[PATCH 2/5] WIP: fs: fat: support unlinkat_s() for secure deletion of files

[Alexander Holler <holler@ahsoftware.de>]

Signed-off-by: Alexander Holler <holler@ahsoftware.de>
---
 fs/fat/fat.h    |  1 +
 fs/fat/fatent.c | 20 ++++++++++++++++++++
 fs/fat/inode.c  | 13 +++++++++++++
 3 files changed, 34 insertions(+)

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index e0c4ba3..b9febda 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -81,6 +81,7 @@ struct msdos_sb_info {
 	unsigned int prev_free;      /* previously allocated cluster number */
 	unsigned int free_clusters;  /* -1 if undefined */
 	unsigned int free_clus_valid; /* is free_clusters valid? */
+	atomic_t secure_delete;   /* delete blocks securely? */
 	struct fat_mount_options options;
 	struct nls_table *nls_disk;   /* Codepage used on disk */
 	struct nls_table *nls_io;     /* Charset used for input and display */
diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index 260705c..b3b9c11 100644
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -575,6 +575,10 @@ int fat_free_clusters(struct inode *inode, int cluster)
 			goto error;
 		}
 
+		// TODO:
+		// if (atomic_read(&sbi->secure_delete) && secure_trim_available)
+		// 	use secure trim
+		// else
 		if (sbi->options.discard) {
 			/*
 			 * Issue discard for the sectors we no longer
@@ -591,6 +595,22 @@ int fat_free_clusters(struct inode *inode, int cluster)
 
 				first_cl = cluster;
 			}
+		} else if (atomic_read(&sbi->secure_delete)) {
+			/*
+			 * Fill blocks with zero for the sectors we no
+			 * longer care about, batching contiguous clusters
+			 * into one request.
+			 */
+			if (cluster != fatent.entry + 1) {
+				int nr_clus = fatent.entry - first_cl + 1;
+
+				sb_issue_zeroout(sb,
+					fat_clus_to_blknr(sbi, first_cl),
+					nr_clus * sbi->sec_per_clus,
+					GFP_NOFS);
+
+				first_cl = cluster;
+			}
 		}
 
 		ops->ent_put(&fatent, FAT_ENT_FREE);
diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 756aead..9073690 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -816,6 +816,17 @@ int fat_sync_inode(struct inode *inode)
 
 EXPORT_SYMBOL_GPL(fat_sync_inode);
 
+static void fat_set_secure_delete(struct super_block *sb, bool secure)
+{
+	struct msdos_sb_info *sbi = MSDOS_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 int fat_show_options(struct seq_file *m, struct dentry *root);
 static const struct super_operations fat_sops = {
 	.alloc_inode	= fat_alloc_inode,
@@ -827,6 +838,7 @@ static const struct super_operations fat_sops = {
 	.remount_fs	= fat_remount,
 
 	.show_options	= fat_show_options,
+	.set_secure_delete = fat_set_secure_delete,
 };
 
 static int fat_show_options(struct seq_file *m, struct dentry *root)
@@ -1580,6 +1592,7 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
 	sbi->root_cluster = 0;
 	sbi->free_clusters = -1;	/* Don't know yet */
 	sbi->free_clus_valid = 0;
+	atomic_set(&sbi->secure_delete, 0);
 	sbi->prev_free = FAT_START_ENT;
 	sb->s_maxbytes = 0xffffffff;
 
-- 
2.1.0