fs-verity: support reading signature with ioctl

Add support for FS_VERITY_METADATA_TYPE_SIGNATURE to
FS_IOC_READ_VERITY_METADATA.  This allows a userspace server program to
retrieve the built-in signature (if present) of a verity file for
serving to a client which implements fs-verity compatible verification.
See the patch which introduced FS_IOC_READ_VERITY_METADATA for more
details.

The ability for userspace to read the built-in signatures is also useful
because it allows a system that is using the in-kernel signature
verification to migrate to userspace signature verification.

This has been tested using a new xfstest which calls this ioctl via a
new subcommand for the 'fsverity' program from fsverity-utils.

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Victor Hsieh <[email protected]>
Reviewed-by: Jaegeuk Kim <[email protected]>
Reviewed-by: Chao Yu <[email protected]>
Signed-off-by: Eric Biggers <[email protected]>

0 files changed, 0 insertions, 0 deletions