rsync -u --inplace --partial -a can't resume transfer

A reproducible test:

~$ cd /tmp/
/tmp$ mkdir a b
/tmp$ cd a
/tmp/a$ head -c 100000 /dev/urandom > test
/tmp/a$ ls -l test
-rw-r--r-- 1 nahuel nahuel 100000 Jan 27 18:27 test
/tmp/a$ cd ../b
/tmp/b$ timeout 3 rsync -u --inplace --partial --bwlimit=2k --progress -va ../a/test .
sending incremental file list
test
         32,768 32% 0.00kB/s 0:00:00
rsync error: received SIGINT, SIGTERM, or SIGHUP (code 20) at rsync.c(632) [sender=3.1.1]
rsync error: received SIGINT, SIGTERM, or SIGHUP (code 20) at io.c(504) [generator=3.1.1]
/tmp/b$ ls -l test
-rw------- 1 nahuel nahuel 0 Jan 27 18:28 test
/tmp/b$ timeout 3 rsync -u --inplace --partial --bwlimit=2k --progress -va ../a/test .
sending incremental file list

sent 59 bytes received 12 bytes 142.00 bytes/sec
total size is 100,000 speedup is 1,408.45
/tmp/b$ ls -l test
-rw------- 1 nahuel nahuel 0 Jan 27 18:28 test
nahuel@serge:/tmp/b$

rsync version: rsync version 3.1.1 protocol version 31
ubuntu version: 3.1.1-3ubuntu1

Researching more, I see POSIX has NO way to disable mtime updating while calling write()'s, so there is no way to atomically leave a partial file with an mtime=0 mark while using --inplace.

"rsync --update --partial" (no --inplace) can do it because it transfers first to a temporal file, then updates his mtime (to 0 if unsuccessful, or to the original file mtime if transfer completed), and then rename()'s the file.

So now I think this can't be solved, but a warning should be placed in the rsync manpage about this "-u --partial" unexpected behavior. Take this as a documentation bug.

Hello Nahuel,

According to your reasoning I assume the "root" issue should still affect the versions of rsync shipped with the newer Ubuntu releases.

I agree it would be nice for the behavior you describe to be documented, but I don't think it's worth patching the Ubuntu package for it. I recognize we have a papercut here, but I don't think the fix for it belongs to Ubuntu; it should instead be driven (and thus also validated) upstream. For this reason I'm marking this bug as a Won't Fix. Should you disagree with my assessment please comment back and set the bug status back to New, we'll look at it again. Thanks!

Hello Paride, 4 years have passed from my initial report, I forgot completely about this bug :)

Fine, I will post this issue to upstream.

Reported to upstream at: https://github.com/WayneD/rsync/issues/236

Thanks Nahuel! We're doing some retriage and cleanup of old bugs, and I stumbled on this one :-)

I linked your upstream bug report to this bug, Launchpad will keep its status in sync. You may have noticed that I didn't set the status of this bug to Wontfix but to Opinion ("Doesn't fit with the project, but can be discussed"), I think it fits better.