Re: ZFS rename with associated snapshot present: odd error message

On 2021-May-5, at 05:28, Mark Millard <marklmi at yahoo.com> wrote:

> On 2021-May-5, at 02:47, Andriy Gapon <avg at FreeBSD.org> wrote:
> 
>> On 05/05/2021 01:59, Mark Millard via freebsd-current wrote:
>>> I had a:
>>> # zfs list -tall
>>> NAME                                       USED  AVAIL     REFER  MOUNTPOINT
>>> . . .
>>> zroot/DESTDIRs/13_0R-CA72-instwrld-norm              1.44G   117G       96K  /usr/obj/DESTDIRs/13_0R-CA72-instwrld-norm
>>> zroot/DESTDIRs/13_0R-CA72-instwrld-norm_at_dirty-style  1.44G      -     1.44G  -. . .
>>> . . .
>>> (copied/pasted from somewhat earlier) and then attempted:
>>> # zfs rename zroot/DESTDIRs/13_0R-CA72-instwrld-norm zroot/DESTDIRs/13_0R-CA72-instwrld-alt-0
>>> cannot open 'zroot/DESTDIRs/13_0R-CA72-instwrld-norm_at_dirty-style': snapshot delimiter '_at_' is not expected here
>>> Despite the "cannot open" message, the result looks like:
>>> # zfs list -tall
>>> NAME                                                       USED  AVAIL     REFER  MOUNTPOINT
>>> . . .
>>> zroot/DESTDIRs/13_0R-CA72-instwrld-alt-0                  1.44G   114G       96K  /usr/obj/DESTDIRs/13_0R-CA72-instwrld-alt-0
>>> zroot/DESTDIRs/13_0R-CA72-instwrld-alt-0_at_dirty-style      1.44G      -     1.44G  -
>>> . . .
>>> Still, it leaves me wondering if everything is okay
>>> given that internal attempt to use the old name with
>>> _at_dirty-style when it was apparently no longer
>>> available under that naming.
>>> For reference:
>>> # uname -apKU
>>> FreeBSD CA72_4c8G_ZFS 13.0-RELEASE FreeBSD 13.0-RELEASE #0 releng/13.0-n244733-ea31abc261ff-dirty: Thu Apr 29 21:53:20 PDT 2021     root_at_CA72_4c8G_ZFS:/usr/obj/BUILDs/13_0R-CA72-nodbg-clang/usr/13_0R-src/arm64.aarch64/sys/GENERIC-NODBG-CA72  arm64 aarch64 1300139 1300139
>> 
>> Cannot reproduce here (but with much simpler names and on stable/13):
>> zfs create testz/test
>> zfs snapshot testz/test_at_snap1
>> zfs rename testz/test testz/test2
>> 
>> All worked.
>> 
> 
> I've noticed that sometimes in my explorations it has been
> silent instead of complaining. I've no clue at this point
> what prior activity (or lack of activity) makes the
> difference for if a message will be generated vs. not.

One difference in context is that your above sort of sequence
generates the after-snapshot context (using some things I have
around now):

zroot/DESTDIRs/13_0R-CA53-poud                     1.45G   127G     1.45G  /usr/obj/DESTDIRs/13_0R-CA53-poud
zroot/DESTDIRs/13_0R-CA53-poud_at_test                   0B      -     1.45G  -

where my example had something more like (hand edited
the above just for illustration):

zroot/DESTDIRs/13_0R-CA53-poud                     1.45G   125G       96K  /usr/obj/DESTDIRs/13_0R-CA53-poud
zroot/DESTDIRs/13_0R-CA53-poud_at_test                1.45G      -     1.45G  -

before the rename. In other words, I'd updated the
original (almost?) completely after the snapshot
(as a side effect of my overall activity). It was
only later that I tried the rename to track a new
purpose/context that I was going to switch to.

I'm not claiming that such is sufficient to
(always? ever?) reproduce the message. I'm
just pointing out that I'd had some significant
activity on the writable file system before the
rename.

Some of my activity has been more like your test
and I'd not seen the problems from such. But it
is not a very good comparison/contrast context
so I'd not infer much. I still can not at-will
set up a context to produce the messages.



===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)