Re: Linux 2.6 nanosecond time stamp weirdness breaks GCC build

[Andi Kleen <ak@suse.de>]

On Thu, 1 Apr 2004 21:28:20 +0200 (CEST)
Ulrich Weigand <weigand@i1.informatik.uni-erlangen.de> wrote:

> However, I'd say that this should probably be fixed in the kernel,
> e.g. by not reporting high-precision time stamps in the first
> place if the file system cannot store them ...

Interesting. We discussed the case as a theoretical possibility when
the patch was merged, but it seemed to unlikely to make it worth
complicating the first version.

The solution from back then I actually liked best was to just round
up to the next second instead of rounding down when going from 1s 
resolution to ns.

-Andi

e.g. like this for ext3 (untested). Does that fix your problem?

diff -u linux-2.6.5rc3-work/fs/ext3/inode.c-o linux-2.6.5rc3-work/fs/ext3/inode.c
--- linux-2.6.5rc3-work/fs/ext3/inode.c-o	2004-04-01 22:07:43.000000000 +0200
+++ linux-2.6.5rc3-work/fs/ext3/inode.c	2004-04-01 22:08:49.000000000 +0200
@@ -2624,9 +2624,11 @@
 	}
 	raw_inode->i_links_count = cpu_to_le16(inode->i_nlink);
 	raw_inode->i_size = cpu_to_le32(ei->i_disksize);
-	raw_inode->i_atime = cpu_to_le32(inode->i_atime.tv_sec);
-	raw_inode->i_ctime = cpu_to_le32(inode->i_ctime.tv_sec);
-	raw_inode->i_mtime = cpu_to_le32(inode->i_mtime.tv_sec);
+	/* round up because we cannot store nanoseconds. This avoids
+	   the time jumping back when the inode is loaded again. */
+	raw_inode->i_atime = cpu_to_le32(inode->i_atime.tv_sec + 1);
+	raw_inode->i_ctime = cpu_to_le32(inode->i_ctime.tv_sec + 1);
+	raw_inode->i_mtime = cpu_to_le32(inode->i_mtime.tv_sec + 1);
 	raw_inode->i_blocks = cpu_to_le32(inode->i_blocks);
 	raw_inode->i_dtime = cpu_to_le32(ei->i_dtime);
 	raw_inode->i_flags = cpu_to_le32(ei->i_flags);