CRYPTO_TFM_REQ_MASK and CRYPTO_TFM_RES_MASK

[Dimitrios Siganos <dimitris@siganos.org>]

Hi,

Could someone explain what the masks CRYPTO_TFM_REQ_MASK and 
CRYPTO_TFM_RES_MASK do and why they must be manipulated before and after 
crypto_cipher_setkey(...)?

Here is an example use (from crypto_pcbc_setkey):
    crypto_cipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
    crypto_cipher_set_flags(child, crypto_tfm_get_flags(parent) &
                CRYPTO_TFM_REQ_MASK);
    err = crypto_cipher_setkey(child, key, keylen);
    crypto_tfm_set_flags(parent, crypto_cipher_get_flags(child) &
                 CRYPTO_TFM_RES_MASK);

It would be very useful if someone added some comments to these 
definitions (found in linux/crypto.h):

/*
 * Transform masks and values (for crt_flags).
 */
#define CRYPTO_TFM_REQ_MASK        0x000fff00
#define CRYPTO_TFM_RES_MASK        0xfff00000

#define CRYPTO_TFM_REQ_WEAK_KEY        0x00000100
#define CRYPTO_TFM_REQ_MAY_SLEEP    0x00000200
#define CRYPTO_TFM_REQ_MAY_BACKLOG    0x00000400
#define CRYPTO_TFM_RES_WEAK_KEY        0x00100000
#define CRYPTO_TFM_RES_BAD_KEY_LEN       0x00200000
#define CRYPTO_TFM_RES_BAD_KEY_SCHED     0x00400000
#define CRYPTO_TFM_RES_BAD_BLOCK_LEN     0x00800000
#define CRYPTO_TFM_RES_BAD_FLAGS     0x01000000

Thanks,
Dimitris