(added linux-nfs@xxxxxxxxxxxxxxx) On Tue, Apr 05 2016, Richard Weinberger wrote: > Hi! > > Currently UBIFS is not exportable. > I'm not sure whether it is completely impossible or if I just miss a detail. > So I've some questions. > > Documentation/filesystems/nfs/Exporting states that the only required function > is fh_to_dentry(). > This function should on UBIFS be implementable using generic_fh_to_dentry(). > While UBIFS reuses in theory inode numbers we can ignore i_generation as > the flash chip is long dead before we start reusing inodes. Same as for JFFS2. > But the same document states also that fh_to_parent() and get_parent() are optional > but strongly recommended. > What does this mean? Will NFS work but puppies die and turn into > zombies? Not puppies, just kittens. If you don't provide these functions, then exporting with "subtree_check" won't work. That is no great loss except that people might find the failure confusing. > > Implementing get_parent() is a little unpleasant. > UBIFS's on-flash layout does not support querying the parent. > We could change UBIFS's struct ubifs_ino_node, but I'd change the > on-flash layout only as last resort. > > The biggest problem I see is that UBIFS does not really support telldir() > and seekdir(). > Directory offsets in UBIFS are plain hash values, so telldir()/seekdir() won't > correctly work if UBIFS faces hash collisions. > Currently UBIFS implements a hack which stores the UBIFS dent object into > file->private_data such that consecutive readdir()s are guaranteed to work. > A comment on UBIFS's readdir states: > * This means that UBIFS cannot support NFS which requires full > * 'seekdir()'/'telldir()' support. > > Is this still true? Maybe we can have NFS even if it is not perfect in > terms of performance. How big are your hashes? ext3 messed up their readdir/telldir design too so they don't have guaranteed unique keys. When using 32bit hashes you can definitely get problems with collisions. I have not heard of problems with 64bit hashes. I may have the details slightly wrong, but as I recall non-uniqueness of cookies only causes a problem when the last cookie returned in a READDIR reply matches the first cookie returned in reply to the next readdir. So non-uniqueness is only a problem when it aligns badly. NeilBrown > > Artem, did I miss another show stopper? :-) > > Thanks, > //richard > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html
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