new file mode 100644
@@ -0,0 +1,242 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * composefs
+ *
+ * Copyright (C) 2021 Giuseppe Scrivano
+ * Copyright (C) 2022 Alexander Larsson
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef _CFS_H
+#define _CFS_H
+
+#include <asm/byteorder.h>
+#include <crypto/sha2.h>
+#include <linux/fs.h>
+#include <linux/stat.h>
+#include <linux/types.h>
+
+#define CFS_VERSION 1
+
+#define CFS_MAGIC 0xc078629aU
+
+#define CFS_MAX_DIR_CHUNK_SIZE 4096
+#define CFS_MAX_XATTRS_SIZE 4096
+
+static inline u16 cfs_u16_to_file(u16 val)
+{
+ return cpu_to_le16(val);
+}
+
+static inline u32 cfs_u32_to_file(u32 val)
+{
+ return cpu_to_le32(val);
+}
+
+static inline u64 cfs_u64_to_file(u64 val)
+{
+ return cpu_to_le64(val);
+}
+
+static inline u16 cfs_u16_from_file(u16 val)
+{
+ return le16_to_cpu(val);
+}
+
+static inline u32 cfs_u32_from_file(u32 val)
+{
+ return le32_to_cpu(val);
+}
+
+static inline u64 cfs_u64_from_file(u64 val)
+{
+ return le64_to_cpu(val);
+}
+
+static inline int cfs_xdigit_value(char c)
+{
+ if (c >= '0' && c <= '9')
+ return c - '0';
+ if (c >= 'A' && c <= 'F')
+ return c - 'A' + 10;
+ if (c >= 'a' && c <= 'f')
+ return c - 'a' + 10;
+ return -1;
+}
+
+static inline int cfs_digest_from_payload(const char *payload,
+ size_t payload_len,
+ u8 digest_out[SHA256_DIGEST_SIZE])
+{
+ const char *p, *end;
+ u8 last_digit = 0;
+ int digit = 0;
+ size_t n_nibbles = 0;
+
+ end = payload + payload_len;
+ for (p = payload; p != end; p++) {
+ /* Skip subdir structure */
+ if (*p == '/')
+ continue;
+
+ /* Break at (and ignore) extension */
+ if (*p == '.')
+ break;
+
+ if (n_nibbles == SHA256_DIGEST_SIZE * 2)
+ return -1; /* Too long */
+
+ digit = cfs_xdigit_value(*p);
+ if (digit == -1)
+ return -1; /* Not hex digit */
+
+ n_nibbles++;
+ if ((n_nibbles % 2) == 0) {
+ digest_out[n_nibbles / 2 - 1] =
+ (last_digit << 4) | digit;
+ }
+ last_digit = digit;
+ }
+
+ if (n_nibbles != SHA256_DIGEST_SIZE * 2)
+ return -1; /* Too short */
+
+ return 0;
+}
+
+struct cfs_vdata_s {
+ u64 off;
+ u32 len;
+} __packed;
+
+struct cfs_header_s {
+ u8 version;
+ u8 unused1;
+ u16 unused2;
+
+ u32 magic;
+ u64 data_offset;
+ u64 root_inode;
+
+ u64 unused3[2];
+} __packed;
+
+enum cfs_inode_flags {
+ CFS_INODE_FLAGS_NONE = 0,
+ CFS_INODE_FLAGS_PAYLOAD = 1 << 0,
+ CFS_INODE_FLAGS_MODE = 1 << 1,
+ CFS_INODE_FLAGS_NLINK = 1 << 2,
+ CFS_INODE_FLAGS_UIDGID = 1 << 3,
+ CFS_INODE_FLAGS_RDEV = 1 << 4,
+ CFS_INODE_FLAGS_TIMES = 1 << 5,
+ CFS_INODE_FLAGS_TIMES_NSEC = 1 << 6,
+ CFS_INODE_FLAGS_LOW_SIZE = 1 << 7, /* Low 32bit of st_size */
+ CFS_INODE_FLAGS_HIGH_SIZE = 1 << 8, /* High 32bit of st_size */
+ CFS_INODE_FLAGS_XATTRS = 1 << 9,
+ CFS_INODE_FLAGS_DIGEST = 1
+ << 10, /* fs-verity sha256 digest of content */
+ CFS_INODE_FLAGS_DIGEST_FROM_PAYLOAD =
+ 1 << 11, /* Compute digest from payload */
+};
+
+#define CFS_INODE_FLAG_CHECK(_flag, _name) \
+ (((_flag) & (CFS_INODE_FLAGS_##_name)) != 0)
+#define CFS_INODE_FLAG_CHECK_SIZE(_flag, _name, _size) \
+ (CFS_INODE_FLAG_CHECK(_flag, _name) ? (_size) : 0)
+
+#define CFS_INODE_DEFAULT_MODE 0100644
+#define CFS_INODE_DEFAULT_NLINK 1
+#define CFS_INODE_DEFAULT_NLINK_DIR 2
+#define CFS_INODE_DEFAULT_UIDGID 0
+#define CFS_INODE_DEFAULT_RDEV 0
+#define CFS_INODE_DEFAULT_TIMES 0
+
+struct cfs_inode_s {
+ u32 flags;
+
+ /* Optional data: (selected by flags) */
+
+ /* This is the size of the type specific data that comes directly after
+ * the inode in the file. Of this type:
+ *
+ * directory: cfs_dir_s
+ * regular file: the backing filename
+ * symlink: the target link
+ *
+ * Canonically payload_length is 0 for empty dir/file/symlink.
+ */
+ u32 payload_length;
+
+ u32 st_mode; /* File type and mode. */
+ u32 st_nlink; /* Number of hard links, only for regular files. */
+ u32 st_uid; /* User ID of owner. */
+ u32 st_gid; /* Group ID of owner. */
+ u32 st_rdev; /* Device ID (if special file). */
+ u64 st_size; /* Size of file, only used for regular files */
+
+ struct cfs_vdata_s xattrs; /* ref to variable data */
+
+ u8 digest[SHA256_DIGEST_SIZE]; /* fs-verity digest */
+
+ struct timespec64 st_mtim; /* Time of last modification. */
+ struct timespec64 st_ctim; /* Time of last status change. */
+};
+
+static inline u32 cfs_inode_encoded_size(u32 flags)
+{
+ return sizeof(u32) /* flags */ +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, PAYLOAD, sizeof(u32)) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, MODE, sizeof(u32)) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, NLINK, sizeof(u32)) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, UIDGID,
+ sizeof(u32) + sizeof(u32)) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, RDEV, sizeof(u32)) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, TIMES, sizeof(u64) * 2) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, TIMES_NSEC, sizeof(u32) * 2) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, LOW_SIZE, sizeof(u32)) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, HIGH_SIZE, sizeof(u32)) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, XATTRS,
+ sizeof(u64) + sizeof(u32)) +
+ CFS_INODE_FLAG_CHECK_SIZE(flags, DIGEST, SHA256_DIGEST_SIZE);
+}
+
+struct cfs_dentry_s {
+ /* Index of struct cfs_inode_s */
+ u64 inode_index;
+ u8 d_type;
+ u8 name_len;
+ u16 name_offset;
+} __packed;
+
+struct cfs_dir_chunk_s {
+ u16 n_dentries;
+ u16 chunk_size;
+ u64 chunk_offset;
+} __packed;
+
+struct cfs_dir_s {
+ u32 n_chunks;
+ struct cfs_dir_chunk_s chunks[];
+} __packed;
+
+#define cfs_dir_size(_n_chunks) \
+ (sizeof(struct cfs_dir_s) + \
+ (_n_chunks) * sizeof(struct cfs_dir_chunk_s))
+
+/* xattr representation. */
+struct cfs_xattr_element_s {
+ u16 key_length;
+ u16 value_length;
+} __packed;
+
+struct cfs_xattr_header_s {
+ u16 n_attr;
+ struct cfs_xattr_element_s attr[0];
+} __packed;
+
+#define cfs_xattr_header_size(_n_element) \
+ (sizeof(struct cfs_xattr_header_s) + \
+ (_n_element) * sizeof(struct cfs_xattr_element_s))
+
+#endif