Re: [PATCH 2/2] afs: Add metadata xattrs

From: David Howells
Date: Thu Jul 06 2017 - 12:14:19 EST

Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:

> NAK. Don't overload xattrs with magic behavior just to avoid the need
> to do proper syscalls or ioctls.

How? This has to work on non-files, files you can't open and mountpoints.
You can't do an ioctl() on a file opened O_PATH:

if (unlikely(f->f_flags & O_PATH)) {
f->f_mode = FMODE_PATH;
f->f_op = &empty_fops;
return 0;

and you can't specify AT_NO_AUTOMOUNT or AT_NO_FOLLOW to openat(), so ioctl()
is of no use here.

Do you advocate introducing a pioctl() call? Linus was dead-set against that
as I recall.

I could invent a bunch of AFS-specific syscalls, but I'd rather not do that or
I suppose bring my fsinfo() patches up to scratch - but you didn't like those

Note that using xattrs for fs info is not without precedent in Linux - cifs,
for example.