test-lib: unset GIT_NOTES_REF to stop it from influencing tests
[gitweb.git] / notes.c
diff --git a/notes.c b/notes.c
index eabd6f30cd7142b5c95e621a9e784c5f10833f9c..3ba3e6de17a562f309e6d8c64d609768fd740110 100644 (file)
--- a/notes.c
+++ b/notes.c
@@ -1,5 +1,7 @@
 #include "cache.h"
 #include "notes.h"
+#include "blob.h"
+#include "tree.h"
 #include "utf8.h"
 #include "strbuf.h"
 #include "tree-walk.h"
@@ -35,6 +37,21 @@ struct leaf_node {
        unsigned char val_sha1[20];
 };
 
+/*
+ * 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;
+       unsigned char sha1[20];
+};
+
 #define PTR_TYPE_NULL     0
 #define PTR_TYPE_INTERNAL 1
 #define PTR_TYPE_NOTE     2
@@ -49,12 +66,10 @@ struct leaf_node {
 #define SUBTREE_SHA1_PREFIXCMP(key_sha1, subtree_sha1) \
        (memcmp(key_sha1, subtree_sha1, subtree_sha1[19]))
 
-static struct int_node root_node;
-
-static int initialized;
+struct notes_tree default_notes_tree;
 
-static void load_subtree(struct leaf_node *subtree, struct int_node *node,
-               unsigned int n);
+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:
@@ -71,7 +86,7 @@ static void load_subtree(struct leaf_node *subtree, struct int_node *node,
  *      - 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 int_node **tree,
+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;
@@ -83,9 +98,9 @@ static void **note_tree_search(struct int_node **tree,
                if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_sha1)) {
                        /* unpack tree and resume search */
                        (*tree)->a[0] = NULL;
-                       load_subtree(l, *tree, *n);
+                       load_subtree(t, l, *tree, *n);
                        free(l);
-                       return note_tree_search(tree, n, key_sha1);
+                       return note_tree_search(t, tree, n, key_sha1);
                }
        }
 
@@ -95,15 +110,15 @@ static void **note_tree_search(struct int_node **tree,
        case PTR_TYPE_INTERNAL:
                *tree = CLR_PTR_TYPE(p);
                (*n)++;
-               return note_tree_search(tree, n, key_sha1);
+               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_sha1)) {
                        /* unpack tree and resume search */
                        (*tree)->a[i] = NULL;
-                       load_subtree(l, *tree, *n);
+                       load_subtree(t, l, *tree, *n);
                        free(l);
-                       return note_tree_search(tree, n, key_sha1);
+                       return note_tree_search(t, tree, n, key_sha1);
                }
                /* fall through */
        default:
@@ -116,10 +131,11 @@ static void **note_tree_search(struct int_node **tree,
  * 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 int_node *tree, unsigned char n,
+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(&tree, &n, 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 (!hashcmp(key_sha1, l->key_sha1))
@@ -128,55 +144,12 @@ static struct leaf_node *note_tree_find(struct int_node *tree, unsigned char n,
        return NULL;
 }
 
-/* Create a new blob object by concatenating the two given blob objects */
-static int concatenate_notes(unsigned char *cur_sha1,
-               const unsigned char *new_sha1)
-{
-       char *cur_msg, *new_msg, *buf;
-       unsigned long cur_len, new_len, buf_len;
-       enum object_type cur_type, new_type;
-       int ret;
-
-       /* read in both note blob objects */
-       new_msg = read_sha1_file(new_sha1, &new_type, &new_len);
-       if (!new_msg || !new_len || new_type != OBJ_BLOB) {
-               free(new_msg);
-               return 0;
-       }
-       cur_msg = read_sha1_file(cur_sha1, &cur_type, &cur_len);
-       if (!cur_msg || !cur_len || cur_type != OBJ_BLOB) {
-               free(cur_msg);
-               free(new_msg);
-               hashcpy(cur_sha1, new_sha1);
-               return 0;
-       }
-
-       /* we will separate the notes by a newline anyway */
-       if (cur_msg[cur_len - 1] == '\n')
-               cur_len--;
-
-       /* concatenate cur_msg and new_msg into buf */
-       buf_len = cur_len + 1 + new_len;
-       buf = (char *) xmalloc(buf_len);
-       memcpy(buf, cur_msg, cur_len);
-       buf[cur_len] = '\n';
-       memcpy(buf + cur_len + 1, new_msg, new_len);
-
-       free(cur_msg);
-       free(new_msg);
-
-       /* create a new blob object from buf */
-       ret = write_sha1_file(buf, buf_len, "blob", cur_sha1);
-       free(buf);
-       return ret;
-}
-
 /*
  * 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
- *   concatenate the two notes.
+ *   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
@@ -184,12 +157,13 @@ static int concatenate_notes(unsigned char *cur_sha1,
  * - 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 void note_tree_insert(struct int_node *tree, unsigned char n,
-               struct leaf_node *entry, unsigned char type)
+static void 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(&tree, &n, entry->key_sha1);
+       void **p = note_tree_search(t, &tree, &n, entry->key_sha1);
 
        assert(GET_PTR_TYPE(entry) == 0); /* no type bits set */
        l = (struct leaf_node *) CLR_PTR_TYPE(*p);
@@ -206,12 +180,11 @@ static void note_tree_insert(struct int_node *tree, unsigned char n,
                                if (!hashcmp(l->val_sha1, entry->val_sha1))
                                        return;
 
-                               if (concatenate_notes(l->val_sha1,
-                                               entry->val_sha1))
-                                       die("failed to concatenate note %s "
-                                           "into note %s for object %s",
-                                           sha1_to_hex(entry->val_sha1),
+                               if (combine_notes(l->val_sha1, entry->val_sha1))
+                                       die("failed to combine notes %s and %s"
+                                           " for object %s",
                                            sha1_to_hex(l->val_sha1),
+                                           sha1_to_hex(entry->val_sha1),
                                            sha1_to_hex(l->key_sha1));
                                free(entry);
                                return;
@@ -221,7 +194,7 @@ static void note_tree_insert(struct int_node *tree, unsigned char n,
                        if (!SUBTREE_SHA1_PREFIXCMP(l->key_sha1,
                                                    entry->key_sha1)) {
                                /* unpack 'entry' */
-                               load_subtree(entry, tree, n);
+                               load_subtree(t, entry, tree, n);
                                free(entry);
                                return;
                        }
@@ -232,9 +205,10 @@ static void note_tree_insert(struct int_node *tree, unsigned char n,
                if (!SUBTREE_SHA1_PREFIXCMP(entry->key_sha1, l->key_sha1)) {
                        /* unpack 'l' and restart insert */
                        *p = NULL;
-                       load_subtree(l, tree, n);
+                       load_subtree(t, l, tree, n);
                        free(l);
-                       note_tree_insert(tree, n, entry, type);
+                       note_tree_insert(t, tree, n, entry, type,
+                                        combine_notes);
                        return;
                }
                break;
@@ -244,9 +218,10 @@ static void note_tree_insert(struct int_node *tree, unsigned char n,
        assert(GET_PTR_TYPE(*p) == PTR_TYPE_NOTE ||
               GET_PTR_TYPE(*p) == PTR_TYPE_SUBTREE);
        new_node = (struct int_node *) xcalloc(sizeof(struct int_node), 1);
-       note_tree_insert(new_node, n + 1, l, GET_PTR_TYPE(*p));
+       note_tree_insert(t, new_node, n + 1, l, GET_PTR_TYPE(*p),
+                        combine_notes);
        *p = SET_PTR_TYPE(new_node, PTR_TYPE_INTERNAL);
-       note_tree_insert(new_node, n + 1, entry, type);
+       note_tree_insert(t, new_node, n + 1, entry, type, combine_notes);
 }
 
 /*
@@ -286,13 +261,13 @@ static int note_tree_consolidate(struct int_node *tree,
  * - 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 int_node *tree, unsigned char n,
-               struct leaf_node *entry)
+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[20];
        unsigned char i, j;
-       void **p = note_tree_search(&tree, &n, entry->key_sha1);
+       void **p = note_tree_search(t, &tree, &n, entry->key_sha1);
 
        assert(GET_PTR_TYPE(entry) == 0); /* no type bits set */
        if (GET_PTR_TYPE(*p) != PTR_TYPE_NOTE)
@@ -309,7 +284,7 @@ static void note_tree_remove(struct int_node *tree, unsigned char n,
        if (!n)
                return; /* cannot consolidate top level */
        /* first, build stack of ancestors between root and current node */
-       parent_stack[0] = &root_node;
+       parent_stack[0] = t->root;
        for (i = 0; i < n; i++) {
                j = GET_NIBBLE(i, entry->key_sha1);
                parent_stack[i + 1] = CLR_PTR_TYPE(parent_stack[i]->a[j]);
@@ -367,14 +342,67 @@ static int get_sha1_hex_segment(const char *hex, unsigned int hex_len,
        return len;
 }
 
-static void load_subtree(struct leaf_node *subtree, struct int_node *node,
-               unsigned int n)
+static int non_note_cmp(const struct non_note *a, const struct non_note *b)
+{
+       return strcmp(a->path, b->path);
+}
+
+static void add_non_note(struct notes_tree *t, const 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 = xstrdup(path);
+       n->mode = mode;
+       hashcpy(n->sha1, 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;
+               hashcpy(p->sha1, n->sha1);
+               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)
 {
        unsigned char object_sha1[20];
        unsigned int prefix_len;
        void *buf;
        struct tree_desc desc;
        struct name_entry entry;
+       int len, path_len;
+       unsigned char type;
+       struct leaf_node *l;
 
        buf = fill_tree_descriptor(&desc, subtree->val_sha1);
        if (!buf)
@@ -385,29 +413,67 @@ static void load_subtree(struct leaf_node *subtree, struct int_node *node,
        assert(prefix_len * 2 >= n);
        memcpy(object_sha1, subtree->key_sha1, prefix_len);
        while (tree_entry(&desc, &entry)) {
-               int len = get_sha1_hex_segment(entry.path, strlen(entry.path),
+               path_len = strlen(entry.path);
+               len = get_sha1_hex_segment(entry.path, path_len,
                                object_sha1 + prefix_len, 20 - prefix_len);
                if (len < 0)
-                       continue; /* entry.path is not a SHA1 sum. Skip */
+                       goto handle_non_note; /* entry.path is not a SHA1 */
                len += prefix_len;
 
                /*
                 * If object SHA1 is complete (len == 20), assume note object
-                * If object SHA1 is incomplete (len < 20), assume note subtree
+                * If object SHA1 is incomplete (len < 20), and current
+                * component consists of 2 hex chars, assume note subtree
                 */
                if (len <= 20) {
-                       unsigned char type = PTR_TYPE_NOTE;
-                       struct leaf_node *l = (struct leaf_node *)
+                       type = PTR_TYPE_NOTE;
+                       l = (struct leaf_node *)
                                xcalloc(sizeof(struct leaf_node), 1);
                        hashcpy(l->key_sha1, object_sha1);
                        hashcpy(l->val_sha1, entry.sha1);
                        if (len < 20) {
-                               if (!S_ISDIR(entry.mode))
-                                       continue; /* entry cannot be subtree */
+                               if (!S_ISDIR(entry.mode) || path_len != 2)
+                                       goto handle_non_note; /* not subtree */
                                l->key_sha1[19] = (unsigned char) len;
                                type = PTR_TYPE_SUBTREE;
                        }
-                       note_tree_insert(node, n, l, type);
+                       note_tree_insert(t, node, n, l, type,
+                                        combine_notes_concatenate);
+               }
+               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. We assume here that the overall notes
+                * tree follows a strict byte-based progressive fanout
+                * structure (i.e. using 2/38, 2/2/36, etc. fanouts, and not
+                * e.g. 4/36 fanout). This means that if a non-note is found at
+                * path "dead/beef", the following code will register it as
+                * being found on "de/ad/beef".
+                * On the other hand, if you use such non-obvious non-note
+                * paths in the middle of a notes tree, you deserve what's
+                * coming to you ;). Note that for non-notes that are not
+                * SHA1-like at the top level, there will be no problems.
+                *
+                * To conclude, it is strongly advised to make sure non-notes
+                * have at least one non-hex character in the top-level path
+                * component.
+                */
+               {
+                       char non_note_path[PATH_MAX];
+                       char *p = non_note_path;
+                       const char *q = sha1_to_hex(subtree->key_sha1);
+                       int i;
+                       for (i = 0; i < prefix_len; i++) {
+                               *p++ = *q++;
+                               *p++ = *q++;
+                               *p++ = '/';
+                       }
+                       strcpy(p, entry.path);
+                       add_non_note(t, non_note_path, entry.mode, entry.sha1);
                }
        }
        free(buf);
@@ -468,9 +534,9 @@ static void construct_path_with_fanout(const unsigned char *sha1,
        strcpy(path + i, hex_sha1 + j);
 }
 
-static int for_each_note_helper(struct int_node *tree, unsigned char n,
-               unsigned char fanout, int flags, each_note_fn fn,
-               void *cb_data)
+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;
@@ -485,7 +551,7 @@ static int for_each_note_helper(struct int_node *tree, unsigned char n,
                switch (GET_PTR_TYPE(p)) {
                case PTR_TYPE_INTERNAL:
                        /* recurse into int_node */
-                       ret = for_each_note_helper(CLR_PTR_TYPE(p), n + 1,
+                       ret = for_each_note_helper(t, CLR_PTR_TYPE(p), n + 1,
                                fanout, flags, fn, cb_data);
                        break;
                case PTR_TYPE_SUBTREE:
@@ -523,7 +589,7 @@ static int for_each_note_helper(struct int_node *tree, unsigned char n,
                            !(flags & FOR_EACH_NOTE_DONT_UNPACK_SUBTREES)) {
                                /* unpack subtree and resume traversal */
                                tree->a[i] = NULL;
-                               load_subtree(l, tree, n);
+                               load_subtree(t, l, tree, n);
                                free(l);
                                goto redo;
                        }
@@ -540,14 +606,238 @@ static int for_each_note_helper(struct int_node *tree, unsigned char n,
        return 0;
 }
 
-void init_notes(const char *notes_ref, int flags)
+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 *sha1)
+{
+               strbuf_addf(buf, "%06o %.*s%c", mode, path_len, path, '\0');
+               strbuf_add(buf, sha1, 20);
+}
+
+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 + 40)); /* 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;
+       unsigned char s[20];
+       if (n) {
+               ret = tree_write_stack_finish_subtree(n);
+               if (ret)
+                       return ret;
+               ret = write_sha1_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);
+               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 unsigned char *sha1)
+{
+       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),
+                        sha1);
+
+       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, 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->sha1);
+                       if (ret)
+                               return ret;
+               }
+               n = n->next;
+       }
+       d->next_non_note = n;
+       return 0;
+}
+
+static int write_each_note(const unsigned char *object_sha1,
+               const unsigned char *note_sha1, 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 <= 40 + 19);
+
+       /* 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_sha1);
+}
+
+struct note_delete_list {
+       struct note_delete_list *next;
+       const unsigned char *sha1;
+};
+
+static int prune_notes_helper(const unsigned char *object_sha1,
+               const unsigned char *note_sha1, char *note_path,
+               void *cb_data)
+{
+       struct note_delete_list **l = (struct note_delete_list **) cb_data;
+       struct note_delete_list *n;
+
+       if (has_sha1_file(object_sha1))
+               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_sha1;
+       *l = n;
+       return 0;
+}
+
+int combine_notes_concatenate(unsigned char *cur_sha1,
+               const unsigned char *new_sha1)
+{
+       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_sha1(new_sha1))
+               new_msg = read_sha1_file(new_sha1, &new_type, &new_len);
+       if (!new_msg || !new_len || new_type != OBJ_BLOB) {
+               free(new_msg);
+               return 0;
+       }
+       if (!is_null_sha1(cur_sha1))
+               cur_msg = read_sha1_file(cur_sha1, &cur_type, &cur_len);
+       if (!cur_msg || !cur_len || cur_type != OBJ_BLOB) {
+               free(cur_msg);
+               free(new_msg);
+               hashcpy(cur_sha1, new_sha1);
+               return 0;
+       }
+
+       /* we will separate the notes by a newline anyway */
+       if (cur_msg[cur_len - 1] == '\n')
+               cur_len--;
+
+       /* concatenate cur_msg and new_msg into buf */
+       buf_len = cur_len + 1 + new_len;
+       buf = (char *) xmalloc(buf_len);
+       memcpy(buf, cur_msg, cur_len);
+       buf[cur_len] = '\n';
+       memcpy(buf + cur_len + 1, new_msg, new_len);
+       free(cur_msg);
+       free(new_msg);
+
+       /* create a new blob object from buf */
+       ret = write_sha1_file(buf, buf_len, blob_type, cur_sha1);
+       free(buf);
+       return ret;
+}
+
+int combine_notes_overwrite(unsigned char *cur_sha1,
+               const unsigned char *new_sha1)
+{
+       hashcpy(cur_sha1, new_sha1);
+       return 0;
+}
+
+int combine_notes_ignore(unsigned char *cur_sha1,
+               const unsigned char *new_sha1)
+{
+       return 0;
+}
+
+void init_notes(struct notes_tree *t, const char *notes_ref,
+               combine_notes_fn combine_notes, int flags)
 {
        unsigned char sha1[20], object_sha1[20];
        unsigned mode;
        struct leaf_node root_tree;
 
-       assert(!initialized);
-       initialized = 1;
+       if (!t)
+               t = &default_notes_tree;
+       assert(!t->initialized);
 
        if (!notes_ref)
                notes_ref = getenv(GIT_NOTES_REF_ENVIRONMENT);
@@ -556,6 +846,16 @@ void init_notes(const char *notes_ref, int flags)
        if (!notes_ref)
                notes_ref = GIT_NOTES_DEFAULT_REF;
 
+       if (!combine_notes)
+               combine_notes = combine_notes_concatenate;
+
+       t->root = (struct int_node *) xcalloc(sizeof(struct int_node), 1);
+       t->first_non_note = NULL;
+       t->prev_non_note = NULL;
+       t->ref = notes_ref ? xstrdup(notes_ref) : NULL;
+       t->combine_notes = combine_notes;
+       t->initialized = 1;
+
        if (flags & NOTES_INIT_EMPTY || !notes_ref ||
            read_ref(notes_ref, object_sha1))
                return;
@@ -565,54 +865,121 @@ void init_notes(const char *notes_ref, int flags)
 
        hashclr(root_tree.key_sha1);
        hashcpy(root_tree.val_sha1, sha1);
-       load_subtree(&root_tree, &root_node, 0);
+       load_subtree(t, &root_tree, t->root, 0);
 }
 
-void add_note(const unsigned char *object_sha1, const unsigned char *note_sha1)
+void add_note(struct notes_tree *t, const unsigned char *object_sha1,
+               const unsigned char *note_sha1, combine_notes_fn combine_notes)
 {
        struct leaf_node *l;
 
-       assert(initialized);
+       if (!t)
+               t = &default_notes_tree;
+       assert(t->initialized);
+       if (!combine_notes)
+               combine_notes = t->combine_notes;
        l = (struct leaf_node *) xmalloc(sizeof(struct leaf_node));
        hashcpy(l->key_sha1, object_sha1);
        hashcpy(l->val_sha1, note_sha1);
-       note_tree_insert(&root_node, 0, l, PTR_TYPE_NOTE);
+       note_tree_insert(t, t->root, 0, l, PTR_TYPE_NOTE, combine_notes);
 }
 
-void remove_note(const unsigned char *object_sha1)
+void remove_note(struct notes_tree *t, const unsigned char *object_sha1)
 {
        struct leaf_node l;
 
-       assert(initialized);
+       if (!t)
+               t = &default_notes_tree;
+       assert(t->initialized);
        hashcpy(l.key_sha1, object_sha1);
        hashclr(l.val_sha1);
-       return note_tree_remove(&root_node, 0, &l);
+       return note_tree_remove(t, t->root, 0, &l);
 }
 
-const unsigned char *get_note(const unsigned char *object_sha1)
+const unsigned char *get_note(struct notes_tree *t,
+               const unsigned char *object_sha1)
 {
        struct leaf_node *found;
 
-       assert(initialized);
-       found = note_tree_find(&root_node, 0, object_sha1);
+       if (!t)
+               t = &default_notes_tree;
+       assert(t->initialized);
+       found = note_tree_find(t, t->root, 0, object_sha1);
        return found ? found->val_sha1 : NULL;
 }
 
-int for_each_note(int flags, each_note_fn fn, void *cb_data)
+int for_each_note(struct notes_tree *t, int flags, each_note_fn fn,
+               void *cb_data)
 {
-       assert(initialized);
-       return for_each_note_helper(&root_node, 0, 0, flags, fn, 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);
 }
 
-void free_notes(void)
+int write_notes_tree(struct notes_tree *t, unsigned char *result)
 {
-       note_tree_free(&root_node);
-       memset(&root_node, 0, sizeof(struct int_node));
-       initialized = 0;
+       struct tree_write_stack root;
+       struct write_each_note_data cb_data;
+       int ret;
+
+       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 + 40)); /* 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 */
+       ret = for_each_note(t, FOR_EACH_NOTE_DONT_UNPACK_SUBTREES |
+                               FOR_EACH_NOTE_YIELD_SUBTREES,
+                       write_each_note, &cb_data) ||
+               write_each_non_note_until(NULL, &cb_data) ||
+               tree_write_stack_finish_subtree(&root) ||
+               write_sha1_file(root.buf.buf, root.buf.len, tree_type, result);
+       strbuf_release(&root.buf);
+       return ret;
+}
+
+void prune_notes(struct notes_tree *t)
+{
+       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) {
+               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));
 }
 
-void format_note(const unsigned char *object_sha1, struct strbuf *sb,
-               const char *output_encoding, int flags)
+void format_note(struct notes_tree *t, const unsigned char *object_sha1,
+               struct strbuf *sb, const char *output_encoding, int flags)
 {
        static const char utf8[] = "utf-8";
        const unsigned char *sha1;
@@ -620,10 +987,12 @@ void format_note(const unsigned char *object_sha1, struct strbuf *sb,
        unsigned long linelen, msglen;
        enum object_type type;
 
-       if (!initialized)
-               init_notes(NULL, 0);
+       if (!t)
+               t = &default_notes_tree;
+       if (!t->initialized)
+               init_notes(t, NULL, NULL, 0);
 
-       sha1 = get_note(object_sha1);
+       sha1 = get_note(t, object_sha1);
        if (!sha1)
                return;