opencrypto: Add a routine to copy a crypto buffer cursor

This was useful in converting armv8crypto to use buffer cursors.  There
are some cases where one wants to make two passes over data, and this
provides a way to "reset" a cursor.

Reviewed by:	jhb
MFC after:	1 month
Differential Revision:	https://reviews.freebsd.org/D28949

2 files changed, 19 insertions, 1 deletions

diff --git a/share/man/man9/crypto_buffer.9 b/share/man/man9/crypto_buffer.9
index c6911d3bb1c9..87cdf53b1abd 100644
--- a/share/man/man9/crypto_buffer.9
+++ b/share/man/man9/crypto_buffer.9
@@ -30,7 +30,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd June 16, 2021
+.Dd Feburary 11, 2022
 .Dt CRYPTO_BUFFER 9
 .Os
 .Sh NAME
@@ -95,6 +95,11 @@
 .Fc
 .Ft void *
 .Fn crypto_cursor_segment "struct crypto_buffer_cursor *cc" "size_t *len"
+.Ft void
+.Fo crypto_cursor_copy
+.Fa "const struct crypto_buffer_cursor *fromc"
+.Fa "struct crypto_buffer_cursor *toc"
+.Fc
 .Ft bool
 .Fn CRYPTO_HAS_OUTPUT_BUFFER "struct cryptop *crp"
 .Sh DESCRIPTION
@@ -315,6 +320,12 @@ returns the length of a buffer in bytes.
 .Fn crypto_cursor_seglen
 returns the length in bytes of a contiguous segment.
 .Pp
+.Fn crypto_cursor_copy
+makes a deep copy of the cursor
+.Fa fromc .
+The two copies do not share any state and can thus be used
+independently.
+.Pp
 .Fn CRYPTO_HAS_OUTPUT_BUFFER
 returns true if the request uses a separate output buffer.
 .Sh SEE ALSO
diff --git a/sys/opencrypto/cryptodev.h b/sys/opencrypto/cryptodev.h
index 3eef1aada2a7..3a0022996a3c 100644
--- a/sys/opencrypto/cryptodev.h
+++ b/sys/opencrypto/cryptodev.h
@@ -686,6 +686,13 @@ void	crypto_cursor_copydata_noadv(struct crypto_buffer_cursor *cc, int size,
 	    void *vdst);
 
 static __inline void
+crypto_cursor_copy(const struct crypto_buffer_cursor *fromc,
+    struct crypto_buffer_cursor *toc)
+{
+	memcpy(toc, fromc, sizeof(*toc));
+}
+
+static __inline void
 crypto_read_iv(struct cryptop *crp, void *iv)
 {
 	const struct crypto_session_params *csp;