Tested using md(4) memory disks to confirm multiple providers can be attached if they use the same passphrase and keyfiles, but each provider fails to attach if the passphrase / keyfile combination fails to decrypt its master key.
```
mdconfig -s 1m -u 0
mdconfig -s 1m -u 1
mdconfig -s 1m -u 2
mdconfig -s 1m -u 3
geli init md0 # set password to "test"
geli init md1 # set password to "test"
geli init md2 # set password to "test123"
geli init md3 # set password to "test"
geli attach -v md0 md1 # enter password "test"
geli status
geli detach md0 md1
geli attach -v md0 md1 md2 md3 # enter password "test"
geli status
geli detach md0 md1 md3
mdconfig -s 1m -u 4
mdconfig -s 1m -u 5
mdconfig -s 1m -u 6
dd if=/dev/random of=/tmp/test.key bs=64 count=1
echo te > /tmp/pass1.txt
echo st > /tmp/pass2.txt
geli init -s 4096 -K /tmp/test.key -J /tmp/pass1.txt -J /tmp/pass2.txt md4
geli init -s 4096 -K /tmp/test.key md5
geli init -s 4096 -K /tmp/test.key -J /tmp/pass1.txt -J /tmp/pass2.txt md6
geli attach -k /tmp/test.key -j /tmp/pass1.txt -j /tmp/pass2.txt -v md4 md5 md6
geli status
geli detach md4 md6
mdconfig -d -u 0
mdconfig -d -u 1
mdconfig -d -u 2
mdconfig -d -u 3
mdconfig -d -u 4
mdconfig -d -u 5
mdconfig -d -u 6
rm /tmp/test.key /tmp/pass1.txt /tmp/pass2.txt
```
Expected output:
```
Attached to md0.
Attached to md1.
Done.
Name Status Components
md0.eli ACTIVE md0
md1.eli ACTIVE md1
Attached to md0.
Attached to md1.
geli: Wrong key for md2.
Attached to md3.
geli: At least one provider failed to attach.
Name Status Components
md0.eli ACTIVE md0
md1.eli ACTIVE md1
md3.eli ACTIVE md3
Attached to md4.
geli: Wrong key for md5.
Attached to md6.
geli: At least one provider failed to attach.
Name Status Components
md4.eli ACTIVE md4
md6.eli ACTIVE md6
```