FUSE extended attribute patches available

[Julian Elischer]

On 5/03/2016 7:06 PM, Rick Macklem wrote:
> Ken Merry wrote:
>> I have patches for FreeBSD’s FUSE filesystem kernel module to support
>> extended attributes:
oh showing off your masochistic side eh?

>> https://people.freebsd.org/~ken/fuse_extattr.20160229.1.txt
>>
I spent an hour beating my head against fuse yesterday.
then realised that it's an old version on our product. We really have 
to get off 8.0
(hopefully a matter of weeks now to a 10.x switch)
Now all I need is to find  a FreeBSD filesystem expert 
(ZFS/NFS/CIFS/GFS) to hire.


> The only bit of code I have that might be useful for this patch is:
>    	case FUSE_GETXATTR:
>    	case FUSE_LISTXATTR:
> ! 		/*
> ! 		 * These can have varying response lengths, and 0 length
> ! 		 * isn't necessarily invalid.
> ! 		 */
> ! 		err = 0;
> *** I came up with this:
> 		fgin = (struct fuse_getxattr_in *)
> 		    ((char *)ftick->tk_ms_fiov.base +
> 		     sizeof(struct fuse_in_header));
> 		if (fgin->size == 0)
> 			err = (blen == sizeof(struct fuse_getxattr_out)) ? 0 :
> 			    EINVAL;
> 		else
> 			err = (blen <= fgin->size) ? 0 : EINVAL;
>    		break;
> I think I got the size check right?
>
> The big question is...
> What to do with the NAMESPACE?
> - My code fails for SYSTEM and does USER without prepending "user.".
>    (That seemed to be what rwatson@ felt was reasonable. I thought our
>     discussion was on a mailing list, but I can't find it.)
>    I've cc'd him. Maybe he can comment again.
Is there  a standard for extended attributes I should knwo about?
  It seems to me that it's a bit like the wild west.
Extended attributes seem to be "every OS for himself".

>
> - If you stick with prepending "user." or "system." there needs to be
>    some way to bypass this so that attributes that don't start in "user."
>    or "system." can be accessed. I've seen "trusted." and "glusterfs."
>    on GlusterFS.
>    --> Maybe a new namespace called something like "nil" that just bypasses
>        any USER or SYSTEM checks?
>
> rick
>
>> The patch implements the get/set/delete/list extended attribute methods.  The
>> listing code also converts extended attribute lists from the Linux/FUSE
>> format to the FreeBSD format.  For example:
>>
>> # touch foo
>> # ls -la foo
>> -rwxrwxrwx  1 root  wheel  0 Feb 29 21:40 foo
>> # lsextattr user foo
>> foo
>> # setextattr user testattr1 "12345678" foo
>> # lsextattr user foo
>> foo     testattr1
>> # getextattr user testattr1 foo
>> foo     12345678
>> # setextattr user testattr2 "87654321" foo
>> # lsextattr user foo
>> foo     testattr2       testattr1
>> # rmextattr user testattr1 foo
>> # lsextattr user foo
>> foo     testattr2
>> # getextattr user testattr1 foo
>> getextattr: foo: failed: Attribute not found
>> # getextattr user testattr2 foo
>> foo     87654321
>>
>>
>> Just to be clear on what this does, it only provides extended attribute
>> support to FreeBSD applications if the underlying FUSE filesystem implements
>> FUSE extended attribute support.  Many FUSE filesystems don’t support the
>> extended attribute VFS operations.
>>
>> I have tested this out on IBM’s LTFS implementation, but I have not yet found
>> another FUSE filesystem that supports extended attributes.  If anyone knows
>> of one, please let me know so I can try it out.  (I looked through a number
>> of the filesystems in sysutils/fusefs* in the ports tree.)
>>
>> Any feedback is welcome.  I’m planning to check this into FreeBSD/head in the
>> next week or so.
>>
>> Obviously, I’ve also ported IBM’s LTFS implementation to FreeBSD.  It works
>> in the standard FUSE mode, and you can also link it into an application as a
>> library if you don’t want to incur the overhead of running through FUSE.  I
>> haven’t gotten around to packaging it up to go out for testing / review.
>>
>> If anyone has IBM LTO-5 or newer tape drives, or IBM TS1140 or newer tape
>> drives, and wants to try it out, let me know.  I’ll send you the code when
>> I’ve got it at least somewhat ready.  This is IBM-specific, and won’t work
>> on HP tape drives.
>>
>> Ken
>> —
>> Ken Merry
>> ken at FreeBSD.ORG
>>
>>
>>
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