[Bug 13317] rsync returns success when target filesystem is full

[Dan Stromberg]

On Mon, Mar 5, 2018 at 3:09 PM, just subscribed for rsync-qa from
bugzilla via rsync <rsync at lists.samba.org> wrote:
> https://bugzilla.samba.org/show_bug.cgi?id=13317
>
> --- Comment #6 from Rui DeSousa <rui.desousa at icloud.com> ---
> (In reply to Rui DeSousa from comment #5)
>
> It looks like no error is returned and result is a sparse file. I think a
> sync() would be required otherwise the file is truncated on close to meet the
> quota.

IINM, to create a sparse file, you have to seek past the concrete part
of a file (if any), and write something.

I'm not sure that a sync would change whether you've gone over your
quota.  At least, if I were designing a quota system, I'd make it
depend on what you've written to the buffer cache and disk, not disk
alone.

Here's an example of creating a sparse file:
$ /usr/local/pypy3-5.10.0/bin/pypy3
below cmd output started 2018 Mon Mar 05 04:01:55 PM PST
Python 3.5.3 (09f9160b643e, Dec 22 2017, 10:10:27)
[PyPy 5.10.0 with GCC 6.2.0 20160901] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>> file_ = open('/tmp/sparse-file', 'wb')
>>>> file_.seek(1024*1024*8)
8388608
>>>> file_.write(b'a')
1
>>>> file_.close()
>>>>
above cmd output done    2018 Mon Mar 05 04:02:14 PM PST
dstromberg at zareason2:~ x86_64-unknown-linux-gnu 4805

$ ls -l /tmp/sparse-file
below cmd output started 2018 Mon Mar 05 04:02:18 PM PST
-rw-rw-r-- 1 dstromberg dstromberg 8388609 Mar  5 16:02 /tmp/sparse-file
above cmd output done    2018 Mon Mar 05 04:02:18 PM PST
dstromberg at zareason2:~ x86_64-unknown-linux-gnu 4805

$ du -sh /tmp/sparse-file
below cmd output started 2018 Mon Mar 05 04:02:22 PM PST
4.0K    /tmp/sparse-file