[PATCH v3 01/12] ftrfs: add on-disk format and in-memory data structures

Aurelien DESBRIERES
2026-04-14T10:07:31Z

Add the core header defining FTRFS on-disk layout and in-memory
VFS structures.

On-disk layout:
Block 0 : superblock (magic 0x46545246, CRC32-protected)
Block 1..N : inode table (128 bytes/inode, CRC32 per inode)
Block N+1..end : data blocks (CRC32 per block, RS FEC planned)

Structures:
ftrfs_super_block : on-disk superblock
ftrfs_inode : on-disk inode (12 direct + 1 indirect + 1 dindirect)
ftrfs_dir_entry : on-disk directory entry (256-byte name)
ftrfs_sb_info : in-memory superblock info (VFS sb->s_fs_info)
ftrfs_inode_info : in-memory inode (embedded VFS inode)

FTRFS targets POSIX-compatible block devices (MRAM, NOR flash, eMMC)
for use in radiation-intensive environments (space applications).

Signed-off-by: Aurelien DESBRIERES <aurelien@hackers.camp>
---
fs/ftrfs/ftrfs.h | 168 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 168 insertions(+)
create mode 100644 fs/ftrfs/ftrfs.h

diff --git a/fs/ftrfs/ftrfs.h b/fs/ftrfs/ftrfs.h
new file mode 100644
index 000000000000..82502c9fb07d
--- /dev/null
+++ b/fs/ftrfs/ftrfs.h
@@ -0,0 +1,168 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * FTRFS — Fault-Tolerant Radiation-Robust Filesystem
+ * Based on: Fuchs, Langer, Trinitis — ARCS 2015
+ *
+ * Author: roastercode - Aurelien DESBRIERES <aurelien@hackers.camp>
+ */
+
+#ifndef _FTRFS_H
+#define _FTRFS_H
+
+#include <linux/fs.h>
+#include <linux/fs_context.h>
+#include <linux/types.h>
+
+/* Magic number: 'FTRF' */
+#define FTRFS_MAGIC 0x46545246
+
+/* Block size: 4096 bytes */
+#define FTRFS_BLOCK_SIZE 4096
+#define FTRFS_BLOCK_SHIFT 12
+
+/* RS FEC: 16 parity bytes per 239-byte subblock (RS(255,239)) */
+#define FTRFS_RS_PARITY 16
+#define FTRFS_SUBBLOCK_DATA 239
+#define FTRFS_SUBBLOCK_TOTAL (FTRFS_SUBBLOCK_DATA + FTRFS_RS_PARITY)
+
+/* Filesystem limits */
+#define FTRFS_MAX_FILENAME 255
+#define FTRFS_DIRECT_BLOCKS 12
+#define FTRFS_INDIRECT_BLOCKS 1
+#define FTRFS_DINDIRECT_BLOCKS 1
+
+/*
+ * On-disk superblock — block 0
+ * Total size: fits in one 4096-byte block
+ */
+struct ftrfs_super_block {
+ __le32 s_magic; /* FTRFS_MAGIC */
+ __le32 s_block_size; /* Block size in bytes */
+ __le64 s_block_count; /* Total blocks */
+ __le64 s_free_blocks; /* Free blocks */
+ __le64 s_inode_count; /* Total inodes */
+ __le64 s_free_inodes; /* Free inodes */
+ __le64 s_inode_table_blk; /* Block where inode table starts */
+ __le64 s_data_start_blk; /* First data block */
+ __le32 s_version; /* Filesystem version */
+ __le32 s_flags; /* Flags */
+ __le32 s_crc32; /* CRC32 of this superblock */
+ __u8 s_uuid[16]; /* UUID */
+ __u8 s_label[32]; /* Volume label */
+ __u8 s_pad[3948]; /* Padding to 4096 bytes */
+} __packed;
+
+/*
+ * On-disk inode
+ * Size: 128 bytes
+ */
+struct ftrfs_inode {
+ __le16 i_mode; /* File mode */
+ __le16 i_uid; /* Owner UID */
+ __le16 i_gid; /* Owner GID */
+ __le16 i_nlink; /* Hard link count */
+ __le64 i_size; /* File size in bytes */
+ __le64 i_atime; /* Access time (ns) */
+ __le64 i_mtime; /* Modification time (ns) */
+ __le64 i_ctime; /* Change time (ns) */
+ __le32 i_blocks; /* Block count */
+ __le32 i_flags; /* Inode flags */
+ __le64 i_direct[FTRFS_DIRECT_BLOCKS]; /* Direct block pointers */
+ __le64 i_indirect; /* Single indirect */
+ __le64 i_dindirect; /* Double indirect */
+ __le32 i_crc32; /* CRC32 of inode */
+ __u8 i_pad[2]; /* Padding to 128 bytes */
+} __packed;
+
+/* Inode flags */
+#define FTRFS_INODE_FL_RS_ENABLED 0x0001 /* RS FEC enabled */
+#define FTRFS_INODE_FL_VERIFIED 0x0002 /* Integrity verified */
+
+/*
+ * On-disk directory entry
+ */
+struct ftrfs_dir_entry {
+ __le64 d_ino; /* Inode number */
+ __le16 d_rec_len; /* Record length */
+ __u8 d_name_len; /* Name length */
+ __u8 d_file_type; /* File type */
+ char d_name[FTRFS_MAX_FILENAME + 1]; /* Filename */
+} __packed;
+
+/*
+ * In-memory superblock info (stored in sb->s_fs_info)
+ */
+struct ftrfs_sb_info {
+ /* Block allocator */
+ unsigned long *s_block_bitmap; /* In-memory free block bitmap */
+ unsigned long s_nblocks; /* Number of data blocks */
+ unsigned long s_data_start; /* First data block number */
+ struct ftrfs_super_block *s_ftrfs_sb; /* On-disk superblock copy */
+ struct buffer_head *s_sbh; /* Buffer head for superblock */
+ spinlock_t s_lock; /* Superblock lock */
+ unsigned long s_free_blocks;
+ unsigned long s_free_inodes;
+};
+
+/*
+ * In-memory inode info (embedded in VFS inode via container_of)
+ */
+struct ftrfs_inode_info {
+ __le64 i_direct[FTRFS_DIRECT_BLOCKS];
+ __le64 i_indirect;
+ __le64 i_dindirect;
+ __u32 i_flags;
+ struct inode vfs_inode; /* Must be last */
+};
+
+static inline struct ftrfs_inode_info *FTRFS_I(struct inode *inode)
+{
+ return container_of(inode, struct ftrfs_inode_info, vfs_inode);
+}
+
+static inline struct ftrfs_sb_info *FTRFS_SB(struct super_block *sb)
+{
+ return sb->s_fs_info;
+}
+
+/* Function prototypes */
+/* super.c */
+int ftrfs_fill_super(struct super_block *sb, struct fs_context *fc);
+
+/* inode.c */
+struct inode *ftrfs_iget(struct super_block *sb, unsigned long ino);
+struct inode *ftrfs_new_inode(struct inode *dir, umode_t mode);
+
+/* dir.c */
+extern const struct file_operations ftrfs_dir_operations;
+extern const struct inode_operations ftrfs_dir_inode_operations;
+
+/* file.c */
+extern const struct file_operations ftrfs_file_operations;
+extern const struct inode_operations ftrfs_file_inode_operations;
+
+/* edac.c */
+__u32 ftrfs_crc32(const void *buf, size_t len);
+int ftrfs_rs_encode(uint8_t *data, uint8_t *parity);
+int ftrfs_rs_decode(uint8_t *data, uint8_t *parity);
+
+/* block.c */
+
+#endif /* _FTRFS_H */
+
+/*
+ */
+
+/* alloc.c */
+int ftrfs_setup_bitmap(struct super_block *sb);
+void ftrfs_destroy_bitmap(struct super_block *sb);
+u64 ftrfs_alloc_block(struct super_block *sb);
+void ftrfs_free_block(struct super_block *sb, u64 block);
+u64 ftrfs_alloc_inode_num(struct super_block *sb);
+
+/* dir.c */
+struct dentry *ftrfs_lookup(struct inode *dir, struct dentry *dentry,
+ unsigned int flags);
+
+/* namei.c */
+int ftrfs_write_inode(struct inode *inode, struct writeback_control *wbc);
--
2.52.0