fs/squashfs: new filesystem

Add support for SquashFS filesystem. Right now, it does not support
compression but support for zlib will be added in a follow-up commit.

Signed-off-by: Joao Marcos Costa <joaomarcos.costa@bootlin.com>

MAINTAINERS

@@ -969,6 +969,12 @@ S:	Maintained
 F:	drivers/spmi/
 F:	include/spmi/
 
+SQUASHFS
+M:	Joao Marcos Costa <joaomarcos.costa@bootlin.com>
+S:	Maintained
+F:	fs/squashfs/
+F:	include/sqfs.h
+
 TARGET_BCMNS3
 M:	Bharat Gooty <bharat.gooty@broadcom.com>
 M:	Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>

common/spl/Kconfig

@@ -577,6 +577,15 @@ config SPL_FS_EXT4
 	  filesystem from within SPL. Support for the underlying block
 	  device (e.g. MMC or USB) must be enabled separately.
 
+config SPL_FS_SQUASHFS
+	bool "Support SquashFS filesystems"
+	select FS_SQUASHFS
+	help
+	  Enable support for SquashFS filesystems with SPL. This permits
+	  U-Boot (or Linux in Falcon mode) to be loaded from a SquashFS
+	  filesystem from within SPL. Support for the underlying block
+	  device (e.g. MMC or USB) must be enabled separately.
+
 config SPL_FS_FAT
 	bool "Support FAT filesystems"
 	select FS_FAT

fs/Kconfig

@@ -22,4 +22,6 @@ source "fs/cramfs/Kconfig"
 
 source "fs/yaffs2/Kconfig"
 
+source "fs/squashfs/Kconfig"
+
 endmenu

fs/Makefile

@@ -9,6 +9,7 @@ obj-$(CONFIG_FS_LOADER) += fs.o
 obj-$(CONFIG_SPL_FS_FAT) += fat/
 obj-$(CONFIG_SPL_FS_EXT4) += ext4/
 obj-$(CONFIG_SPL_FS_CBFS) += cbfs/
+obj-$(CONFIG_SPL_FS_SQUASHFS) += squashfs/
 else
 obj-y				+= fs.o
 
@@ -23,5 +24,6 @@ obj-$(CONFIG_SANDBOX) += sandbox/
 obj-$(CONFIG_CMD_UBIFS) += ubifs/
 obj-$(CONFIG_YAFFS2) += yaffs2/
 obj-$(CONFIG_CMD_ZFS) += zfs/
+obj-$(CONFIG_FS_SQUASHFS) += squashfs/
 endif
 obj-y += fs_internal.o

fs/fs.c

@@ -22,6 +22,7 @@
 #include <div64.h>
 #include <linux/math64.h>
 #include <efi_loader.h>
+#include <squashfs.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -276,6 +277,20 @@ static struct fstype_info fstypes[] = {
 		.mkdir = fs_mkdir_unsupported,
 		.ln = fs_ln_unsupported,
 	},
+#endif
+#if IS_ENABLED(CONFIG_FS_SQUASHFS)
+	{
+		.fstype = FS_TYPE_SQUASHFS,
+		.name = "squashfs",
+		.probe = sqfs_probe,
+		.opendir = sqfs_opendir,
+		.readdir = sqfs_readdir,
+		.ls = fs_ls_generic,
+		.read = sqfs_read,
+		.size = sqfs_size,
+		.close = sqfs_close,
+		.closedir = sqfs_closedir,
+	},
 #endif
 	{
 		.fstype = FS_TYPE_ANY,

fs/squashfs/Kconfig

@@ -0,0 +1,10 @@
+config FS_SQUASHFS
+	bool "Enable SquashFS filesystem support"
+	help
+	  This provides support for reading images from SquashFS filesystem.
+	  Squashfs is a compressed read-only filesystem for Linux.
+	  It uses zlib, lz4, lzo, or xz compression to compress files, inodes
+	  and directories. Squashfs is intended for general read-only
+	  filesystem use, for archival use (i.e. in cases where a .tar.gz file
+	  may be used), and in constrained block device/memory systems (e.g.
+	  embedded systems) where low overhead is needed.

fs/squashfs/Makefile

@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+
+obj-$(CONFIG_$(SPL_)FS_SQUASHFS) = sqfs.o \
+				sqfs_inode.o \
+				sqfs_dir.o \
+				sqfs_decompressor.o

fs/squashfs/sqfs_decompressor.c

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Bootlin
+ *
+ * Author: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
+ */
+
+#include <errno.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "sqfs_decompressor.h"
+#include "sqfs_filesystem.h"
+#include "sqfs_utils.h"
+
+int sqfs_decompress(u16 comp_type, void *dest, unsigned long *dest_len,
+		    void *source, u32 lenp)
+{
+	int ret = 0;
+
+	switch (comp_type) {
+	default:
+		printf("Error: unknown compression type.\n");
+		return -EINVAL;
+	}
+
+	return ret;
+}

fs/squashfs/sqfs_decompressor.h

@@ -0,0 +1,58 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 Bootlin
+ *
+ * Author: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
+ */
+
+#ifndef SQFS_DECOMPRESSOR_H
+#define SQFS_DECOMPRESSOR_H
+
+#include <stdint.h>
+
+#define SQFS_COMP_ZLIB 1
+#define SQFS_COMP_LZMA 2
+#define SQFS_COMP_LZO 3
+#define SQFS_COMP_XZ 4
+#define SQFS_COMP_LZ4 5
+#define SQFS_COMP_ZSTD 6
+
+/* LZMA does not support any compression options */
+
+struct squashfs_gzip_opts {
+	u32 compression_level;
+	u16 window_size;
+	u16 strategies;
+};
+
+struct squashfs_xz_opts {
+	u32 dictionary_size;
+	u32 executable_filters;
+};
+
+struct squashfs_lz4_opts {
+	u32 version;
+	u32 flags;
+};
+
+struct squashfs_zstd_opts {
+	u32 compression_level;
+};
+
+struct squashfs_lzo_opts {
+	u32 algorithm;
+	u32 level;
+};
+
+union squashfs_compression_opts {
+	struct squashfs_gzip_opts *gzip;
+	struct squashfs_xz_opts *xz;
+	struct squashfs_lz4_opts *lz4;
+	struct squashfs_zstd_opts *zstd;
+	struct squashfs_lzo_opts *lzo;
+};
+
+int sqfs_decompress(u16 comp_type, void *dest, unsigned long *dest_len,
+		    void *source, u32 lenp);
+
+#endif /* SQFS_DECOMPRESSOR_H */

fs/squashfs/sqfs_dir.c

@@ -0,0 +1,91 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Bootlin
+ *
+ * Author: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
+ */
+
+#include <errno.h>
+#include <linux/types.h>
+#include <linux/byteorder/little_endian.h>
+#include <linux/byteorder/generic.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "sqfs_filesystem.h"
+#include "sqfs_utils.h"
+
+bool sqfs_is_dir(u16 type)
+{
+	return type == SQFS_DIR_TYPE || type == SQFS_LDIR_TYPE;
+}
+
+/*
+ * Receives a pointer (void *) to a position in the inode table containing the
+ * directory's inode. Returns directory inode offset into the directory table.
+ * m_list contains each metadata block's position, and m_count is the number of
+ * elements of m_list. Those metadata blocks come from the compressed directory
+ * table.
+ */
+int sqfs_dir_offset(void *dir_i, u32 *m_list, int m_count)
+{
+	struct squashfs_base_inode *base = dir_i;
+	struct squashfs_ldir_inode *ldir;
+	struct squashfs_dir_inode *dir;
+	u32 start_block;
+	u16 offset;
+	int j;
+
+	switch (get_unaligned_le16(&base->inode_type)) {
+	case SQFS_DIR_TYPE:
+		dir = (struct squashfs_dir_inode *)base;
+		start_block = get_unaligned_le32(&dir->start_block);
+		offset = get_unaligned_le16(&dir->offset);
+		break;
+	case SQFS_LDIR_TYPE:
+		ldir = (struct squashfs_ldir_inode *)base;
+		start_block = get_unaligned_le32(&ldir->start_block);
+		offset = get_unaligned_le16(&ldir->offset);
+		break;
+	default:
+		printf("Error: this is not a directory.\n");
+		return -EINVAL;
+	}
+
+	for (j = 0; j < m_count; j++) {
+		if (m_list[j] == start_block)
+			return (++j * SQFS_METADATA_BLOCK_SIZE) + offset;
+	}
+
+	if (start_block == 0)
+		return offset;
+
+	printf("Error: invalid inode reference to directory table.\n");
+
+	return -EINVAL;
+}
+
+bool sqfs_is_empty_dir(void *dir_i)
+{
+	struct squashfs_base_inode *base = dir_i;
+	struct squashfs_ldir_inode *ldir;
+	struct squashfs_dir_inode *dir;
+	u32 file_size;
+
+	switch (get_unaligned_le16(&base->inode_type)) {
+	case SQFS_DIR_TYPE:
+		dir = (struct squashfs_dir_inode *)base;
+		file_size = get_unaligned_le16(&dir->file_size);
+		break;
+	case SQFS_LDIR_TYPE:
+		ldir = (struct squashfs_ldir_inode *)base;
+		file_size = get_unaligned_le16(&ldir->file_size);
+		break;
+	default:
+		printf("Error: this is not a directory.\n");
+		return false;
+	}
+
+	return file_size == SQFS_EMPTY_FILE_SIZE;
+}

fs/squashfs/sqfs_filesystem.h

@@ -0,0 +1,300 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 Bootlin
+ *
+ * Author: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
+ */
+
+#ifndef SQFS_FILESYSTEM_H
+#define SQFS_FILESYSTEM_H
+
+#include <asm/unaligned.h>
+#include <stdint.h>
+#include <fs.h>
+
+#define SQFS_UNCOMPRESSED_DATA 0x0002
+#define SQFS_MAGIC_NUMBER 0x73717368
+/* The three first members of squashfs_dir_index make a total of 12 bytes */
+#define SQFS_DIR_INDEX_BASE_LENGTH 12
+/* size of metadata (inode and directory) blocks */
+#define SQFS_METADATA_BLOCK_SIZE 8192
+/* Max. number of fragment entries in a metadata block is 512 */
+#define SQFS_MAX_ENTRIES 512
+/* Metadata blocks start by a 2-byte length header */
+#define SQFS_HEADER_SIZE 2
+#define SQFS_LREG_INODE_MIN_SIZE 56
+#define SQFS_DIR_HEADER_SIZE 12
+#define SQFS_MISC_ENTRY_TYPE -1
+#define SQFS_EMPTY_FILE_SIZE 3
+#define SQFS_STOP_READDIR 1
+#define SQFS_EMPTY_DIR -1
+/*
+ * A directory entry object has a fixed length of 8 bytes, corresponding to its
+ * first four members, plus the size of the entry name, which is equal to
+ * 'entry_name' + 1 bytes.
+ */
+#define SQFS_ENTRY_BASE_LENGTH 8
+/* Inode types */
+#define SQFS_DIR_TYPE 1
+#define SQFS_REG_TYPE 2
+#define SQFS_SYMLINK_TYPE 3
+#define SQFS_BLKDEV_TYPE 4
+#define SQFS_CHRDEV_TYPE 5
+#define SQFS_FIFO_TYPE 6
+#define SQFS_SOCKET_TYPE 7
+#define SQFS_LDIR_TYPE 8
+#define SQFS_LREG_TYPE 9
+#define SQFS_LSYMLINK_TYPE 10
+#define SQFS_LBLKDEV_TYPE 11
+#define SQFS_LCHRDEV_TYPE 12
+#define SQFS_LFIFO_TYPE 13
+#define SQFS_LSOCKET_TYPE 14
+
+struct squashfs_super_block {
+	__le32 s_magic;
+	__le32 inodes;
+	__le32 mkfs_time;
+	__le32 block_size;
+	__le32 fragments;
+	__le16 compression;
+	__le16 block_log;
+	__le16 flags;
+	__le16 no_ids;
+	__le16 s_major;
+	__le16 s_minor;
+	__le64 root_inode;
+	__le64 bytes_used;
+	__le64 id_table_start;
+	__le64 xattr_id_table_start;
+	__le64 inode_table_start;
+	__le64 directory_table_start;
+	__le64 fragment_table_start;
+	__le64 export_table_start;
+};
+
+struct squashfs_directory_index {
+	u32 index;
+	u32 start;
+	u32 size;
+	char name[0];
+};
+
+struct squashfs_base_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+};
+
+struct squashfs_ipc_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+	__le32 nlink;
+};
+
+struct squashfs_lipc_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+	__le32 nlink;
+	__le32 xattr;
+};
+
+struct squashfs_dev_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+	__le32 nlink;
+	__le32 rdev;
+};
+
+struct squashfs_ldev_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+	__le32 nlink;
+	__le32 rdev;
+	__le32 xattr;
+};
+
+struct squashfs_symlink_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+	__le32 nlink;
+	__le32 symlink_size;
+	char symlink[0];
+};
+
+struct squashfs_reg_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+	__le32 start_block;
+	__le32 fragment;
+	__le32 offset;
+	__le32 file_size;
+	__le32 block_list[0];
+};
+
+struct squashfs_lreg_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+	__le64 start_block;
+	__le64 file_size;
+	__le64 sparse;
+	__le32 nlink;
+	__le32 fragment;
+	__le32 offset;
+	__le32 xattr;
+	__le32 block_list[0];
+};
+
+struct squashfs_dir_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+	__le32 start_block;
+	__le32 nlink;
+	__le16 file_size;
+	__le16 offset;
+	__le32 parent_inode;
+};
+
+struct squashfs_ldir_inode {
+	__le16 inode_type;
+	__le16 mode;
+	__le16 uid;
+	__le16 guid;
+	__le32 mtime;
+	__le32 inode_number;
+	__le32 nlink;
+	__le32 file_size;
+	__le32 start_block;
+	__le32 parent_inode;
+	__le16 i_count;
+	__le16 offset;
+	__le32 xattr;
+	struct squashfs_directory_index index[0];
+};
+
+union squashfs_inode {
+	struct squashfs_base_inode *base;
+	struct squashfs_dev_inode *dev;
+	struct squashfs_ldev_inode *ldev;
+	struct squashfs_symlink_inode *symlink;
+	struct squashfs_reg_inode *reg;
+	struct squashfs_lreg_inode *lreg;
+	struct squashfs_dir_inode *dir;
+	struct squashfs_ldir_inode *ldir;
+	struct squashfs_ipc_inode *ipc;
+	struct squashfs_lipc_inode *lipc;
+};
+
+struct squashfs_directory_entry {
+	u16 offset;
+	u16 inode_offset;
+	u16 type;
+	u16 name_size;
+	char name[0];
+};
+
+struct squashfs_directory_header {
+	u32 count;
+	u32 start;
+	u32 inode_number;
+};
+
+struct squashfs_fragment_block_entry {
+	u64 start;
+	u32 size;
+	u32 _unused;
+};
+
+struct squashfs_dir_stream {
+	struct fs_dir_stream fs_dirs;
+	struct fs_dirent dentp;
+	/*
+	 * 'size' is the uncompressed size of the entire listing, including
+	 * headers. 'entry_count' is the number of entries following a
+	 * specific header. Both variables are decremented in sqfs_readdir() so
+	 * the function knows when the end of the directory is reached.
+	 */
+	size_t size;
+	int entry_count;
+	/* SquashFS structures */
+	struct squashfs_directory_header *dir_header;
+	struct squashfs_directory_entry *entry;
+	/*
+	 * 'table' points to a position into the directory table. Both 'table'
+	 * and 'inode' are defined for the first time in sqfs_opendir().
+	 * 'table's value changes in sqfs_readdir().
+	 */
+	unsigned char *table;
+	union squashfs_inode i;
+	struct squashfs_dir_inode i_dir;
+	struct squashfs_ldir_inode i_ldir;
+	/*
+	 * References to the tables' beginnings. They are assigned in
+	 * sqfs_opendir() and freed in sqfs_closedir().
+	 */
+	unsigned char *inode_table;
+	unsigned char *dir_table;
+};
+
+struct squashfs_file_info {
+	/* File size in bytes (uncompressed) */
+	size_t size;
+	/* Reference to list of data blocks's sizes */
+	u32 *blk_sizes;
+	/* Offset into the fragment block */
+	u32 offset;
+	/* Offset in which the data blocks begin */
+	u64 start;
+	/* Is file fragmented? */
+	bool frag;
+	/* Compressed fragment */
+	bool comp;
+};
+
+void *sqfs_find_inode(void *inode_table, int inode_number, __le32 inode_count,
+		      __le32 block_size);
+
+int sqfs_dir_offset(void *dir_i, u32 *m_list, int m_count);
+
+int sqfs_read_metablock(unsigned char *file_mapping, int offset,
+			bool *compressed, u32 *data_size);
+
+bool sqfs_is_empty_dir(void *dir_i);
+
+bool sqfs_is_dir(u16 type);
+
+#endif /* SQFS_FILESYSTEM_H */

fs/squashfs/sqfs_inode.c

@@ -0,0 +1,155 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Bootlin
+ *
+ * Author: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
+ */
+
+#include <asm/unaligned.h>
+#include <errno.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "sqfs_decompressor.h"
+#include "sqfs_filesystem.h"
+#include "sqfs_utils.h"
+
+int sqfs_inode_size(struct squashfs_base_inode *inode, u32 blk_size)
+{
+	switch (get_unaligned_le16(&inode->inode_type)) {
+	case SQFS_DIR_TYPE:
+		return sizeof(struct squashfs_dir_inode);
+
+	case SQFS_REG_TYPE: {
+		struct squashfs_reg_inode *reg =
+			(struct squashfs_reg_inode *)inode;
+		u32 fragment = get_unaligned_le32(&reg->fragment);
+		u32 file_size = get_unaligned_le32(&reg->file_size);
+		unsigned int blk_list_size;
+
+		if (SQFS_IS_FRAGMENTED(fragment))
+			blk_list_size = file_size / blk_size;
+		else
+			blk_list_size = DIV_ROUND_UP(file_size, blk_size);
+
+		return sizeof(*reg) + blk_list_size * sizeof(u32);
+	}
+
+	case SQFS_LDIR_TYPE: {
+		struct squashfs_ldir_inode *ldir =
+			(struct squashfs_ldir_inode *)inode;
+		u16 i_count = get_unaligned_le16(&ldir->i_count);
+		unsigned int index_list_size = 0, l = 0;
+		struct squashfs_directory_index *di;
+		u32 sz;
+
+		if (i_count == 0)
+			return sizeof(*ldir);
+
+		di = ldir->index;
+		while (l < i_count + 1) {
+			sz = get_unaligned_le32(&di->size) + 1;
+			index_list_size += sz;
+			di = (void *)di + sizeof(*di) + sz;
+			l++;
+		}
+
+		return sizeof(*ldir) + index_list_size +
+			(i_count + 1) * SQFS_DIR_INDEX_BASE_LENGTH;
+	}
+
+	case SQFS_LREG_TYPE: {
+		struct squashfs_lreg_inode *lreg =
+			(struct squashfs_lreg_inode *)inode;
+		u32 fragment = get_unaligned_le32(&lreg->fragment);
+		u64 file_size = get_unaligned_le64(&lreg->file_size);
+		unsigned int blk_list_size;
+
+		if (fragment == 0xFFFFFFFF)
+			blk_list_size = DIV_ROUND_UP(file_size, blk_size);
+		else
+			blk_list_size = file_size / blk_size;
+
+		return sizeof(*lreg) + blk_list_size * sizeof(u32);
+	}
+
+	case SQFS_SYMLINK_TYPE:
+	case SQFS_LSYMLINK_TYPE: {
+		struct squashfs_symlink_inode *symlink =
+			(struct squashfs_symlink_inode *)inode;
+
+		return sizeof(*symlink) +
+			get_unaligned_le32(&symlink->symlink_size);
+	}
+
+	case SQFS_BLKDEV_TYPE:
+	case SQFS_CHRDEV_TYPE:
+		return sizeof(struct squashfs_dev_inode);
+	case SQFS_LBLKDEV_TYPE:
+	case SQFS_LCHRDEV_TYPE:
+		return sizeof(struct squashfs_ldev_inode);
+	case SQFS_FIFO_TYPE:
+	case SQFS_SOCKET_TYPE:
+		return sizeof(struct squashfs_ipc_inode);
+	case SQFS_LFIFO_TYPE:
+	case SQFS_LSOCKET_TYPE:
+		return sizeof(struct squashfs_lipc_inode);
+	default:
+		printf("Error while searching inode: unknown type.\n");
+		return -EINVAL;
+	}
+}
+
+/*
+ * Given the uncompressed inode table, the inode to be found and the number of
+ * inodes in the table, return inode position in case of success.
+ */
+void *sqfs_find_inode(void *inode_table, int inode_number, __le32 inode_count,
+		      __le32 block_size)
+{
+	struct squashfs_base_inode *base;
+	unsigned int offset = 0, k;
+	int sz;
+
+	if (!inode_table) {
+		printf("%s: Invalid pointer to inode table.\n", __func__);
+		return NULL;
+	}
+
+	for (k = 0; k < le32_to_cpu(inode_count); k++) {
+		base = inode_table + offset;
+		if (get_unaligned_le32(&base->inode_number) == inode_number)
+			return inode_table + offset;
+
+		sz = sqfs_inode_size(base, le32_to_cpu(block_size));
+		if (sz < 0)
+			return NULL;
+
+		offset += sz;
+	}
+
+	printf("Inode not found.\n");
+
+	return NULL;
+}
+
+int sqfs_read_metablock(unsigned char *file_mapping, int offset,
+			bool *compressed, u32 *data_size)
+{
+	unsigned char *data;
+	u16 header;
+
+	data = file_mapping + offset;
+	header = get_unaligned((u16 *)data);
+	*compressed = SQFS_COMPRESSED_METADATA(header);
+	*data_size = SQFS_METADATA_SIZE(header);
+
+	if (*data_size > SQFS_METADATA_BLOCK_SIZE) {
+		printf("Invalid metatada block size: %d bytes.\n", *data_size);
+		return -EINVAL;
+	}
+
+	return 0;
+}

fs/squashfs/sqfs_utils.h

@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 Bootlin
+ *
+ * Author: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
+ */
+
+#ifndef SQFS_UTILS_H
+#define SQFS_UTILS_H
+
+#include <linux/bitops.h>
+#include <linux/kernel.h>
+#include <stdbool.h>
+
+#define SQFS_FRAGMENT_INDEX_OFFSET(A) ((A) % SQFS_MAX_ENTRIES)
+#define SQFS_FRAGMENT_INDEX(A) ((A) / SQFS_MAX_ENTRIES)
+#define SQFS_BLOCK_SIZE(A) ((A) & GENMASK(23, 0))
+#define SQFS_CHECK_FLAG(flag, bit) (((flag) >> (bit)) & 1)
+/* Useful for both fragment and data blocks */
+#define SQFS_COMPRESSED_BLOCK(A) (!((A) & BIT(24)))
+/* SQFS_COMPRESSED_DATA strictly used with super block's 'flags' member */
+#define SQFS_COMPRESSED_DATA(A) (!((A) & 0x0002))
+#define SQFS_IS_FRAGMENTED(A) ((A) != 0xFFFFFFFF)
+/*
+ * These two macros work as getters for a metada block header, retrieving the
+ * data size and if it is compressed/uncompressed
+ */
+#define SQFS_COMPRESSED_METADATA(A) (!((A) & BIT(15)))
+#define SQFS_METADATA_SIZE(A) ((A) & GENMASK(14, 0))
+
+struct squashfs_super_block_flags {
+	/* check: unused
+	 * uncompressed_ids: not supported
+	 */
+	bool uncompressed_inodes;
+	bool uncompressed_data;
+	bool check;
+	bool uncompressed_frags;
+	bool no_frags;
+	bool always_frags;
+	bool duplicates;
+	bool exportable;
+	bool uncompressed_xattrs;
+	bool no_xattrs;
+	bool compressor_options;
+	bool uncompressed_ids;
+};
+
+#endif /* SQFS_UTILS_H  */

include/fs.h

@@ -15,6 +15,7 @@ struct cmd_tbl;
 #define FS_TYPE_SANDBOX	3
 #define FS_TYPE_UBIFS	4
 #define FS_TYPE_BTRFS	5
+#define FS_TYPE_SQUASHFS 6
 
 struct blk_desc;
 

include/squashfs.h

@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 Bootlin
+ *
+ * Author: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
+ *
+ * squashfs.h: SquashFS filesystem implementation.
+ */
+
+#ifndef _SQFS_H_
+#define _SQFS_H_
+
+struct disk_partition;
+
+int sqfs_opendir(const char *filename, struct fs_dir_stream **dirsp);
+int sqfs_readdir(struct fs_dir_stream *dirs, struct fs_dirent **dentp);
+int sqfs_probe(struct blk_desc *fs_dev_desc,
+	       struct disk_partition *fs_partition);
+int sqfs_read(const char *filename, void *buf, loff_t offset,
+	      loff_t len, loff_t *actread);
+int sqfs_size(const char *filename, loff_t *size);
+void sqfs_close(void);
+void sqfs_closedir(struct fs_dir_stream *dirs);
+
+#endif /* SQFS_H  */