I am trying to build the `docker' package on a foreign distro.
Specifically, Debian sid. This results in the following test failures:

--------------------------------------
=== Failed
=== FAIL: daemon/graphdriver/quota TestBlockDev/testBlockDevQuotaDisabled (0.03s)
    --- FAIL: TestBlockDev/testBlockDevQuotaDisabled (0.03s)
        projectquota_test.go:83: assertion failed: error is not nil: exit status 1: mount failed: mount: /tmp/guix-build-docker-19.03.7.drv-0/xfs-mountPoint-325789281: mount failed: Operation not permitted.
            

=== FAIL: daemon/graphdriver/quota TestBlockDev/testBlockDevQuotaEnabled (0.02s)
    --- FAIL: TestBlockDev/testBlockDevQuotaEnabled (0.02s)
        projectquota_test.go:83: assertion failed: error is not nil: exit status 1: mount failed: mount: /tmp/guix-build-docker-19.03.7.drv-0/xfs-mountPoint-054602316: mount failed: Operation not permitted.
            

=== FAIL: daemon/graphdriver/quota TestBlockDev/testSmallerThanQuota (0.01s)
    --- FAIL: TestBlockDev/testSmallerThanQuota (0.01s)
        projectquota_test.go:83: assertion failed: error is not nil: exit status 1: mount failed: mount: /tmp/guix-build-docker-19.03.7.drv-0/xfs-mountPoint-879061307: mount failed: Operation not permitted.
            

=== FAIL: daemon/graphdriver/quota TestBlockDev/testBiggerThanQuota (0.01s)
    --- FAIL: TestBlockDev/testBiggerThanQuota (0.01s)
        projectquota_test.go:83: assertion failed: error is not nil: exit status 1: mount failed: mount: /tmp/guix-build-docker-19.03.7.drv-0/xfs-mountPoint-487602526: mount failed: Operation not permitted.
            

=== FAIL: daemon/graphdriver/quota TestBlockDev/testRetrieveQuota (0.01s)
    --- FAIL: TestBlockDev/testRetrieveQuota (0.01s)
        projectquota_test.go:83: assertion failed: error is not nil: exit status 1: mount failed: mount: /tmp/guix-build-docker-19.03.7.drv-0/xfs-mountPoint-717635877: mount failed: Operation not permitted.
            

=== FAIL: daemon/graphdriver/quota TestBlockDev (0.38s)
    projectquota_test.go:50: meta-data=/tmp/guix-build-docker-19.03.7.drv-0/xfs-image973358730 isize=256    agcount=4, agsize=4096 blks
                 =                       sectsz=512   attr=2, projid32bit=1
                 =                       crc=0        finobt=0, sparse=0, rmapbt=0
                 =                       reflink=0
        data     =                       bsize=4096   blocks=16384, imaxpct=25
                 =                       sunit=0      swidth=0 blks
        naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
        log      =internal log           bsize=4096   blocks=853, version=2
                 =                       sectsz=512   sunit=0 blks, lazy-count=1
        realtime =none                   extsz=4096   blocks=0, rtextents=0
--------------------------------------

This suggests that there's an issue with permissions. I recalled that
Debian ships a custom kernel patch that disables unprivileged
namespaces by default. However, after setting

    kernel.unprivileged_userns_clone = 1

the problem persisted.

I am attaching the full build log.