calcsize locks /dev/null? Why?

Hi,

we run into trouble with the amanda-client on a host running dockerd.
Dockerd has a shared lock on /dev/null. (Do not ask why.)

The calcsize program of the amanda-client suite tries to get an
exclusive lock on its FD 1 (which is opened to /dev/null).

Because of dockerd holding the shared lock already, the estimater gets
stuck.

See client-src/calsize.c ~ line 360 (Amanda 3.3.9)

What's the purpose of this lock? Just for serializing the estimater
runs? If so, we should not make us dependend on some other software by
conflicting with their locks.

    Best regards from Dresden/Germany
    Viele Grüße aus Dresden
    Heiko Schlittermann
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