block/crypto: create ciphers on demand

block/crypto: create ciphers on demand

Ciphers are pre-allocated by qcrypto_block_init_cipher() depending on
the given number of threads. The -device
virtio-blk-pci,iothread-vq-mapping= feature allows users to assign
multiple IOThreads to a virtio-blk device, but the association between
the virtio-blk device and the block driver happens after the block
driver is already open.

When the number of threads given to qcrypto_block_init_cipher() is
smaller than the actual number of threads at runtime, the
block->n_free_ciphers > 0 assertion in qcrypto_block_pop_cipher() can
fail.

Get rid of qcrypto_block_init_cipher() n_thread's argument and allocate
ciphers on demand.

Reported-by: Qing Wang <qinwang@redhat.com>
Buglink: https://issues.redhat.com/browse/RHEL-36159
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20240527155851.892885-2-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>