Invent a cunning means of faking plausible atimes for directories,

[sgt/agedu] / trie.c

diff --git a/trie.c b/trie.c
index 7168a9e..1344bdf 100644 (file)
--- a/trie.c
+++ b/trie.c
@@ -392,6 +392,117 @@ void triebuild_free(triebuild *tb)
 }
 
 /* ----------------------------------------------------------------------
+ * Memory-mapped trie modification.
+ */
+
+#define MNODE(t, off, type) \
+    ((struct type *)((char *)(t) + (off)))
+
+static unsigned long long fake_atime_recurse(void *t, struct trie_common *node,
+                                            int last_seen_pathsep)
+{
+    while (node->type == TRIE_STRING) {
+       struct trie_string *st = (struct trie_string *)node;
+       last_seen_pathsep = (st->string[st->stringlen-1] == pathsep);
+       node = MNODE(t, st->subnode, trie_common);
+    }
+
+    if (node->type == TRIE_LEAF) {
+       struct trie_leaf *leaf = (struct trie_leaf *)node;
+       return leaf->file.atime;
+    } else if (assert(node->type == TRIE_SWITCH), 1) {
+       struct trie_switch *sw = (struct trie_switch *)node;
+       const char *chars = (const char *)&sw->sw[sw->len];
+       unsigned long long max = 0, subdir, ret;
+       int i;
+       int slashindex = -1, bareindex = -1;
+
+       /*
+        * First, process all the children of this node whose
+        * switch characters are not \0 or pathsep. We do this in
+        * reverse order so as to maintain best cache locality
+        * (tracking generally backwards through the file), though
+        * it doesn't matter semantically.
+        *
+        * For each of these children, we're just recursing into
+        * it to do any fixups required below it, and amalgamating
+        * the max atimes we get back.
+        */
+       for (i = sw->len; i-- > 0 ;) {
+           if (chars[i] == '\0') {
+               bareindex = i;
+           } else if (chars[i] == pathsep) {
+               slashindex = i;
+           } else {
+               ret = fake_atime_recurse(t, MNODE(t, sw->sw[i].subnode,
+                                                 trie_common), 0);
+               if (max < ret)
+                   max = ret;
+           }
+       }
+
+       /*
+        * Now we have at most two child nodes left to deal with:
+        * one with a slash (or general pathsep) and one with \0.
+        *
+        * If there's a slash node and a bare node, then the slash
+        * node contains precisely everything inside the directory
+        * described by the bare node; so we must retrieve the max
+        * atime for the slash node and use it to fix up the bare
+        * node.
+        *
+        * If there's only a bare node but the pathname leading up
+        * to this point ends in a slash, then _all_ of the child
+        * nodes of this node contain stuff inside the directory
+        * described by the bare node; so we use the whole of the
+        * maximum value we've computed so far to update the bare
+        * node.
+        */
+       if (slashindex >= 0) {
+           ret = fake_atime_recurse(t, MNODE(t, sw->sw[slashindex].subnode,
+                                             trie_common), 1);
+           if (max < ret)
+               max = ret;
+
+           subdir = ret;
+       } else if (last_seen_pathsep) {
+           subdir = max;
+       } else {
+           /* Don't update the bare subnode at all. */
+           subdir = 0;
+       }
+
+       if (bareindex >= 0) {
+           struct trie_leaf *leaf;
+
+           leaf = MNODE(t, sw->sw[bareindex].subnode, trie_leaf);
+
+           if (leaf && leaf->c.type == TRIE_LEAF) {
+               if (leaf->file.atime < subdir)
+                   leaf->file.atime = subdir;
+               ret = leaf->file.atime;
+           } else {
+               /* Shouldn't really happen, but be cautious anyway */
+               ret = fake_atime_recurse(t, &leaf->c, 0);
+           }
+
+           if (max < ret)
+               max = ret;
+       }
+
+       return max;
+    }
+}
+
+void trie_fake_dir_atimes(void *t)
+{
+    struct trie_header *hdr = MNODE(t, 0, trie_header);
+    struct trie_common *node = MNODE(t, hdr->root, trie_common);
+
+    fake_atime_recurse(t, node, 1);
+}
+
+/* ----------------------------------------------------------------------
  * Querying functions.
  */