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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 5 Oct 2017 18:31:29 -0700
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Subject: Re: [PATCH] vfs: fix statfs64() returning impossible EOVERFLOW for
 64-bit f_files
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Sergey Klyaus <sergey.m.klyaus@gmail.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Li Wang <liwang@redhat.com>,
        Andreas Dilger <adilger@dilger.ca>,
        Andi Kleen <andi.kleen@intel.com>
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On Thu, Oct 5, 2017 at 4:06 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> Just to make sure we are on the same page: out of kstatfs fields
> we have 5 u64 ones (see above; all of them are u64 is struct statfs64
> on all architectures), an opaque 64bit f_fsid and 5 fields that
> are long: f_type (magic numbers, all 32bit), f_namelen (max filename
> length), f_frsize (0 on most of filesystems, always fits into 32 bits),
> f_flags (guaranteed to be 32bit) and f_bsize.

Please just use that FITS_IN() kind of macro regardless.

If the sizes match, the compiler will optimize the test away.

If the sizes don't match, that FITS_IN() will do the right thing.

Do *not* manually go and say "these fields are ok, because..". The
whole bug was because people were confused about the field widths.

                 Linus