Hi,
I have written a module that implements GCM algorithm for LKCF (by calling dedicated hardware).
I would like to understand how the priority mechanism works in order to be sure that my module will be selected when I need to. At the moment it seems it is always used, which is great but I'd like to understand why :)
Here is the crypto_alg structure I am using to register the algorithm:
static struct crypto_alg aead_authenc_aes_gcm = {
.cra_name = "rfc4106(gcm(aes))",
.cra_driver_name = "icp_aead",
.cra_priority = ICP_AES_ASYNC_PRIORITY, /* 3001*/
.cra_flags = CRYPTO_ALG_TYPE_AEAD|CRYPTO_ALG_GENIV|CRYPTO_ALG_ASYNC,
.cra_blocksize = AES_BLOCK_SIZE /*16*/,
.cra_ctxsize = 0,
.cra_type = &crypto_aead_type,
.cra_module = THIS_MODULE,
.cra_list = LIST_HEAD_INIT(aead_authenc_aes_gcm.cra_list),
.cra_exit = aead_auth_exit,
.cra_u = {
.aead = {
.ivsize = AES_GCM_IV_SIZE, /*8*/
.maxauthsize = AES_GCM_AUTH_TAG_LEN, /*16*/
.setkey = setkey_aes_gcm,
.setauthsize = qat_setauthsize,
.encrypt = encrypt_aes_gcm,
.decrypt = decrypt_aes_gcm,
.givencrypt = geniv_encrypt_aes_gcm,
.givdecrypt = geniv_decrypt_aes_gcm,
}
}
};
The algorithm is registered by calling crypto_register_alg in the module_init function.
It seems that my module is always used regardless of the value of the priority (I tried to set it to 0 or even to -1).
I have also tried to load the default gcm kernel module before (or after) mine but my module is selected in both cases.
I have checked in the kernel code and I did not see any location where cra_priority is used.
So my questions are:
-What is this variable used for?
-If there are multiple implementations of the same algorithm, how is one version chosen as opposed to another one?
I guess that the reason is that an asynchronous version always has a higher priority than a synchronous one. Is that correct?
Thanks
Mario
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