The SquashFS super block, located at the beginning of the file system to describe the layout of the filesystem. More...

#include <super.h>

Collaboration diagram for sqfs_super_t:

Public Member Functions
SQFS_API int	sqfs_super_init (sqfs_super_t *super, size_t block_size, sqfs_u32 mtime, SQFS_COMPRESSOR compressor)
	Initialize the SquashFS super block.

SQFS_API int	sqfs_super_write (const sqfs_super_t super, sqfs_file_t file)
	Encode and write a SquashFS super block to disk.

SQFS_API int	sqfs_super_read (sqfs_super_t super, sqfs_file_t file)
	Read a SquashFS super block from disk, decode it and check the fields.

Data Fields
sqfs_u32	magic
	Magic number. Must be set to SQFS_MAGIC.

sqfs_u32	inode_count
	Total number of inodes.

sqfs_u32	modification_time
	Last time the filesystem was modified.

sqfs_u32	block_size
	The data block size in bytes.

sqfs_u32	fragment_entry_count
	The number of fragment blocks in the data area.

sqfs_u16	compression_id
	Identifies the compressor that has been used.

sqfs_u16	block_log
	The log2 of the block_size field for sanity checking.

sqfs_u16	flags
	A combination of SQFS_SUPER_FLAGS flags.

sqfs_u16	id_count
	The total number of unique user or group IDs.

sqfs_u16	version_major
	Must be SQFS_VERSION_MAJOR.

sqfs_u16	version_minor
	Must be SQFS_VERSION_MINOR.

sqfs_u64	root_inode_ref
	A reference to the root inode.

sqfs_u64	bytes_used
	Total size of the file system in bytes, not counting padding.

sqfs_u64	id_table_start
	On-disk location of the ID table.

sqfs_u64	xattr_id_table_start
	On-disk location of the extended attribute table (if present)

sqfs_u64	inode_table_start
	On-disk location of the first meta data block containing the inodes.

sqfs_u64	directory_table_start
	On-disk location of the first meta data block containing the directory entries.

sqfs_u64	fragment_table_start
	On-disk location of the fragment table (if present)

sqfs_u64	export_table_start
	On-disk location of the export table (if present)

Detailed Description

The SquashFS super block, located at the beginning of the file system to describe the layout of the filesystem.

Examples: list_files.c.

Definition at line 47 of file super.h.

Member Function Documentation

◆ sqfs_super_init()

SQFS_API int sqfs_super_init	(	sqfs_super_t *	super,
		size_t	block_size,
		sqfs_u32	mtime,
		SQFS_COMPRESSOR	compressor
	)

Initialize the SquashFS super block.

Parameters

super	A pointer to a super block structure.
block_size	The uncompressed size of the data blocks in bytes.
mtime	The modification time stamp to set.
compressor	The compressor ID to set.

Returns: Zero on success, an SQFS_ERROR value if one of the fields does not hold a valid value.

◆ sqfs_super_read()

SQFS_API int sqfs_super_read	(	sqfs_super_t *	super,
		sqfs_file_t *	file
	)

Read a SquashFS super block from disk, decode it and check the fields.

Parameters

super	A pointer to the super block structure to fill.
file	A file object through which to access the filesystem image.

Returns: Zero on success, an SQFS_ERROR value if one of the fields does not hold a valid value.

◆ sqfs_super_write()

SQFS_API int sqfs_super_write	(	const sqfs_super_t *	super,
		sqfs_file_t *	file
	)

Encode and write a SquashFS super block to disk.

Parameters

super	A pointer to the super block structure to write.
file	A file object through which to access the filesystem image.

Returns: Zero on success, an SQFS_ERROR value if one of the fields does not hold a valid value.

Field Documentation

◆ block_log

sqfs_u16 block_log

The log2 of the block_size field for sanity checking.

Must be no less than 12 and not larger than 20.

Definition at line 91 of file super.h.

◆ block_size

sqfs_u32 block_size

The data block size in bytes.

Must be a power of 2, no less than 4k and not larger than 1M.

Examples: list_files.c.

Definition at line 72 of file super.h.

◆ bytes_used

sqfs_u64 bytes_used

Total size of the file system in bytes, not counting padding.

Definition at line 127 of file super.h.

◆ compression_id

sqfs_u16 compression_id

Identifies the compressor that has been used.

Valid identifiers are in the SQFS_COMPRESSOR enum.

Examples: list_files.c.

Definition at line 84 of file super.h.

◆ directory_table_start

sqfs_u64 directory_table_start

On-disk location of the first meta data block containing the directory entries.

This value must point to a location after the inode table but before the fragment, export, ID and xattr tables.

Definition at line 164 of file super.h.

◆ export_table_start

sqfs_u64 export_table_start

On-disk location of the export table (if present)

This value must either point to a location after directory table (and if present after the fragment table), but before the ID table, or it must be set to 0xFFFFFFFF to indicate that the table is not present.

Definition at line 183 of file super.h.

◆ flags

sqfs_u16 flags

A combination of SQFS_SUPER_FLAGS flags.

Most of the flags that can be set here are informative only.

Definition at line 98 of file super.h.

◆ fragment_entry_count

sqfs_u32 fragment_entry_count

The number of fragment blocks in the data area.

Definition at line 77 of file super.h.

◆ fragment_table_start

sqfs_u64 fragment_table_start

On-disk location of the fragment table (if present)

This value must either point to a location after the directory table, but before the export, ID and xattr tables, or it must be set to 0xFFFFFFFF to indicate that the table is not present.

Definition at line 173 of file super.h.

◆ id_count

sqfs_u16 id_count

The total number of unique user or group IDs.

Definition at line 103 of file super.h.

◆ id_table_start

sqfs_u64 id_table_start

On-disk location of the ID table.

This value must point to a location after the directory table and (if present) after the export and fragment tables, but before the xattr table.

Definition at line 136 of file super.h.

◆ inode_count

sqfs_u32 inode_count

Total number of inodes.

Definition at line 56 of file super.h.

◆ inode_table_start

sqfs_u64 inode_table_start

On-disk location of the first meta data block containing the inodes.

This value must point to a location before the directory table.

Definition at line 155 of file super.h.

◆ magic

sqfs_u32 magic

Magic number. Must be set to SQFS_MAGIC.

Definition at line 51 of file super.h.

◆ modification_time

sqfs_u32 modification_time

Last time the filesystem was modified.

This field counts seconds (not counting leap seconds) since 00:00, Jan 1 1970 UTC. This field is unsigned, so it expires in the year 2106 (as opposed to 2038).

Definition at line 65 of file super.h.

◆ root_inode_ref

sqfs_u64 root_inode_ref

A reference to the root inode.

The bits 16 to 48 hold an offset that is added to inode_table_start to get the location of the meta data block containing the inode. The lower 16 bits hold a byte offset into the uncompressed block.

Definition at line 122 of file super.h.

◆ version_major

sqfs_u16 version_major

Must be SQFS_VERSION_MAJOR.

Definition at line 108 of file super.h.

◆ version_minor

sqfs_u16 version_minor

Must be SQFS_VERSION_MINOR.

Definition at line 113 of file super.h.

◆ xattr_id_table_start

sqfs_u64 xattr_id_table_start

On-disk location of the extended attribute table (if present)

See sqfs_xattr_reader_t for an overview on how SquashFS stores extended attributes on disk.

This value must either point to a location after the ID table, or it must be set to 0xFFFFFFFF to indicate the table is not present.

Definition at line 147 of file super.h.

The documentation for this struct was generated from the following file:

include/sqfs/super.h

Public Member Functions

Data Fields

Detailed Description

Member Function Documentation

◆ sqfs_super_init()

◆ sqfs_super_read()

◆ sqfs_super_write()

Field Documentation

◆ block_log

◆ block_size

◆ bytes_used

◆ compression_id

◆ directory_table_start

◆ export_table_start

◆ flags

◆ fragment_entry_count

◆ fragment_table_start

◆ id_count

◆ id_table_start

◆ inode_count

◆ inode_table_start

◆ magic

◆ modification_time

◆ root_inode_ref

◆ version_major

◆ version_minor

◆ xattr_id_table_start