linux-kernel - Re: [PATCH] btrfs: bugfix: handle FS_IOC32_{GETFLAGS,SETFLAGS,GETVERSION} in btrfs

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Date:	Thu, 14 May 2015 16:27:54 +0000
From:	Luke Dashjr <luke@...hjr.org>
To:	dsterba@...e.cz
Cc:	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, trivial@...nel.org
Subject: Re: [PATCH] btrfs: bugfix: handle FS_IOC32_{GETFLAGS,SETFLAGS,GETVERSION} in btrfs_ioctl

On Thursday, May 14, 2015 2:06:17 PM David Sterba wrote:
> On Wed, May 13, 2015 at 05:15:26PM +0000, Luke Dashjr wrote:
> > 32-bit ioctl uses these rather than the regular FS_IOC_* versions. They
> > can be handled in btrfs using the same code. Without this, 32-bit
> > {ch,ls}attr fail.
> 
> Yes, but this has to be implemented in another way. See eg.
> https://git.kernel.org/linus/e9750824114ff

I don't see what is different with that implementation. All f2fs_compat_ioctl 
does is change cmd to the plain-IOC equivalent and call f2fs_ioctl with the 
same arg (compat_ptr merely causes a cast to void* and back, which AFAIK is a 
noop on 64-bit?). Am I missing something? I could try to just imitate it, but 
I'd rather know what is significant/going on to ensure I don't waste your time 
with code I don't even properly understand myself.

Perhaps by coincidence, the patch does at least in practice work (although at 
least `btrfs send` appears to be broken still, and I'm at a loss for how to 
approach fixing that).

Luke
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