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Date:   Tue, 25 Jan 2022 22:13:58 +0000
From:   Eric Biggers <ebiggers@kernel.org>
To:     Harry Austen <harryausten@hotmail.co.uk>
Cc:     linux-f2fs-devel@lists.sourceforge.net, jaegeuk@kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix fileattr_set unsupported attribute
 handling
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On Tue, Jan 25, 2022 at 10:01:49PM +0000, Harry Austen wrote:
> On Monday, 24 January 2022 19:25:44 GMT Eric Biggers wrote:
> > On Sat, Jan 22, 2022 at 12:59:03PM +0000, Harry Austen wrote:
> > > FS_IOC_SETFLAGS ioctl should return EOPNOTSUPP if the file attribute
> > > (e.g. FS_NOCOW_FL) is not supported, rather than silently ignoring it
> > > and returning success.
> > > 
> > > Fixes: 9b1bb01c8ae7 (f2fs: convert to fileattr)
> > > Signed-off-by: Harry Austen <harryausten@hotmail.co.uk>
> > > ---
> > > 
> > >  fs/f2fs/file.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > > index 92ec2699bc85..061bf35c2582 100644
> > > --- a/fs/f2fs/file.c
> > > +++ b/fs/f2fs/file.c
> > > @@ -3085,9 +3085,8 @@ int f2fs_fileattr_set(struct user_namespace
> > > *mnt_userns,> 
> > >  		return -EIO;
> > >  	
> > >  	if (!f2fs_is_checkpoint_ready(F2FS_I_SB(inode)))
> > >  	
> > >  		return -ENOSPC;
> > > 
> > > -	if (fsflags & ~F2FS_GETTABLE_FS_FL)
> > > +	if (fsflags & ~F2FS_SETTABLE_FS_FL)
> > > 
> > >  		return -EOPNOTSUPP;
> > > 
> > > -	fsflags &= F2FS_SETTABLE_FS_FL;
> > > 
> > >  	if (!fa->flags_valid)
> > >  	
> > >  		mask &= FS_COMMON_FL;
> > 
> > This is intentional, and matches what ext4 does; see the comment in the ext4
> > implementation of this:
> > 
> >         /*
> >          * chattr(1) grabs flags via GETFLAGS, modifies the result and
> >          * passes that to SETFLAGS. So we cannot easily make SETFLAGS
> >          * more restrictive than just silently masking off visible but
> >          * not settable flags as we always did.
> >          */
> 
> Ah, my apologies. I thought it looked a little too obvious. Clearly I
> should have looked at the ext4 code. Please disregard this patch.
> 
> Is there anything else that could be done to improve unsettable
> attribute handling? For example, is there a reason FS_NOCOW_FL is
> gettable but not settable? Could it be added to the settable list?

A lot of flags are gettable by FS_IOC_GETFLAGS but not settable by
FS_IOC_SETFLAGS, typically because they can only be set through a dedicated
interface.  For example, the encrypt flag can only be set using
FS_IOC_SET_ENCRYPTION_POLICY, or via inheritance.

> > 
> > Also, even if this patch was correct, the Fixes tag is wrong.
> 
> Having looked at this a bit more, I assume you are saying this due to
> the missing double quotes around the commit summary? (just so I know for
> next time as this is my first attempt at sending a kernel patch)
> 

There's that, but more importantly the commit you listed is wrong.  The relevant
code was added by an earlier commit, and that commit just moved it.

- Eric