From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [EXT4 set 4][PATCH 3/5] i_version:ext4 inode version read/store
Date: Tue, 10 Jul 2007 16:31:17 -0700
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On Sun, 01 Jul 2007 03:37:36 -0400
Mingming Cao <cmm@us.ibm.com> wrote:

> This patch adds 64-bit inode version support to ext4. The lower 32 bits
> are stored in the osd1.linux1.l_i_version field while the high 32 bits
> are stored in the i_version_hi field newly created in the ext4_inode.

So reading the code here does serve to answer the question I raised against
the earlier patch.  A bit.

I'd have thought that this patch and the one which adds i_version_hi should
be folded into a single diff?

> 
> Index: linux-2.6.21/fs/ext4/inode.c
> ===================================================================
> --- linux-2.6.21.orig/fs/ext4/inode.c
> +++ linux-2.6.21/fs/ext4/inode.c
> @@ -2709,6 +2709,13 @@ void ext4_read_inode(struct inode * inod
>  	EXT4_INODE_GET_XTIME(i_atime, inode, raw_inode);
>  	EXT4_EINODE_GET_XTIME(i_crtime, ei, raw_inode);
> 
> +	inode->i_version = le32_to_cpu(raw_inode->i_disk_version);
> +	if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
> +		if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
> +			inode->i_version |=
> +			(__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;

<checks the precedence of "(type)" versus "<<">

<OK>

> +	}

I don't quite see how the above two tests are sufficient to unambiguously
determine that the i_version_hi field is present on-disk.

I guess we're implicitly assuming that if the on-disk inode is big enough
then it _must_ have i_version_hi in there?  If so, why is the comparison
with EXT4_GOOD_OLD_INODE_SIZE needed?

Some description of the overall approach to inode version identification
would be helpful here.

>  	if (S_ISREG(inode->i_mode)) {
>  		inode->i_op = &ext4_file_inode_operations;
>  		inode->i_fop = &ext4_file_operations;
> @@ -2852,8 +2859,14 @@ static int ext4_do_update_inode(handle_t
>  	} else for (block = 0; block < EXT4_N_BLOCKS; block++)
>  		raw_inode->i_block[block] = ei->i_data[block];
> 
> -	if (ei->i_extra_isize)
> +	raw_inode->i_disk_version = cpu_to_le32(inode->i_version);
> +	if (ei->i_extra_isize) {
> +		if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi)) {

There's no comparison with EXT4_GOOD_OLD_INODE_SIZE here...

> +			raw_inode->i_version_hi =
> +				cpu_to_le32(inode->i_version >> 32);
> +		}
>  		raw_inode->i_extra_isize = cpu_to_le16(ei->i_extra_isize);
> +	}
>