Messages in this thread | | | Date | Thu, 29 Jun 2006 15:14:19 -0700 | From | Daniel Phillips <> | Subject | Re: [RFC 1/2] ext3: enlarge blocksize and fix rec_len overflow |
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Andreas Dilger wrote: > On Jun 29, 2006 11:10 -0700, Daniel Phillips wrote: >>Andreas Dilger wrote: >>>On Jun 28, 2006 17:50 +0200, Johann Lombardi wrote: >>> >>>>ext2/ext3_dir_entry_2 has a 16-bit entry(rec_len) and it would overflow >>>>with 64KB blocksize. This patch prevent from overflow by limiting >>>>rec_len to 65532. >>> >>>Having a max rec_len of 65532 is rather unfortunate, since the dir >>>blocks always need to filled with dir entries. 65536 - 65532 = 4, and >>>the minimum ext3_dir_entry size is 8 bytes. I would instead make this >>>maybe 64 bytes less so that there is room for a filename in the "tail" >>>dir_entry. >> >>Then why not introduce a little symmetry by making max rec_len 2**15 and >>treat big directory blocks as an array of smaller ones? I dimly recall >>the page-cache oriented Ext2 dir code already does this. > > I have no objection to this at all, but I think it will lead to a slightly > more complex implementation. We even discussed in the distant past to > make large directories a series of 4kB "chunks", for fs blocksize >= 4kB. > This has negative implications for large filenames because the internal > free space fragmentation is high, but has the advantage that it might > eventually still be usable if we can get blocksize > PAGE_SIZE. > > The difficulty is that when freeing dir entires you would have to be > concerned with a merging a dir_entry that is spanning the middle > of a 2^16 block.
That is easy, just don't let an entry span subblocks by not letting delete merge past the end of a subblock, just a minor tweak. New block initialization needs an outer loop on subblocks and that's it, I think.
Regards,
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