extended attributes

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

Hello

As far as I understand, here is the status of extended attributes on 
NetBSD:

- available on NetBSD-current on UFS1 filesystems. One has to build 
a kernel with options UFS_EXTATTR and UFS_EXTATTR_AUTOSTART, and any
attribute you want to use needs a backend. extattrctl initattr and
extattrctl enable are used to create the backends.

- available on netbsd-5 with the same limitation as NetBSD-current,
plus pullup 1624 that needs to be applied otherwise it is unusable.

- not available on any NetBSD version with UFS2 filesystems.

In a nutshell, the only way to go on NetBSD is UFS1 and you need to create
attribute backends. I would like to make this more usable by removing the
backend creation requirement. It seems that we could add a create flag to
src/sys/ufs/ufs/ufs_extattr.c:ufs_extattr_find_attr() so that 
ufs_extattr_set() coould have the opportunity to request attribute
storage creation. 

Such a behavior could be triggered by a new kernel option such
as UFS_EXTATTR_AUTOCREATE. It could hold the default size for autocreated
attributes. (e.g.: options UFS_EXTATTR_AUTOCREATE=1024 to get 1024 bytes
long attributes). 

Opinions?

-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost