Messages in this thread | | | Date | Sun, 7 Oct 2012 00:21:05 +0200 | From | David Sterba <> | Subject | Re: [PATCH 02/16] f2fs: add on-disk layout |
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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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