Re: utimensat EACCES vs. EPERM in 4.8+

Hi Miklos,

On 01/17/2017 10:39 PM, Miklos Szeredi wrote:

On Tue, Jan 17, 2017 at 8:57 AM, Cyril Hrubis [off-list ref] wrote:

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Hi!

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Jan, thanks for spotting this.

Credit goes to Cyril. As for LTP-20170116 (released yesterday) we went
with current documented behavior - few failures are expected on 4.8+.

Actually credit goes to SUSE QAM that caught the change on kernel
update :-).

And while this makes for a nice discussion, it is almost completely
irrelevant in real life, since the only thing broken by this change
will be test suites (in other words immutable files are rare as hen's
teeth).

While I agree that the chances of breakage may be quite small (though
I certainly won't be so bold as to assert that only test suites
will get broken), your comment misses the important metapoint:
changes like this should not just be getting waved through the gate
without some analysis along the lines of what I did. "Consistency"
and an (incorrect) assertion that "In most cases, EPERM is returned
on immutable inode" just don't cut it, when it comes to making
changes of this sort.

If you find that this change actually breaks something other than a
test suite, then yes, please lets revert it.  

No. That is not a strategy. I already said it, but I'll say it again:
sometimes these reports only arrive many months or even years later.
And then we can end up with fiascoes such as F_SETOWN/F_SETOWN_EX.
(Essentially: F_SETOWN got subtly changed, and by the time people
realized the breakage had occurred it was *years* late. Too late to
revert... So, then we got F_SETOWN_EX to allow us what F_SETOWN
used to do. See fcntl(2).)

Otherwise there's not
much point (distros can revert it for themselves if they want be
paranoid).

Also not a strategy; distros don't want to carry such junk
patches.

All of this said, I still don't know whether reverting the patch
is warranted...

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/