	int counter = 0;
+	struct notes_tree **trees;
+	ALLOC_ARRAY(trees, refs->nr + 1);
+	for_each_string_list_item(item, refs) {
+		struct notes_tree *t = xcalloc(1, sizeof(struct notes_tree));
+		init_notes(t, item->string, combine_notes_ignore, flags);
+		trees[counter++] = t;
+	}
+	trees[counter] = NULL;
+	return trees;
+}
+
+void init_display_notes(struct display_notes_opt *opt)
+{
+	char *display_ref_env;
+	int load_config_refs = 0;
+	display_notes_refs.strdup_strings = 1;
+
+	assert(!display_notes_trees);
+
+	if (!opt || opt->use_default_notes > 0 ||
+	    (opt->use_default_notes == -1 && !opt->extra_notes_refs.nr)) {
+		string_list_append(&display_notes_refs, default_notes_ref());
+		display_ref_env = getenv(GIT_NOTES_DISPLAY_REF_ENVIRONMENT);
+		if (display_ref_env) {
+			string_list_add_refs_from_colon_sep(&display_notes_refs,
+							    display_ref_env);
+			load_config_refs = 0;
+		} else
+			load_config_refs = 1;
+	}
+
+	git_config(notes_display_config, &load_config_refs);
+
+	if (opt) {
+		struct string_list_item *item;
+		for_each_string_list_item(item, &opt->extra_notes_refs)
+			string_list_add_refs_by_glob(&display_notes_refs,
+						     item->string);
+	}
+
+	display_notes_trees = load_notes_trees(&display_notes_refs, 0);
+	string_list_clear(&display_notes_refs, 0);
+}
+
+int add_note(struct notes_tree *t, const struct object_id *object_oid,
+		const struct object_id *note_oid, combine_notes_fn combine_notes)
+{
+	struct leaf_node *l;
+
+	if (!t)
+		t = &default_notes_tree;
+	assert(t->initialized);
+	t->dirty = 1;
+	if (!combine_notes)
+		combine_notes = t->combine_notes;
+	l = (struct leaf_node *) xmalloc(sizeof(struct leaf_node));
+	oidcpy(&l->key_oid, object_oid);
+	oidcpy(&l->val_oid, note_oid);
+	return note_tree_insert(t, t->root, 0, l, PTR_TYPE_NOTE, combine_notes);
+}
+
+int remove_note(struct notes_tree *t, const unsigned char *object_sha1)
+{
+	struct leaf_node l;
+
+	if (!t)
+		t = &default_notes_tree;
+	assert(t->initialized);
+	hashcpy(l.key_oid.hash, object_sha1);
+	oidclr(&l.val_oid);
+	note_tree_remove(t, t->root, 0, &l);
+	if (is_null_oid(&l.val_oid)) /* no note was removed */
+		return 1;
+	t->dirty = 1;
+	return 0;
+}
+
+const struct object_id *get_note(struct notes_tree *t,
+		const struct object_id *oid)
+{
+	struct leaf_node *found;
+
+	if (!t)
+		t = &default_notes_tree;
+	assert(t->initialized);
+	found = note_tree_find(t, t->root, 0, oid->hash);
+	return found ? &found->val_oid : NULL;
+}
+
+int for_each_note(struct notes_tree *t, int flags, each_note_fn fn,
+		void *cb_data)
+{
+	if (!t)
+		t = &default_notes_tree;
+	assert(t->initialized);
+	return for_each_note_helper(t, t->root, 0, 0, flags, fn, cb_data);
+}
+
+int write_notes_tree(struct notes_tree *t, struct object_id *result)
+{
+	struct tree_write_stack root;
+	struct write_each_note_data cb_data;
+	int ret;
+	int flags;
+
+	if (!t)
+		t = &default_notes_tree;
+	assert(t->initialized);
+
+	/* Prepare for traversal of current notes tree */
+	root.next = NULL; /* last forward entry in list is grounded */
+	strbuf_init(&root.buf, 256 * (32 + the_hash_algo->hexsz)); /* assume 256 entries */
+	root.path[0] = root.path[1] = '\0';
+	cb_data.root = &root;
+	cb_data.next_non_note = t->first_non_note;
+
+	/* Write tree objects representing current notes tree */
+	flags = FOR_EACH_NOTE_DONT_UNPACK_SUBTREES |
+		FOR_EACH_NOTE_YIELD_SUBTREES;
+	ret = for_each_note(t, flags, write_each_note, &cb_data) ||
+	      write_each_non_note_until(NULL, &cb_data) ||
+	      tree_write_stack_finish_subtree(&root) ||
+	      write_object_file(root.buf.buf, root.buf.len, tree_type, result);
+	strbuf_release(&root.buf);
+	return ret;
+}
+
+void prune_notes(struct notes_tree *t, int flags)
+{
+	struct note_delete_list *l = NULL;
+
+	if (!t)
+		t = &default_notes_tree;
+	assert(t->initialized);
+
+	for_each_note(t, 0, prune_notes_helper, &l);
+
+	while (l) {
+		if (flags & NOTES_PRUNE_VERBOSE)
+			printf("%s\n", hash_to_hex(l->sha1));
+		if (!(flags & NOTES_PRUNE_DRYRUN))
+			remove_note(t, l->sha1);
+		l = l->next;
+	}
+}
+
+void free_notes(struct notes_tree *t)
+{
+	if (!t)
+		t = &default_notes_tree;
+	if (t->root)
+		note_tree_free(t->root);
+	free(t->root);
+	while (t->first_non_note) {
+		t->prev_non_note = t->first_non_note->next;
+		free(t->first_non_note->path);
+		free(t->first_non_note);
+		t->first_non_note = t->prev_non_note;
+	}
+	free(t->ref);
+	memset(t, 0, sizeof(struct notes_tree));
+}
+
+/*
+ * Fill the given strbuf with the notes associated with the given object.
+ *
+ * If the given notes_tree structure is not initialized, it will be auto-
+ * initialized to the default value (see documentation for init_notes() above).
+ * If the given notes_tree is NULL, the internal/default notes_tree will be
+ * used instead.
+ *
+ * (raw != 0) gives the %N userformat; otherwise, the note message is given
+ * for human consumption.
+ */
+static void format_note(struct notes_tree *t, const struct object_id *object_oid,
+			struct strbuf *sb, const char *output_encoding, int raw)
+{
+	static const char utf8[] = "utf-8";
+	const struct object_id *oid;
+	char *msg, *msg_p;
+	unsigned long linelen, msglen;
+	enum object_type type;
+
+	if (!t)
+		t = &default_notes_tree;
+	if (!t->initialized)
+		init_notes(t, NULL, NULL, 0);
+
+	oid = get_note(t, object_oid);
+	if (!oid)
+		return;
+
+	if (!(msg = read_object_file(oid, &type, &msglen)) || type != OBJ_BLOB) {
+		free(msg);
+		return;
+	}
+
+	if (output_encoding && *output_encoding &&
+	    !is_encoding_utf8(output_encoding)) {
+		char *reencoded = reencode_string(msg, output_encoding, utf8);
+		if (reencoded) {
+			free(msg);
+			msg = reencoded;
+			msglen = strlen(msg);
+		}
+	}
+
+	/* we will end the annotation by a newline anyway */
+	if (msglen && msg[msglen - 1] == '\n')
+		msglen--;
+
+	if (!raw) {
+		const char *ref = t->ref;
+		if (!ref || !strcmp(ref, GIT_NOTES_DEFAULT_REF)) {
+			strbuf_addstr(sb, "\nNotes:\n");
+		} else {
+			if (starts_with(ref, "refs/"))
+				ref += 5;
+			if (starts_with(ref, "notes/"))
+				ref += 6;
+			strbuf_addf(sb, "\nNotes (%s):\n", ref);
+		}
+	}
+
+	for (msg_p = msg; msg_p < msg + msglen; msg_p += linelen + 1) {
+		linelen = strchrnul(msg_p, '\n') - msg_p;
+
+		if (!raw)
+			strbuf_addstr(sb, "    ");
+		strbuf_add(sb, msg_p, linelen);
+		strbuf_addch(sb, '\n');
+	}
+
+	free(msg);
+}
+
+void format_display_notes(const struct object_id *object_oid,
+			  struct strbuf *sb, const char *output_encoding, int raw)
+{
+	int i;
+	assert(display_notes_trees);
+	for (i = 0; display_notes_trees[i]; i++)
+		format_note(display_notes_trees[i], object_oid, sb,
+			    output_encoding, raw);
+}
+
+int copy_note(struct notes_tree *t,
+	      const struct object_id *from_obj, const struct object_id *to_obj,
+	      int force, combine_notes_fn combine_notes)
+{
+	const struct object_id *note = get_note(t, from_obj);
+	const struct object_id *existing_note = get_note(t, to_obj);
+
+	if (!force && existing_note)
+		return 1;
+
+	if (note)
+		return add_note(t, to_obj, note, combine_notes);
+	else if (existing_note)
+		return add_note(t, to_obj, &null_oid, combine_notes);
+
+	return 0;
+}
+
+void expand_notes_ref(struct strbuf *sb)
+{
+	if (starts_with(sb->buf, "refs/notes/"))
+		return; /* we're happy */
+	else if (starts_with(sb->buf, "notes/"))
+		strbuf_insert(sb, 0, "refs/", 5);
+	else
+		strbuf_insert(sb, 0, "refs/notes/", 11);
+}
+
+void expand_loose_notes_ref(struct strbuf *sb)
+{
+	struct object_id object;
+
+	if (get_oid(sb->buf, &object)) {
+		/* fallback to expand_notes_ref */
+		expand_notes_ref(sb);
+	}
+}