On Thu, Jun 29, 2017 at 10:25:28AM -0700, Darrick J. Wong wrote:

Was there ever a version of NFS (or more generally callers of the
exportfs code) that couldn't deal with i_generation in the file handle,
and therefore we invented this generation hack to work around the loss
of the generation information?

There's a comment in xfs_fs_encode_fh about not supporting 64bit inodes
with subtree_check (which seems to require one ino/gen pair for the file
and a second pair for the file's parent) on NFSv2 because v2 doesn't
provide enough space for all the file handle information, but that's the
furthest I got with lazy-mining the git history. :)

There's a comment in fs/ext4/super.c:ext4_nfs_get_inode

	* Currently we don't know the generation for parent directory, so
	* a generation of 0 means "accept any"

But I don't see that used.

It was used once upon a time; I see it actually used in old 2.5 code in
nfsd_get_dentry.  Hm.

--b.