RE: [PATCH 02/16 v2] f2fs: add on-disk layout

[Jaegeuk Kim <jaegeuk.kim@samsung.com>]

> -----Original Message-----
> From: NeilBrown [mailto:neilb@suse.de]
> Sent: Tuesday, October 23, 2012 12:47 PM
> To: Jaegeuk Kim
> Cc: linux-fsdevel@vger.kernel.org; linux-kernel@vger.kernel.org; gregkh@linuxfoundation.org;
> viro@zeniv.linux.org.uk; arnd@arndb.de; tytso@mit.edu; chur.lee@samsung.com; cm224.lee@samsung.com;
> jooyoung.hwang@samsung.com
> Subject: Re: [PATCH 02/16 v2] f2fs: add on-disk layout
> Importance: High
> 
> On Tue, 23 Oct 2012 11:26:00 +0900 Jaegeuk Kim <jaegeuk.kim@samsung.com>
> wrote:
> 
> > This adds a header file describing the on-disk layout of f2fs.
> >
> 
> 
> > +struct f2fs_inode {
> > +	__le16 i_mode;			/* File mode */
> > +	__u8 i_advise;			/* File hints */
> > +	__u8 i_reserved;		/* Reserved */
> > +	__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_ctime;			/* Inode change time */
> > +	__le64 i_mtime;			/* Modification time */
> > +	__le32 i_ctime_nsec;
> > +	__le32 i_mtime_nsec;
> > +	__le32 current_depth;
> > +	__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_MAX_NAME_LEN];	/* file name for SPOR */
> > +
> > +	struct f2fs_extent i_ext;	/* caching a largest extent */
> > +
> > +	__le32 i_addr[ADDRS_PER_INODE];	/* Pointers to data blocks */
> > +
> > +	__le32 i_nid[5];		/* direct(2), indirect(2),
> > +						double_indirect(1) node id */
> > +} __packed;
> > +
> 
> 
> You appear to have dropped i_btime - no big deal, you weren't using it anyway.
> However if you ever want to support NFS export you will need some value which
> is assigned when the inode is allocated and never changed until it is
> de-allocated.  This is used to detect when an NFS file-handle refers to a
> previous incarnation of an inode and so should be rejected as STALE.
> i_btime could have possibly provided this, but not any more.  You might want
> to add something back.
> ext3 uses "i_generation" and has an 's_next_generation' in the superblock to
> ensure that each new inode gets a new generation number.

Agreed. I'll check that.

> 
> You've also dropped i_atime.  I can certainly understand the desire to do
> that, but I wonder if it is entirely wise.  There are some use-cases where
> i_mtime is a poor substitute.

Got it.

> 
> Also 'current_depth' looks a little odd without a 'i_' prefix.  It wouldn't
> hurt to have a comment noting that it is for directories.

Agreed.
Thank you for comments. :)

> 
> Thanks,
> NeilBrown


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Jaegeuk Kim
Samsung