Re: [PATCH v2] btrfs-progs: build system: Fix the test for EXT4_EPOCH_MASK

[David Sterba <dsterba@suse.cz>]

On Sun, Mar 14, 2021 at 07:49:13PM +0100, Pierre Labastie wrote:
> After sending the first version of the patch, I realized that it
> was flawed, because of some formatting by the MUA. It took me
> some time to set up an MTA so that git send-email works. Now the
> patch should apply cleanly. Please remove the present paragraph by using
> git am -c. Apologies for the inconvenience(s).
> -- >8 --
> Commit b3df561fbf has introduced the ability to convert extended
> inode time precision on ext4, but this breaks builds on older distros,
> where ext4 does not have the nsec time precision.
> 
> Commit c615287cc tried to fix that by testing the availability of
> the EXT4_EPOCH_MASK macro, but the test is not complete.
> 
> This patch aims at fixing the macro test, and changes the
> name of the associated HAVE_ macro, since the logic is reverted.
> 
> This fixes #353 when ext4 has nsec time precision. Note that
> the test fails when ext4 does not have the nsec time precision.
> Maybe the test shouldn't be run in that case?

Good point. What's the way to find that out? We can create a sample
ext4 filesystem and do a runtime check or parse it out of debugfs dump
looking for the features. I think it's the 'extra_isize', that's what
manual page ext4 says and that the patch adding 64bit timestamp support
checks when reading the extended timestamps.