Initialize newly allocated buffer

[behlendorf]

Description

When allocating a buffer using zio_buf_alloc() or an ABD with
abd_alloc_for_io() ensure the returned memory is initialized
to zero.

How Has This Been Tested?

Manual verification and a test run of the ZTS.

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)
• 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.

[ahrens]

When allocating a buffer using zio_buf_alloc(), or an ABD with abd_alloc_for_io(), ensure the returned memory is initialized to zero.

Reading this, it sounds like you're saying that zio_buf_alloc/abd_alloc_for_io should return zeroed buffers, which could have a substantial performance impact. However, the code changes relate specifically to handling encryption, where perhaps performance isn't a concern?

I see that this is marked as "code cleanup", not "bug fix". I presume that spa_do_crypt_abd() completely fills the target abd, so the current code (without zeroing) is correct. How does zeroing these buffers make the code more clear?

[behlendorf]

I've gone ahead and moved the initialization down in to zio_crypt_init_uios_zil() so it's only applied where it's needed.