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SubjectRe: [PATCH 02/16] f2fs: add on-disk layout
On Fri, Oct 05, 2012 at 08:56:44PM +0900, ????????? wrote:
> +struct node_footer {
> + __le32 nid; /* node id */
> + __le32 ino; /* inode nunmber */
> + __le32 cold:1; /* cold mark */
> + __le32 fsync:1; /* fsync mark */
> + __le32 dentry:1; /* dentry mark */
> + __le32 offset:29; /* offset in inode's node space */

A bitfield for a on-disk structure? This will have endianity issues,
(but I don't know if you intend to support big-endian). It's not enough
to use cpu_to_le* as in

fill_node_footer(...) {

rn->footer.offset = cpu_to_le32(ofs);

}

because the bitfield inside the structure will be already defined
reversed. The cpu_to_le macro will only convert value of 'ofs' but will
place it to different bits than it would on a little-endian arch.

There are macros to define bitfields in an endian-neutral way (or do it
by #ifdefs though it also involves duplicating the item names), or you
can alternatively use two structs fr disk-only and memory-only access,
the disk one stores __le32 with value combined of all and the in-memory
gets set up properly and will look like your current version of the
structure.

(More about not using bitfields http://yarchive.net/comp/linux/bitfields.html)

> + __le64 cp_ver; /* checkpoint version */
> + __le32 next_blkaddr; /* next node page block address */
> +} __packed;
> +


david


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