Clearly specify how combine_notes functions are expected to handle null_sha1
in input, and how they may set the result to null_sha1 in order to cause
the removal of a note.
Also document that passing note_sha1 == null_sha1 to add_note() is usually
a no-op, except in cases where combining it with an existing note yields a
new/changed result.
The only functional changes in this patch concern the handling of null_sha1
in notes_tree_insert(). Otherwise the patch consists solely of reordering
functions in notes.c to avoid use-before-declaration, and adding
documentation to notes.h.
Signed-off-by: Johan Herland <johan@xxxxxxxxxxx>
---
notes.c | 158 +++++++++++++++++++++++++++++++++-----------------------------
notes.h | 16 ++++++-
2 files changed, 99 insertions(+), 75 deletions(-)
diff --git a/notes.c b/notes.c
index 79fd850..9e92021 100644
--- a/notes.c
+++ b/notes.c
@@ -150,6 +150,79 @@ static struct leaf_node *note_tree_find(struct notes_tree *t,
}
/*
+ * 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 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];
+ }
+ }
+
+ /* 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.
+ * - 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[20];
+ unsigned char i, j;
+ 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)
+ return; /* type mismatch, nothing to remove */
+ l = (struct leaf_node *) CLR_PTR_TYPE(*p);
+ if (hashcmp(l->key_sha1, entry->key_sha1))
+ return; /* key mismatch, nothing to remove */
+
+ /* we have found a matching entry */
+ 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_sha1);
+ 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_sha1)))
+ 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
@@ -175,7 +248,10 @@ static void note_tree_insert(struct notes_tree *t, struct int_node *tree,
switch (GET_PTR_TYPE(*p)) {
case PTR_TYPE_NULL:
assert(!*p);
- *p = SET_PTR_TYPE(entry, type);
+ if (is_null_sha1(entry->val_sha1))
+ free(entry);
+ else
+ *p = SET_PTR_TYPE(entry, type);
return;
case PTR_TYPE_NOTE:
switch (type) {
@@ -191,6 +267,9 @@ static void note_tree_insert(struct notes_tree *t, struct int_node *tree,
sha1_to_hex(l->val_sha1),
sha1_to_hex(entry->val_sha1),
sha1_to_hex(l->key_sha1));
+
+ if (is_null_sha1(l->val_sha1))
+ note_tree_remove(t, tree, n, entry);
free(entry);
return;
}
@@ -222,6 +301,10 @@ static void note_tree_insert(struct notes_tree *t, struct int_node *tree,
/* non-matching leaf_node */
assert(GET_PTR_TYPE(*p) == PTR_TYPE_NOTE ||
GET_PTR_TYPE(*p) == PTR_TYPE_SUBTREE);
+ if (is_null_sha1(entry->val_sha1)) { /* skip insertion of empty note */
+ free(entry);
+ return;
+ }
new_node = (struct int_node *) xcalloc(sizeof(struct int_node), 1);
note_tree_insert(t, new_node, n + 1, l, GET_PTR_TYPE(*p),
combine_notes);
@@ -229,79 +312,6 @@ static void note_tree_insert(struct notes_tree *t, struct int_node *tree,
note_tree_insert(t, new_node, n + 1, entry, type, combine_notes);
}
-/*
- * 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 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];
- }
- }
-
- /* 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.
- * - 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[20];
- unsigned char i, j;
- 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)
- return; /* type mismatch, nothing to remove */
- l = (struct leaf_node *) CLR_PTR_TYPE(*p);
- if (hashcmp(l->key_sha1, entry->key_sha1))
- return; /* key mismatch, nothing to remove */
-
- /* we have found a matching entry */
- 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_sha1);
- 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_sha1)))
- i--;
-}
-
/* Free the entire notes data contained in the given tree */
static void note_tree_free(struct int_node *tree)
{
diff --git a/notes.h b/notes.h
index 20db42f..79ea797 100644
--- a/notes.h
+++ b/notes.h
@@ -12,7 +12,10 @@
* resulting SHA1 into the first SHA1 argument (cur_sha1). A non-zero return
* value indicates failure.
*
- * The two given SHA1s must both be non-NULL and different from each other.
+ * The two given SHA1s shall both be non-NULL and different from each other.
+ * Either of them (but not both) may be == null_sha1, which indicates an
+ * empty/non-existent note. If the resulting SHA1 (cur_sha1) is == null_sha1,
+ * the note will be removed from the notes tree.
*
* The default combine_notes function (you get this when passing NULL) is
* combine_notes_concatenate(), which appends the contents of the new note to
@@ -90,6 +93,17 @@ void init_notes(struct notes_tree *t, const char *notes_ref,
/*
* Add the given note object to the given notes_tree structure
*
+ * If there already exists a note for the given object_sha1, the given
+ * combine_notes function is invoked to break the tie. If not given (i.e.
+ * combine_notes == NULL), the default combine_notes function for the given
+ * notes_tree is used.
+ *
+ * Passing note_sha1 == null_sha1 indicates the addition of an
+ * empty/non-existent note. This is a (potentially expensive) no-op unless
+ * there already exists a note for the given object_sha1, AND combining that
+ * note with the empty note (using the given combine_notes function) results
+ * in a new/changed note.
+ *
* IMPORTANT: The changes made by add_note() to the given notes_tree structure
* are not persistent until a subsequent call to write_notes_tree() returns
* zero.
--
1.7.2.220.gea1d3
--
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