Bug#854400: systemd: FTBFS if /tmp is an overlayfs

[James Cowgill]

Source: systemd
Version: 232-15
Severity: important

Hi,

While testing #852811 I discovered that systemd does not build within an
overlayfs schroot (which all my mips chroots are setup as). Specifically
the "test-copy" test fails with:

> FAIL: test-copy
> ===============
> 
> test_copy_file
> test_copy_file_fd
> test_copy_tree
> Assertion 'access(f, F_OK) == 0' failed at ../src/test/test-copy.c:136, function test_copy_tree(). Aborting.
> FAIL test-copy (exit status: 134)

The assertion is caused by a file not being copied by copy_tree and that
is in turn caused by this line:
https://sources.debian.net/src/systemd/232-15/src/basic/copy.c/#L342

The above line does not copy files if the device of the file is not the
same as the device of the parent directory, however on an overlayfs
filesystem this is condition is always true for non-directories.

From https://www.kernel.org/doc/Documentation/filesystems/overlayfs.txt:
> This approach is 'hybrid' because the objects that appear in the
> filesystem do not all appear to belong to that filesystem.  In many
> cases an object accessed in the union will be indistinguishable
> from accessing the corresponding object from the original filesystem.
> This is most obvious from the 'st_dev' field returned by stat(2).
> 
> While directories will report an st_dev from the overlay-filesystem,
> all non-directory objects will report an st_dev from the lower or
> upper filesystem that is providing the object.  Similarly st_ino will
> only be unique when combined with st_dev, and both of these can change
> over the lifetime of a non-directory object.  Many applications and
> tools ignore these values and will not be affected.

Note that this behavior is different from say 'cp -Rx'. cp only checks
the value of st_dev if the file is a directory. This allows it to work
correctly with overlayfs.
http://sources.debian.net/src/coreutils/8.26-2/src/copy.c/?hl=2547#L2547

Thanks,
James

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