ubifs: Implement UBIFS_FLG_DOUBLE_HASH

This feature flag indicates that all directory entry nodes have a 32bit
cookie set and therefore UBIFS is allowed to perform lookups by hash.
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/journal.c

@@ -501,6 +501,14 @@ static void mark_inode_clean(struct ubifs_info *c, struct ubifs_inode *ui)
 	ui->dirty = 0;
 }
 
+static void set_dent_cookie(struct ubifs_info *c, struct ubifs_dent_node *dent)
+{
+	if (c->double_hash)
+		dent->cookie = prandom_u32();
+	else
+		dent->cookie = 0;
+}
+
 /**
  * ubifs_jnl_update - update inode.
  * @c: UBIFS file-system description object
@@ -589,7 +597,7 @@ int ubifs_jnl_update(struct ubifs_info *c, const struct inode *dir,
 	dent->nlen = cpu_to_le16(fname_len(nm));
 	memcpy(dent->name, fname_name(nm), fname_len(nm));
 	dent->name[fname_len(nm)] = '\0';
-	dent->cookie = prandom_u32();
+	set_dent_cookie(c, dent);
 
 	zero_dent_node_unused(dent);
 	ubifs_prep_grp_node(c, dent, dlen, 0);
@@ -1125,7 +1133,7 @@ int ubifs_jnl_rename(struct ubifs_info *c, const struct inode *old_dir,
 	dent->nlen = cpu_to_le16(fname_len(new_nm));
 	memcpy(dent->name, fname_name(new_nm), fname_len(new_nm));
 	dent->name[fname_len(new_nm)] = '\0';
-	dent->cookie = prandom_u32();
+	set_dent_cookie(c, dent);
 	zero_dent_node_unused(dent);
 	ubifs_prep_grp_node(c, dent, dlen1, 0);
 
@@ -1144,7 +1152,7 @@ int ubifs_jnl_rename(struct ubifs_info *c, const struct inode *old_dir,
 	dent2->nlen = cpu_to_le16(fname_len(old_nm));
 	memcpy(dent2->name, fname_name(old_nm), fname_len(old_nm));
 	dent2->name[fname_len(old_nm)] = '\0';
-	dent2->cookie = prandom_u32();
+	set_dent_cookie(c, dent2);
 	zero_dent_node_unused(dent2);
 	ubifs_prep_grp_node(c, dent2, dlen2, 0);
 

fs/ubifs/sb.c

@@ -163,6 +163,7 @@ static int create_default_filesystem(struct ubifs_info *c)
 	tmp64 = (long long)max_buds * c->leb_size;
 	if (big_lpt)
 		sup_flags |= UBIFS_FLG_BIGLPT;
+	sup_flags |= UBIFS_FLG_DOUBLE_HASH;
 
 	sup->ch.node_type  = UBIFS_SB_NODE;
 	sup->key_hash      = UBIFS_KEY_HASH_R5;
@@ -620,6 +621,7 @@ int ubifs_read_superblock(struct ubifs_info *c)
 	memcpy(&c->uuid, &sup->uuid, 16);
 	c->big_lpt = !!(sup_flags & UBIFS_FLG_BIGLPT);
 	c->space_fixup = !!(sup_flags & UBIFS_FLG_SPACE_FIXUP);
+	c->double_hash = !!(sup_flags & UBIFS_FLG_DOUBLE_HASH);
 
 	/* Automatically increase file system size to the maximum size */
 	c->old_leb_cnt = c->leb_cnt;

fs/ubifs/tnc.c

@@ -1930,6 +1930,9 @@ int ubifs_tnc_lookup_dh(struct ubifs_info *c, const union ubifs_key *key,
 	int err;
 	const struct ubifs_dent_node *dent = node;
 
+	if (!c->double_hash)
+		return -EOPNOTSUPP;
+
 	/*
 	 * We assume that in most of the cases there are no name collisions and
 	 * 'ubifs_tnc_lookup()' returns us the right direntry.

fs/ubifs/ubifs-media.h

@@ -418,10 +418,13 @@ enum {
  *
  * UBIFS_FLG_BIGLPT: if "big" LPT model is used if set
  * UBIFS_FLG_SPACE_FIXUP: first-mount "fixup" of free space within LEBs needed
+ * UBIFS_FLG_DOUBLE_HASH: store a 32bit cookie in directory entry nodes to
+ *			  support 64bit cookies for lookups by hash
  */
 enum {
 	UBIFS_FLG_BIGLPT = 0x02,
 	UBIFS_FLG_SPACE_FIXUP = 0x04,
+	UBIFS_FLG_DOUBLE_HASH = 0x08,
 };
 
 /**

fs/ubifs/ubifs.h

@@ -1006,6 +1006,7 @@ struct ubifs_debug_info;
  *
  * @big_lpt: flag that LPT is too big to write whole during commit
  * @space_fixup: flag indicating that free space in LEBs needs to be cleaned up
+ * @double_hash: flag indicating that we can do lookups by hash
  * @no_chk_data_crc: do not check CRCs when reading data nodes (except during
  *                   recovery)
  * @bulk_read: enable bulk-reads
@@ -1248,6 +1249,7 @@ struct ubifs_info {
 
 	unsigned int big_lpt:1;
 	unsigned int space_fixup:1;
+	unsigned int double_hash:1;
 	unsigned int no_chk_data_crc:1;
 	unsigned int bulk_read:1;
 	unsigned int default_compr:2;