When the kernel supports the new fscrypt key management ioctls, use them
instead of add_key() and keyctl_unlink().
This will be needed in order to support v2 encryption policies, since v2
encryption policies only support the new ioctls.
The new ioctls have other advantages too. For example,
FS_IOC_REMOVE_ENCRYPTION_KEY automatically evicts exactly the necessary
kernel objects, so the drop_caches sysctl is no longer needed. This
makes evicting keys faster and more reliable.
FS_IOC_REMOVE_ENCRYPTION_KEY also detects if any files are still open
and therefore couldn't be "locked", whereas this went undetected before.
Therefore, to start out this patch adds support for using the new ioctls
for v1 encryption policies, i.e. on existing devices.
(Originally based on a patch by Satya Tangirala <satyat@google.com>)
Bug: 140500828
Test: tested that a device using v1 policies continues to work, both
with and without an updated kernel. See
If64028d8580584b2c33c614cabd5d6b93657f608 for more details.
Also checked via the log that the filesystem-level keyring is in
fact used when supported.
Change-Id: I296ef78138578a3fd773797ac0cd46af1296b959
