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Re: [Qemu-block] [PATCH v2 2/4] tests/qemu-iotests/group: Remove some mo

From: Eric Blake
Subject: Re: [Qemu-block] [PATCH v2 2/4] tests/qemu-iotests/group: Remove some more tests from the "auto" group
Date: Tue, 16 Jul 2019 11:09:56 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0

On 7/16/19 10:58 AM, Max Reitz wrote:

>>> Ah, OK.  So, uh, we effectively can’t run any Python tests on macOS?
>> Not when our CI is set up to use super-long file names:
>> +  File
>> "/private/var/folders/sy/2x5qvs0n4lg18fry9jz4y21m0000gn/T/cirrus-ci-build/tests/qemu-iotests/../../python/qemu/machine.py",
>> line 294, in launch
> That isn’t really long.

The MacOS limit is 104 (or 103 if you insist on using the trailing NUL
yourself), compared to Linux at 108 (107).  And:

$ printf
| wc -c

shows that we are right on the verge of overflowing the space allotted,
with any socket name worth using when the socket lives inside

>> Is there any way to create our sockets somewhere under /tmp instead of
>> inside tests/qemu-iotests, so that we have a shorter filename for
>> sockets no matter how deep in the file hierarchy the tests themselves live?
>> Also, at one point, we tossed around the idea of
>> s/qemu-iotests/iotests/, to shave off 5 characters that don't really add
>> anything.
> I’d personally rather just skip the iotests if we detect such a silly
> OS, but maybe that’s just me.

It's a rather unfortunate limit, but it's not all that silly (the limit
is based on the fact that struct sockaddr has to fit inside a nice
power-of-2 structure somewhere in the kernel, and enough else is used
that you really are left with just 104/108 bytes, or even 92 bytes if
you use HP-UX 11).  POSIX does not place a minimum length on sun_path,
but I know of no system that does not allow at least 92 bytes, if you
are aiming for a portably-small name.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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