f2fs学习笔记 - 4. f2fs文件系统组件说明
宋博易
1. 前言
本文主要是以f2fs文件系统为例来说明文件系统编程模式，要实现一个文件系统，需要实现哪些组件，以及如何被使用的。
2. 文件系统组件说明
2.1 定义文件系统类型（fs/f2fs/super.c）
static struct file_system_type f2fs_fs_type = {
.owner = THIS_MODULE,
.name = "f2fs",
.mount = f2fs_mount,
.kill_sb = kill_block_super,
.fs_flags = FS_REQUIRES_DEV,
};
任何具体的文件系统都需要定义file_system_type 结构体，它最主要的是指定了f2fs_mount的mount回调，通过init_f2fs_fs初始化函数中调用register_filesystem来完成文件系统注册
module_init(init_f2fs_fs)
|--static int __init init_f2fs_fs(void)
|--register_filesystem(&f2fs_fs_type);
2.2 定义超级块结构与操作集（fs/f2fs/super.c）
struct f2fs_super_block {
__le32 magic; /* Magic Number */
__le16 major_ver; /* Major Version */
__le16 minor_ver; /* Minor Version */
__le32 log_sectorsize; /* log2 sector size in bytes */
__le32 log_sectors_per_block; /* log2 # of sectors per block */
__le32 log_blocksize; /* log2 block size in bytes */
__le32 log_blocks_per_seg; /* log2 # of blocks per segment */
__le32 segs_per_sec; /* # of segments per section */
__le32 secs_per_zone; /* # of sections per zone */
__le32 checksum_offset; /* checksum offset inside super block */
__le64 block_count; /* total # of user blocks */
__le32 section_count; /* total # of sections */
__le32 segment_count; /* total # of segments */
__le32 segment_count_ckpt; /* # of segments for checkpoint */
__le32 segment_count_sit; /* # of segments for SIT */
__le32 segment_count_nat; /* # of segments for NAT */
__le32 segment_count_ssa; /* # of segments for SSA */
__le32 segment_count_main; /* # of segments for main area */
__le32 segment0_blkaddr; /* start block address of segment 0 */
__le32 cp_blkaddr; /* start block address of checkpoint */
__le32 sit_blkaddr; /* start block address of SIT */
__le32 nat_blkaddr; /* start block address of NAT */
__le32 ssa_blkaddr; /* start block address of SSA */
__le32 main_blkaddr; /* start block address of main area */
__le32 root_ino; /* root inode number */
__le32 node_ino; /* node inode number */
__le32 meta_ino; /* meta inode number */
__u8 uuid[16]; /* 128-bit uuid for volume */
__le16 volume_name[MAX_VOLUME_NAME]; /* volume name */
__le32 extension_count; /* # of extensions below */
__u8 extension_list[F2FS_MAX_EXTENSION][F2FS_EXTENSION_LEN];/* extension array */
__le32 cp_payload;
__u8 version[VERSION_LEN]; /* the kernel version */
__u8 init_version[VERSION_LEN]; /* the initial kernel version */
__le32 feature; /* defined features */
__u8 encryption_level; /* versioning level for encryption */
__u8 encrypt_pw_salt[16]; /* Salt used for string2key algorithm */
struct f2fs_device devs[MAX_DEVICES]; /* device list */
__le32 qf_ino[F2FS_MAX_QUOTAS]; /* quota inode numbers */
__u8 hot_ext_count; /* # of hot file extension */
__le16 s_encoding; /* Filename charset encoding */
__le16 s_encoding_flags; /* Filename charset encoding flags */
__u8 reserved[306]; /* valid reserved region */
__le32 crc; /* checksum of superblock */
} __packed;
文件系统需要实现super_operations结构体变量，它定义了操作inode相关的一系列回调。
static const struct super_operations f2fs_sops = {
.alloc_inode = f2fs_alloc_inode,
.free_inode = f2fs_free_inode,
.drop_inode = f2fs_drop_inode,
.write_inode = f2fs_write_inode,
.dirty_inode = f2fs_dirty_inode,
.show_options = f2fs_show_options,
#ifdef CONFIG_QUOTA
.quota_read = f2fs_quota_read,
.quota_write = f2fs_quota_write,
.get_dquots = f2fs_get_dquots,
#endif
.evict_inode = f2fs_evict_inode,
.put_super = f2fs_put_super,
.sync_fs = f2fs_sync_fs,
.freeze_fs = f2fs_freeze,
.unfreeze_fs = f2fs_unfreeze,
.statfs = f2fs_statfs,
.remount_fs = f2fs_remount,
};
它主要会在文件系统类型file_system_type的mount回调中使用，用于初始化super_blcok的s_op
static struct dentry *f2fs_mount(struct file_system_type *fs_type, int flags,...,void *data)
|--mount_bdev(fs_type, flags, dev_name, data, f2fs_fill_super);
|--struct super_block *s
| //~~~创建vfs超级块 super_block
|--s = sget(fs_type, test_bdev_super, set_bdev_super, flags | SB_NOSEC, bdev)
|--f2fs_fill_super(s, data, flags & SB_SILENT ? 1 : 0)
|--struct f2fs_sb_info *sbi
|--struct f2fs_super_block *raw_super;
| //~~~创建具体文件系统超级块信息 f2fs_sb_info
|--sbi = kzalloc(sizeof(struct f2fs_sb_info), GFP_KERNEL)
|--read_raw_super_block(sbi, &raw_super, &valid_super_block,...)
| |--struct f2fs_super_block *super
| | //~~~创建具体文件系统超级块 f2fs_super_block
| |--super = kzalloc(sizeof(struct f2fs_super_block), GFP_KERNEL)
| |--*raw_super = super
| //~~~将具体文件系统超级块信息初始化给VFS超级块
|--s->s_fs_info = sbi
//~~~将具体文件系统超级块初始化给具体文件系统超级块信息
sbi->raw_super = raw_super
//~~~将创建的具体文件系统超级块操作函数集 给super_block的s_op
s->s_op = &f2fs_sops
2.3 定义inode结构(include/linux/f2fs_fs.h)
struct f2fs_inode {
__le16 i_mode; /* file mode */
__u8 i_advise; /* file hints */
__u8 i_inline; /* file inline flags */
__le32 i_uid; /* user ID */
__le32 i_gid; /* group ID */
__le32 i_links; /* links count */
__le64 i_size; /* file size in bytes */
__le64 i_blocks; /* file size in blocks */
__le64 i_atime; /* access time */
__le64 i_ctime; /* change time */
__le64 i_mtime; /* modification time */
__le32 i_atime_nsec; /* access time in nano scale */
__le32 i_ctime_nsec; /* change time in nano scale */
__le32 i_mtime_nsec; /* modification time in nano scale */
__le32 i_generation; /* file version (for NFS) */
union {
__le32 i_current_depth; /* only for directory depth */
__le16 i_gc_failures; /*
* # of gc failures on pinned file.
* only for regular files.
*/
};
__le32 i_xattr_nid; /* nid to save xattr */
__le32 i_flags; /* file attributes */
__le32 i_pino; /* parent inode number */
__le32 i_namelen; /* file name length */
__u8 i_name[F2FS_NAME_LEN]; /* file name for SPOR */
__u8 i_dir_level; /* dentry_level for large dir */
struct f2fs_extent i_ext; /* caching a largest extent */
union {
struct {
__le16 i_extra_isize; /* extra inode attribute size */
__le16 i_inline_xattr_size; /* inline xattr size, unit: 4 bytes */
__le32 i_projid; /* project id */
__le32 i_inode_checksum;/* inode meta checksum */
__le64 i_crtime; /* creation time */
__le32 i_crtime_nsec; /* creation time in nano scale */
__le64 i_compr_blocks; /* # of compressed blocks */
__u8 i_compress_algorithm; /* compress algorithm */
__u8 i_log_cluster_size; /* log of cluster size */
__le16 i_padding; /* padding */
__le32 i_extra_end[0]; /* for attribute size calculation */
} __packed;
__le32 i_addr[DEF_ADDRS_PER_INODE]; /* Pointers to data blocks */
};
__le32 i_nid[DEF_NIDS_PER_INODE]; /* direct(2), indirect(2),
double_indirect(1) node id */
} __packed;
2.4 定义inode操作函数集
在f2fs_iget时会初始化inode操作函数集，而在通过inode号来获取inode时均会调用到此函数
- 常规文件的inode操作函数集
# fs/f2fs/file.c
const struct inode_operations f2fs_file_inode_operations = {
.getattr = f2fs_getattr,
.setattr = f2fs_setattr,
.get_acl = f2fs_get_acl,
.set_acl = f2fs_set_acl,
.listxattr = f2fs_listxattr,
.fiemap = f2fs_fiemap,
};
- 目录文件的inode操作函数集
# fs/f2fs/namei.c
const struct inode_operations f2fs_dir_inode_operations = {
.create = f2fs_create,
.lookup = f2fs_lookup,
.link = f2fs_link,
.unlink = f2fs_unlink,
.symlink = f2fs_symlink,
.mkdir = f2fs_mkdir,
.rmdir = f2fs_rmdir,
.mknod = f2fs_mknod,
.rename = f2fs_rename2,
.tmpfile = f2fs_tmpfile,
.getattr = f2fs_getattr,
.setattr = f2fs_setattr,
.get_acl = f2fs_get_acl,
.set_acl = f2fs_set_acl,
.listxattr = f2fs_listxattr,
.fiemap = f2fs_fiemap,
}
- 加密链接的inode操作函数集
const struct inode_operations f2fs_encrypted_symlink_inode_operations = {
.get_link = f2fs_encrypted_get_link,
.getattr = f2fs_getattr,
.setattr = f2fs_setattr,
.listxattr = f2fs_listxattr,
};
- 普通链接的inode操作函数集
const struct inode_operations f2fs_symlink_inode_operations = {
.get_link = f2fs_get_link,
.getattr = f2fs_getattr,
.setattr = f2fs_setattr,
.listxattr = f2fs_listxattr,
};
- 特殊文件（字符设备/块设备/管道文件）的inode操作函数集
const struct inode_operations f2fs_special_inode_operations = {
.getattr = f2fs_getattr,
.setattr = f2fs_setattr,
.get_acl = f2fs_get_acl,
.set_acl = f2fs_set_acl,
.listxattr = f2fs_listxattr,
};
2.5 定义inode文件操作函数集
在f2fs_iget时会初始化inode文件操作函数集，而在通过inode号来获取inode时均会调用到此函数
- 常规文件的inode文件操作函数集
# fs/f2fs/file.c
const struct file_operations f2fs_file_operations = {
.llseek = f2fs_llseek,
.read_iter = f2fs_file_read_iter,
.write_iter = f2fs_file_write_iter,
.open = f2fs_file_open,
.release = f2fs_release_file,
.mmap = f2fs_file_mmap,
.flush = f2fs_file_flush,
.fsync = f2fs_sync_file,
.fallocate = f2fs_fallocate,
.unlocked_ioctl = f2fs_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = f2fs_compat_ioctl,
#endif
.splice_read = generic_file_splice_read,
.splice_write = iter_file_splice_write,
};
- 目录文件的inode文件操作函数集
const struct file_operations f2fs_dir_operations = {
.llseek = generic_file_llseek,
.read = generic_read_dir,
.iterate_shared = f2fs_readdir,
.fsync = f2fs_sync_file,
.open = f2fs_dir_open,
.unlocked_ioctl = f2fs_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = f2fs_compat_ioctl,
#endif
};
- 特殊文件的inode文件操作函数集
字符设备
# fs/char_dev.c
const struct file_operations def_chr_fops = {
.open = chrdev_open,
.llseek = noop_llseek,
}
块设备
# fs/block_dev.c
const struct file_operations def_blk_fops = {
.open = blkdev_open,
.release = blkdev_close,
.llseek = block_llseek,
.read_iter = blkdev_read_iter,
.write_iter = blkdev_write_iter,
.iopoll = blkdev_iopoll,
.mmap = generic_file_mmap,
.fsync = blkdev_fsync,
.unlocked_ioctl = block_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = compat_blkdev_ioctl,
#endif
.splice_read = generic_file_splice_read,
.splice_write = iter_file_splice_write,
.fallocate = blkdev_fallocate,
};
管道设备
# fs/pipe.c
const struct file_operations pipefifo_fops = {
.open = fifo_open,
.llseek = no_llseek,
.read_iter = pipe_read,
.write_iter = pipe_write,
.poll = pipe_poll,
.unlocked_ioctl = pipe_ioctl,
.release = pipe_release,
.fasync = pipe_fasync,
}
2.6 定义inode address_space操作函数集
在f2fs_iget时会初始化inode address_space操作函数集，而在通过inode号来获取inode时均会调用到此函数
- node info的inode address_space操作函数集
# fs/f2fs/node.c
/*
* Structure of the f2fs node operations
*/
const struct address_space_operations f2fs_node_aops = {
.writepage = f2fs_write_node_page,
.writepages = f2fs_write_node_pages,
.set_page_dirty = f2fs_set_node_page_dirty,
.invalidatepage = f2fs_invalidate_page,
.releasepage = f2fs_release_page,
#ifdef CONFIG_MIGRATION
.migratepage = f2fs_migrate_page,
#endif
};
- meta info的inode address_space操作函数集
# fs/f2fs/checkpoint.c
const struct address_space_operations f2fs_meta_aops = {
.writepage = f2fs_write_meta_page,
.writepages = f2fs_write_meta_pages,
.set_page_dirty = f2fs_set_meta_page_dirty,
.invalidatepage = f2fs_invalidate_page,
.releasepage = f2fs_release_page,
#ifdef CONFIG_MIGRATION
.migratepage = f2fs_migrate_page,
#endif
};
- 常规文件的inode address_space操作函数集
# fs/f2fs/data.c
const struct address_space_operations f2fs_dblock_aops = {
.readpage = f2fs_read_data_page,
.readahead = f2fs_readahead,
.writepage = f2fs_write_data_page,
.writepages = f2fs_write_data_pages,
.write_begin = f2fs_write_begin,
.write_end = f2fs_write_end,
.set_page_dirty = f2fs_set_data_page_dirty,
.invalidatepage = f2fs_invalidate_page,
.releasepage = f2fs_release_page,
.direct_IO = f2fs_direct_IO,
.bmap = f2fs_bmap,
.swap_activate = f2fs_swap_activate,
.swap_deactivate = f2fs_swap_deactivate,
#ifdef CONFIG_MIGRATION
.migratepage = f2fs_migrate_page,
#endif
};
- 目录文件的inode address_space操作函数集
# fs/f2fs/data.c
同常规文件
- 链接文件的inode address_space操作函数集
# fs/f2fs/data.c
同常规文件
2.7 定义dentry操作函数集
# f2fs/dir.c
#ifdef CONFIG_UNICODE
const struct dentry_operations f2fs_dentry_ops = {
.d_hash = generic_ci_d_hash,
.d_compare = generic_ci_d_compare,
};
#endif
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