crypto: crc32 - don't unnecessarily register arch algorithms

Instead of registering the crc32-$arch and crc32c-$arch algorithms if
the arch-specific code was built, only register them when that code was
built *and* is not falling back to the base implementation at runtime.

This avoids confusing users like btrfs which checks the shash driver
name to determine whether it is crc32c-generic.

(It would also make sense to change btrfs to test the crc32_optimization
flags itself, so that it doesn't have to use the weird hack of parsing
the driver name.  This change still makes sense either way though.)

Reviewed-by: Ard Biesheuvel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Eric Biggers <[email protected]>

Author: ebiggers

crypto/crc32_generic.c

@@ -157,15 +157,19 @@ static struct shash_alg algs[] = {{
 	.base.cra_init		= crc32_cra_init,
 }};
 
+static int num_algs;
+
 static int __init crc32_mod_init(void)
 {
 	/* register the arch flavor only if it differs from the generic one */
-	return crypto_register_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH));
+	num_algs = 1 + ((crc32_optimizations() & CRC32_LE_OPTIMIZATION) != 0);
+
+	return crypto_register_shashes(algs, num_algs);
 }
 
 static void __exit crc32_mod_fini(void)
 {
-	crypto_unregister_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH));
+	crypto_unregister_shashes(algs, num_algs);
 }
 
 subsys_initcall(crc32_mod_init);

crypto/crc32c_generic.c

@@ -197,15 +197,19 @@ static struct shash_alg algs[] = {{
 	.base.cra_init		= crc32c_cra_init,
 }};
 
+static int num_algs;
+
 static int __init crc32c_mod_init(void)
 {
 	/* register the arch flavor only if it differs from the generic one */
-	return crypto_register_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH));
+	num_algs = 1 + ((crc32_optimizations() & CRC32C_OPTIMIZATION) != 0);
+
+	return crypto_register_shashes(algs, num_algs);
 }
 
 static void __exit crc32c_mod_fini(void)
 {
-	crypto_unregister_shashes(algs, 1 + IS_ENABLED(CONFIG_CRC32_ARCH));
+	crypto_unregister_shashes(algs, num_algs);
 }
 
 subsys_initcall(crc32c_mod_init);