Extended attributes limit in Linux

[Sun_Blood]

On Sun, Feb 2, 2014 at 10:37 PM, Dave Chinner <david at fromorbit.com> wrote:

> On Fri, Jan 31, 2014 at 04:54:52PM +0800, Jeff Liu wrote:
> > Hello,
> >
> > On 01/31 2014 15:40 PM, Sun_Blood wrote:
> > > Hello,
> > >
> > > If I understands it correctly XFS don't have a limit to the size of
> > > extended attributes(EA) but Linux impose a limit at 64k.
> > > What I am trying to do is build a backup server that our Apple
> computers
> > > will use together with rsync to backup files to. The problem I face is
> > > that Apple HFS+ don't have a limit to EA so it has files with more then
> > > 64k of EA in it.
> > >
> > > The Linux Kernel has a limit imposed to it in include/linux/limits.h
> > >
> > >     #defineXATTR_SIZE_MAX 65536   /* size of an extended attribute
> value
> > >     (64k) */
> > >
> > >     #defineXATTR_LIST_MAX 65536   /* size of extended attribute
> namelist
> > >     (64k) */
> > >
> >
> > Yes, 64k is the VFS limit per EA value size.
>
> XFS has a limit of 64k as well. I suspect that we could handle
> larger EAs without too much problem as we already have the concept
> of a "remote EA" that is allocated outside of the attribute btree
> (but still inside the attribute address space). The problem with
> them is that they are written synchronously, and so large attributes
> written this way are slow operations.
>
> Still, until the VFS limit is lifted and we do a bunch more work to
> avoid XATTR_SIZE_MAX allocations everywhere there's no point looking
> at raising the XFS limit....
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david at fromorbit.com
>

Ok. Just for fun how could we proceed to get the VFS limit lifted? Or any
other way to handle this problem?
It would be nice to be able to say that XFS is the only file system
available fully compatible with OS X HFS+ =)

/Martin
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