cp: Adjust the sparse file tests.

[des]

Summary

• The sparsity check was ineffective: it compared the apparent size in bytes to the actual size in blocks.
• Some of the seq commands were missing an argument.
• Based on empirical evidence, 1 MB holes are not necessarily large enough to be preserved by the underlying filesystem. Increase the hole size to 16 MB.

MFC after: 1 week
Sponsored by: Klara, Inc.

[cracauer]

LGTM

[markj]

bin/cp/tests/cp_test.sh

204

Hmm, I think this is a bit too simplistic. On ZFS I see:

markj@nuc> jot 4096 1 1 > 1
markj@nuc> du -h 1
512B    1
markj@nuc> du -hA 1
8.0K    1
markj@nuc> dd if=/dev/random of=2 bs=4K count=1
1+0 records in
1+0 records out
4096 bytes transferred in 0.000220 secs (18653284 bytes/sec)
markj@nuc> du -h 2
4.5K    2
markj@nuc> du -hA 2
4.0K    2

Neither of these files is sparse obviously, and it looks like ZFS is reporting the size of the dnode as well as a compressed size.

I can't think of a way to check for holes from the shell.

[des]

bin/cp/tests/cp_test.sh

204

That's a good point. I suppose I could write a hole detection tool in C. It's still better than the previous version (which would report every file as sparse).

[des]

Use a custom tool to detect sparseness.