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Date:   Wed, 14 Mar 2018 21:54:01 -0700
From:   "Darrick J. Wong" <darrick.wong@oracle.com>
To:     Andiry Xu <jix024@eng.ucsd.edu>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nvdimm@lists.01.org, dan.j.williams@intel.com,
        andy.rudoff@intel.com, coughlan@redhat.com, swanson@cs.ucsd.edu,
        david@fromorbit.com, jack@suse.com, swhiteho@redhat.com,
        miklos@szeredi.hu, andiry.xu@gmail.com,
        Andiry Xu <jix024@cs.ucsd.edu>
Subject: Re: [RFC v2 03/83] Add super.h.
Message-ID: <20180315045401.GB4860@magnolia>
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On Sat, Mar 10, 2018 at 10:17:44AM -0800, Andiry Xu wrote:
> From: Andiry Xu <jix024@cs.ucsd.edu>
> 
> This header file defines NOVA persistent and volatile superblock
> data structures.
> 
> It also defines NOVA block layout:
> 
> Page 0: Superblock
> Page 1: Reserved inodes
> Page 2 - 15: Reserved
> Page 16 - 31: Inode table pointers
> Page 32 - 47: Journal address pointers
> Page 48 - 63: Reserved
> Pages n-2: Replicate reserved inodes
> Pages n-1: Replicate superblock
> 
> Other pages are for normal inodes, logs and data.
> 
> Signed-off-by: Andiry Xu <jix024@cs.ucsd.edu>
> ---
>  fs/nova/super.h | 149 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 149 insertions(+)
>  create mode 100644 fs/nova/super.h
> 
> diff --git a/fs/nova/super.h b/fs/nova/super.h
> new file mode 100644
> index 0000000..cb53908
> --- /dev/null
> +++ b/fs/nova/super.h
> @@ -0,0 +1,149 @@
> +#ifndef __SUPER_H
> +#define __SUPER_H
> +/*
> + * Structure of the NOVA super block in PMEM
> + *
> + * The fields are partitioned into static and dynamic fields. The static fields
> + * never change after file system creation. This was primarily done because
> + * nova_get_block() returns NULL if the block offset is 0 (helps in catching
> + * bugs). So if we modify any field using journaling (for consistency), we
> + * will have to modify s_sum which is at offset 0. So journaling code fails.
> + * This (static+dynamic fields) is a temporary solution and can be avoided
> + * once the file system becomes stable and nova_get_block() returns correct
> + * pointers even for offset 0.
> + */
> +struct nova_super_block {
> +	/* static fields. they never change after file system creation.
> +	 * checksum only validates up to s_start_dynamic field below
> +	 */
> +	__le32		s_sum;			/* checksum of this sb */
> +	__le32		s_magic;		/* magic signature */
> +	__le32		s_padding32;
> +	__le32		s_blocksize;		/* blocksize in bytes */
> +	__le64		s_size;			/* total size of fs in bytes */
> +	char		s_volume_name[16];	/* volume name */
> +
> +	/* all the dynamic fields should go here */
> +	__le64		s_epoch_id;		/* Epoch ID */
> +
> +	/* s_mtime and s_wtime should be together and their order should not be
> +	 * changed. we use an 8 byte write to update both of them atomically
> +	 */
> +	__le32		s_mtime;		/* mount time */
> +	__le32		s_wtime;		/* write time */

Hmmm, 32-bit timestamps?  2038 isn't that far away...

> +} __attribute((__packed__));
> +
> +#define NOVA_SB_SIZE 512       /* must be power of two */
> +
> +/* ======================= Reserved blocks ========================= */
> +
> +/*
> + * Page 0 contains super blocks;
> + * Page 1 contains reserved inodes;
> + * Page 2 - 15 are reserved.
> + * Page 16 - 31 contain pointers to inode tables.
> + * Page 32 - 47 contain pointers to journal pages.
> + */
> +#define	HEAD_RESERVED_BLOCKS	64
> +#define	NUM_JOURNAL_PAGES	16
> +
> +#define	SUPER_BLOCK_START       0 // Superblock
> +#define	RESERVE_INODE_START	1 // Reserved inodes
> +#define	INODE_TABLE_START	16 // inode table pointers
> +#define	JOURNAL_START		32 // journal pointer table
> +
> +/* For replica super block and replica reserved inodes */
> +#define	TAIL_RESERVED_BLOCKS	2
> +
> +/* ======================= Reserved inodes ========================= */
> +
> +/* We have space for 31 reserved inodes */
> +#define NOVA_ROOT_INO		(1)
> +#define NOVA_INODETABLE_INO	(2)	/* Fake inode associated with inode
> +					 * stroage.  We need this because our
> +					 * allocator requires inode to be
> +					 * associated with each allocation.
> +					 * The data actually lives in linked
> +					 * lists in INODE_TABLE_START. */
> +#define NOVA_BLOCKNODE_INO	(3)     /* Storage for allocator state */
> +#define NOVA_LITEJOURNAL_INO	(4)     /* Storage for lightweight journals */
> +#define NOVA_INODELIST_INO	(5)     /* Storage for Inode free list */
> +
> +
> +/* Normal inode starts at 32 */
> +#define NOVA_NORMAL_INODE_START      (32)

I've been wondering this whole time, why not make the inode number the
byte offset into the pmem?  Then you don't have to lose the last 8 bytes
of each inode block to point to the next one.

--D

> +
> +
> +
> +/*
> + * NOVA super-block data in DRAM
> + */
> +struct nova_sb_info {
> +	struct super_block *sb;			/* VFS super block */
> +	struct nova_super_block *nova_sb;	/* DRAM copy of SB */
> +	struct block_device *s_bdev;
> +	struct dax_device *s_dax_dev;
> +
> +	/*
> +	 * base physical and virtual address of NOVA (which is also
> +	 * the pointer to the super block)
> +	 */
> +	phys_addr_t	phys_addr;
> +	void		*virt_addr;
> +	void		*replica_reserved_inodes_addr;
> +	void		*replica_sb_addr;
> +
> +	unsigned long	num_blocks;
> +
> +	/* Mount options */
> +	unsigned long	bpi;
> +	unsigned long	blocksize;
> +	unsigned long	initsize;
> +	unsigned long	s_mount_opt;
> +	kuid_t		uid;    /* Mount uid for root directory */
> +	kgid_t		gid;    /* Mount gid for root directory */
> +	umode_t		mode;   /* Mount mode for root directory */
> +	atomic_t	next_generation;
> +	/* inode tracking */
> +	unsigned long	s_inodes_used_count;
> +	unsigned long	head_reserved_blocks;
> +	unsigned long	tail_reserved_blocks;
> +
> +	struct mutex	s_lock;	/* protects the SB's buffer-head */
> +
> +	int cpus;
> +
> +	/* Current epoch. volatile guarantees visibility */
> +	volatile u64 s_epoch_id;
> +
> +	/* ZEROED page for cache page initialized */
> +	void *zeroed_page;
> +};
> +
> +static inline struct nova_sb_info *NOVA_SB(struct super_block *sb)
> +{
> +	return sb->s_fs_info;
> +}
> +
> +static inline struct nova_super_block
> +*nova_get_redund_super(struct super_block *sb)
> +{
> +	struct nova_sb_info *sbi = NOVA_SB(sb);
> +
> +	return (struct nova_super_block *)(sbi->replica_sb_addr);
> +}
> +
> +
> +/* If this is part of a read-modify-write of the super block,
> + * nova_memunlock_super() before calling!
> + */
> +static inline struct nova_super_block *nova_get_super(struct super_block *sb)
> +{
> +	struct nova_sb_info *sbi = NOVA_SB(sb);
> +
> +	return (struct nova_super_block *)sbi->virt_addr;
> +}
> +
> +extern void nova_error_mng(struct super_block *sb, const char *fmt, ...);
> +
> +#endif
> -- 
> 2.7.4
>