[PATCH v2 3/3] include/crypto: clarify @result/@result_len for hash/hmac APIs

["Daniel P. Berrangé" <berrange@redhat.com>]

The @result parameter passed to hash/hmac APIs may either contain
a pre-allocated buffer, or a buffer can be allocated on the fly.
Clarify these two different usage models in the API docs.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/crypto/hash.h | 30 +++++++++++++++++++++++-------
 include/crypto/hmac.h | 17 ++++++++++++-----
 2 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index b791ca92a4..317bf9ecde 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h
@@ -98,11 +98,18 @@ int qcrypto_hash_bytesv(QCryptoHashAlgo alg,
  * @errp: pointer to a NULL-initialized error object
  *
  * Computes the hash across all the memory region
- * @buf of length @len. The @result pointer will be
- * filled with raw bytes representing the computed
- * hash, which will have length @resultlen. The
- * memory pointer in @result must be released
- * with a call to g_free() when no longer required.
+ * @buf of length @len.
+ *
+ * If @result_len is set to a non-zero value by the caller, then
+ * @result must hold a pointer that is @result_len in size, and
+ * @result_len match the size of the hash output. The digest will
+ * be written into @result.
+ *
+ * If @result_len is set to zero, then this function will allocate
+ * a buffer to hold the hash output digest, storing a pointer to
+ * the buffer in @result, and setting @result_len to its size.
+ * The memory referenced in @result must be released with a call
+ * to g_free() when no longer required by the caller.
  *
  * Returns: 0 on success, -1 on error
  */
@@ -215,8 +222,17 @@ int qcrypto_hash_finalize_base64(QCryptoHash *hash,
  *
  * Computes the hash from the given hash object. Hash object
  * is expected to have it's data updated from the qcrypto_hash_update function.
- * The memory pointer in @result must be released with a call to g_free()
- * when no longer required.
+ *
+ * If @result_len is set to a non-zero value by the caller, then
+ * @result must hold a pointer that is @result_len in size, and
+ * @result_len match the size of the hash output. The digest will
+ * be written into @result.
+ *
+ * If @result_len is set to zero, then this function will allocate
+ * a buffer to hold the hash output digest, storing a pointer to
+ * the buffer in @result, and setting @result_len to its size.
+ * The memory referenced in @result must be released with a call
+ * to g_free() when no longer required by the caller.
  *
  * Returns: 0 on success, -1 on error
  */
diff --git a/include/crypto/hmac.h b/include/crypto/hmac.h
index c69a0dfab3..aaff95f7db 100644
--- a/include/crypto/hmac.h
+++ b/include/crypto/hmac.h
@@ -103,11 +103,18 @@ int qcrypto_hmac_bytesv(QCryptoHmac *hmac,
  * @errp: pointer to a NULL-initialized error object
  *
  * Computes the hmac across all the memory region
- * @buf of length @len. The @result pointer will be
- * filled with raw bytes representing the computed
- * hmac, which will have length @resultlen. The
- * memory pointer in @result must be released
- * with a call to g_free() when no longer required.
+ * @buf of length @len.
+ *
+ * If @result_len is set to a non-zero value by the caller, then
+ * @result must hold a pointer that is @result_len in size, and
+ * @result_len match the size of the hash output. The digest will
+ * be written into @result.
+ *
+ * If @result_len is set to zero, then this function will allocate
+ * a buffer to hold the hash output digest, storing a pointer to
+ * the buffer in @result, and setting @result_len to its size.
+ * The memory referenced in @result must be released with a call
+ * to g_free() when no longer required by the caller.
  *
  * Returns:
  *  0 on success, -1 on error
-- 
2.46.0