linux-kernel - Re: [PATCH] tmpfs: Don't use 64-bit inodes by defulat with 32-bit ino

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Date:   Fri, 5 Feb 2021 15:32:38 -0600
From:   Seth Forshee <seth.forshee@...onical.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Hugh Dickins <hughd@...gle.com>, Chris Down <chris@...isdown.name>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tmpfs: Don't use 64-bit inodes by defulat with 32-bit
 ino_t

On Fri, Feb 05, 2021 at 01:23:13PM -0800, Andrew Morton wrote:
> On Fri, 5 Feb 2021 14:55:43 -0600 Seth Forshee <seth.forshee@...onical.com> wrote:
> 
> > On Fri, Feb 05, 2021 at 12:41:57PM -0800, Andrew Morton wrote:
> > > On Fri,  5 Feb 2021 14:21:59 -0600 Seth Forshee <seth.forshee@...onical.com> wrote:
> > > 
> > > > Currently there seems to be an assumption in tmpfs that 64-bit
> > > > architectures also have a 64-bit ino_t. This is not true; s390 at
> > > > least has a 32-bit ino_t. With CONFIG_TMPFS_INODE64=y tmpfs
> > > > mounts will get 64-bit inode numbers and display "inode64" in the
> > > > mount options, but passing the "inode64" mount option will fail.
> > > > This leads to the following behavior:
> > > > 
> > > >  # mkdir mnt
> > > >  # mount -t tmpfs nodev mnt
> > > >  # mount -o remount,rw mnt
> > > >  mount: /home/ubuntu/mnt: mount point not mounted or bad option.
> > > > 
> > > > As mount sees "inode64" in the mount options and thus passes it
> > > > in the options for the remount.
> > > > 
> > > > Ideally CONFIG_TMPFS_INODE64 would depend on sizeof(ino_t) < 8,
> > > > but I don't think it's possible to test for this (potentially
> > > > CONFIG_ARCH_HAS_64BIT_INO_T or similar could be added, but I'm
> > > > not sure whether or not that is wanted). So fix this by simply
> > > > refusing to honor the CONFIG_TMPFS_INODE64 setting when
> > > > sizeof(ino_t) < 8.
> > > 
> > > How about changing s390 Kconfig so that CONFIG_TMPFS_INODE64 is not enabled?
> > 
> > I did do that for our config. I see the s390 defconfig has it enabled,
> > so I will send a patch for that too. But the fact that it can be
> > configured that way and that the code behaves badly still seems
> > problematic.
> 
> I meant
> 
> --- a/fs/Kconfig~a
> +++ a/fs/Kconfig
> @@ -203,7 +203,7 @@ config TMPFS_XATTR
>  
>  config TMPFS_INODE64
>  	bool "Use 64-bit ino_t by default in tmpfs"
> -	depends on TMPFS && 64BIT
> +	depends on TMPFS && 64BIT && !S390
>  	default n
>  	help
>  	  tmpfs has historically used only inode numbers as wide as an unsigned
> _

Ah. s390 does appear to be the only architecture that doesn't use
unsigned long for ino_t, so that seems good to me. I can send a patch if
you want, but seems like you've already got one ...

Seth