[Yaffs] is the extra info must included in yaffs_ext_tags ?

i'm working with yaffs2 the newest version in git. i have some question
about the one and have some troubles now.
1.the newest version add a new structure "summary_header",why and what's
the benifit?
2.i'm now migrite yaffs to our system in YDI mode.when i read and write
data to/from nand flash i don't use packed tags,but when i try to open a
file,yaffs try to write a new headr to flash,the write is ok,but when the
summary_tag is adding,the member's of summary_tag is a chaos,i found this
occured for the function yaffs_pack_tags2_tags_only() ,in this function
program go to the branch "if (yaffs_check_tags_extra_packable(t)) {" which
makes the value a fault. so i'm wondering if the extra info member in
yaffs_ext_tags is a must member?can i remove it?

thanks for helping me.
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Regards,
Ezio.