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

[samba-bugs at samba.org]

https://bugzilla.samba.org/show_bug.cgi?id=13317

--- Comment #3 from Dave Gordon <dg32768 at zoho.eu> ---
(In reply to Rui DeSousa from comment #2)

Here's a snippet from Oracle's ZFS help ...
https://docs.oracle.com/cd/E19253-01/819-5461/gitfx/index.html

"Enforcement of user and group quotas might be delayed by several seconds. This
delay means that users might exceed their quota before the system notices that
they are over quota and refuses additional writes with the EDQUOT error
message."

So, rsync(1) might
(a) successfully write a bunch of data that falls just short of the quota,
(b) "successfully" (i.e. with no reported error) write some more that takes it
over quota
(c) close the file (ignoring any result)
(d) rename the file -- which may or may not work.

ZFS probably notices the quota problem somewhere between (b) and (c), drops the
excess data, and returns EDQUOT to the close(2) call.

The success of the rename depends only on whether there is sufficient free
space at that instant; any previous failure in writing the file won't affect
the rename directly. Rename may not always need any extra space anyway.

BTW: apropos your comment about "cat" in thread
https://www.postgresql.org/message-id/E6AB850C-D05E-405B-8D4E-DE18E128F402%40icloud.com
it's not the cat that makes this reliable, it's the ssh! :)

HTH,
.Dave.

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