zdb: fix checksum calculation for decompressed blocks

[andriytk]

Currently, when reading compressed blocks with -R and decompressing them with :d option and specifying lsize, which is normally bigger than psize for compressed blocks, the checksum is calculated on decompressed data. But it makes no sense since zfs always calculates checksum on physical, i.e. compressed data. So reading the same block produces different checksum results depending on how we read it, whether we decompress it or not, which, again, makes no sense.

For example:

$ sudo ./zdb -R mypool 0:beb7f6e7e000:1000:c | grep fletcher4
   fletcher4	cksum=00000088174743b9:00019b84088c35af:02827051a621db13:b0ca19b0de96b688
$ sudo ./zdb -R mypool 0:beb7f6e7e000:4000/1000:dc | grep fletcher4
   fletcher4	cksum=0000021a4433878e:001188edf8682c10:6280e56d3358da45:d2900132b1add9dd

Fix: use psize instead of lsize when calculating the checksum so that it is always calculated on the physical block size, no matter was it compressed or not.

Here's how the same example works with the fix:

$ sudo ./zdb -R mypool 0:beb7f6e7e000:1000:c | grep fletcher4
   fletcher4	cksum=00000088174743b9:00019b84088c35af:02827051a621db13:b0ca19b0de96b688
$ sudo ./zdb -R mypool 0:beb7f6e7e000:4000/1000:dc | grep fletcher4
   fletcher4	cksum=00000088174743b9:00019b84088c35af:02827051a621db13:b0ca19b0de96b688

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[behlendorf]

Yes, we should definitely be using the psize here. Thanks for noticing and opening up a fix.