linux-ext4 - Re: [PATCH] e2fsck: Correct ext4 dates generated by old kernels

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Message-ID: <20151125094632.GA2632@thunk.org>
Date:	Wed, 25 Nov 2015 04:46:32 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	David Turner <novalis@...alis.org>
Cc:	Andreas Dilger <adilger@...ger.ca>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] e2fsck: Correct ext4 dates generated by old kernels

On Wed, Nov 25, 2015 at 01:01:35AM -0500, David Turner wrote:
> On Tue, 2015-11-24 at 14:34 -0700, Andreas Dilger wrote: 
> > +static int check_inode_extra_negative_epoch(__u32 xtime, __u32
> > extra) {
> > +	return (xtime & (1 << 31)) != 0 &&
> 
> On a re-read, I think the bitshift is technically undefined behavior
> because 1 is signed and 2**31 is not representable as a signed (32-bit)
> int. Changing it to 1U should fix it.

Instead of doing all of the bitshifts, I was thinking about doing
something much simpler:

	...
	if (inode->ctime_hi == 3 && fix_problem(....)
		inode->ctime_hi = 0;
	if (inode->mtime_hi == 3 && fix_problem(....)
		inode->mtime_hi = 0;

Hmm?  That should work just as well, and is easier to read and
understand what's going on, and matches with the test we are using in
the kernel.

					- Ted
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