[PATCH v4 04/19] crypto: crc32 - don't unnecessarily register arch algorithms

[Eric Biggers <ebiggers@xxxxxxxxxx>]

From: Eric Biggers <ebiggers@xxxxxxxxxx>

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 <ardb@xxxxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
 crypto/crc32_generic.c  | 8 ++++++--
 crypto/crc32c_generic.c | 8 ++++++--
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/crypto/crc32_generic.c b/crypto/crc32_generic.c
index cc064ea8240e..783a30b27398 100644
--- a/crypto/crc32_generic.c
+++ b/crypto/crc32_generic.c
@@ -155,19 +155,23 @@ static struct shash_alg algs[] = {{
 	.base.cra_ctxsize	= sizeof(u32),
 	.base.cra_module	= THIS_MODULE,
 	.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);
 module_exit(crc32_mod_fini);
 
diff --git a/crypto/crc32c_generic.c b/crypto/crc32c_generic.c
index 04b03d825cf4..985da981d6e2 100644
--- a/crypto/crc32c_generic.c
+++ b/crypto/crc32c_generic.c
@@ -195,19 +195,23 @@ static struct shash_alg algs[] = {{
 	.base.cra_ctxsize	= sizeof(struct chksum_ctx),
 	.base.cra_module	= THIS_MODULE,
 	.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);
 module_exit(crc32c_mod_fini);
 
-- 
2.47.1