[RFC PATCH 01/10] ftrfs: add on-disk format and in-memory data structures

[Aurelien DESBRIERES <aurelien@hackers.camp>]

From: Aurélien DESBRIERES <aurelien@hackers.camp>

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: Aurélien 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 000000000..82502c9fb
--- /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