duperemove is stuck on NoCOW files #375
Description
The reproducer against v0.15.1:
$ dd if=/dev/urandom bs=8M count=1 > a
$ touch b
$ chattr +C b
$ cat a >> b
$ lsattr a b
---------------------- a
---------------C------ b
$ ./duperemove -d -q --batchsize=0 --dedupe-options=partial,same a b
Simple read and compare of file data found 1 instances of files that might benefit from deduplication.
<hung up>
Looking at a bit more detail duperemove seems to retry on a EINVAL error when dedupe fails:
$ strace -f -y ./duperemove -d -q --batchsize=0 --dedupe-options=partial,same a b
...
[pid 3731088] ioctl(3</mnt/archive/big/git/duperemove/a>, BTRFS_IOC_FILE_EXTENT_SAME or FIDEDUPERANGE, {src_offset=0, src_length=8388608, dest_count=1, info=[{dest_fd=4</mnt/archive/big/git/duperemove/b>, dest_offset=0}]} => {info=[{bytes_deduped=0, status=-22}]}) = 0
...