[PATCH 3/5] WIP: fs: ext4: support unlinkat_s() for secure deletion of files

[Alexander Holler <holler@ahsoftware.de>]

Signed-off-by: Alexander Holler <holler@ahsoftware.de>
---
 fs/ext4/ext4.h    |  2 ++
 fs/ext4/mballoc.c | 25 +++++++++++++++++++++++--
 fs/ext4/super.c   | 12 ++++++++++++
 3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index c55a1fa..e66507c 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1342,6 +1342,8 @@ struct ext4_sb_info {
 	struct ratelimit_state s_err_ratelimit_state;
 	struct ratelimit_state s_warning_ratelimit_state;
 	struct ratelimit_state s_msg_ratelimit_state;
+
+	atomic_t secure_delete;   /* delete blocks securely? */
 };
 
 static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index dbfe15c..f33416f 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2756,6 +2756,19 @@ static inline int ext4_issue_discard(struct super_block *sb,
 	return sb_issue_discard(sb, discard_block, count, GFP_NOFS, 0);
 }
 
+static inline int ext4_issue_zeroout(struct super_block *sb,
+		ext4_group_t block_group, ext4_grpblk_t cluster, int count)
+{
+	ext4_fsblk_t discard_block;
+
+	discard_block = (EXT4_C2B(EXT4_SB(sb), cluster) +
+			 ext4_group_first_block_no(sb, block_group));
+	count = EXT4_C2B(EXT4_SB(sb), count);
+	//trace_ext4_discard_blocks(sb,
+	//		(unsigned long long) discard_block, count);
+	return sb_issue_zeroout(sb, discard_block, count, GFP_NOFS);
+}
+
 /*
  * This function is called by the jbd2 layer once the commit has finished,
  * so we know we can free the blocks that were released with that commit.
@@ -2764,6 +2777,7 @@ static void ext4_free_data_callback(struct super_block *sb,
 				    struct ext4_journal_cb_entry *jce,
 				    int rc)
 {
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct ext4_free_data *entry = (struct ext4_free_data *)jce;
 	struct ext4_buddy e4b;
 	struct ext4_group_info *db;
@@ -2772,6 +2786,11 @@ static void ext4_free_data_callback(struct super_block *sb,
 	mb_debug(1, "gonna free %u blocks in group %u (0x%p):",
 		 entry->efd_count, entry->efd_group, entry);
 
+
+	// TODO:
+	// if (atomic_read(&sbi->secure_delete) && secure_trim_available)
+	// 	use secure trim
+	// else
 	if (test_opt(sb, DISCARD)) {
 		err = ext4_issue_discard(sb, entry->efd_group,
 					 entry->efd_start_cluster,
@@ -2782,8 +2801,10 @@ static void ext4_free_data_callback(struct super_block *sb,
 				 " with %d", entry->efd_group,
 				 entry->efd_start_cluster,
 				 entry->efd_count, err);
-	}
-
+	} else if (atomic_read(&sbi->secure_delete))
+		ext4_issue_zeroout(sb, entry->efd_group,
+					 entry->efd_start_cluster,
+					 entry->efd_count);
 	err = ext4_mb_load_buddy(sb, entry->efd_group, &e4b);
 	/* we expect to find existing buddy because it's pinned */
 	BUG_ON(err != 0);
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2c9e686..f87e3ff 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1100,6 +1100,17 @@ static const struct quotactl_ops ext4_qctl_sysfile_operations = {
 };
 #endif
 
+static void ext4_set_secure_delete(struct super_block *sb, bool secure)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	// TODO: will overflow with a very large number of
+	// concurrent calls of unlinkat_s().
+	if (secure)
+		atomic_inc(&sbi->secure_delete);
+	else
+		atomic_dec(&sbi->secure_delete);
+}
+
 static const struct super_operations ext4_sops = {
 	.alloc_inode	= ext4_alloc_inode,
 	.destroy_inode	= ext4_destroy_inode,
@@ -1119,6 +1130,7 @@ static const struct super_operations ext4_sops = {
 	.quota_write	= ext4_quota_write,
 #endif
 	.bdev_try_to_free_page = bdev_try_to_free_page,
+	.set_secure_delete = ext4_set_secure_delete,
 };
 
 static const struct export_operations ext4_export_ops = {
-- 
2.1.0