linux-kernel - [PATCH v2 06/11] block: sed-opal: split generation of bytestring header and content

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Message-Id: <0f5fe62576e70de12515e323ca5c0a45ef92832d.1521482296.git.jonas.rabenstein@studium.uni-erlangen.de>
Date:   Mon, 19 Mar 2018 19:36:48 +0100
From:   Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>
To:     Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>,
        Scott Bauer <scott.bauer@...el.com>,
        Jonathan Derrick <jonathan.derrick@...el.com>,
        Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: [PATCH v2 06/11] block: sed-opal: split generation of bytestring header and content

Split the header generation from the (normal) memcpy part if a
bytestring is copied into the command buffer. This allows in-place
generation of the bytestring content. For example, copy_from_user may be
used without an intermediate buffer.

Signed-off-by: Jonas Rabenstein <jonas.rabenstein@...dium.uni-erlangen.de>

diff --git a/block/sed-opal.c b/block/sed-opal.c
index 9b6f14e7aeb1..fc10f81d4892 100644
--- a/block/sed-opal.c
+++ b/block/sed-opal.c
@@ -581,14 +581,11 @@ static void add_token_u64(int *err, struct opal_dev *cmd, u64 number)
 		add_token_u8(err, cmd, number >> (len * 8));
 }
 
-static void add_token_bytestring(int *err, struct opal_dev *cmd,
-				 const u8 *bytestring, size_t len)
+static u8 *add_bytestring_header(int *err, struct opal_dev *cmd, size_t len)
 {
 	size_t header_len = 1;
 	bool is_short_atom = true;
-
-	if (*err)
-		return;
+	char *start;
 
 	if (len & ~SHORT_ATOM_LEN_MASK) {
 		header_len = 2;
@@ -597,17 +594,27 @@ static void add_token_bytestring(int *err, struct opal_dev *cmd,
 
 	if (!can_add(err, cmd, header_len + len)) {
 		pr_debug("Error adding bytestring: end of buffer.\n");
-		return;
+		return NULL;
 	}
 
 	if (is_short_atom)
 		add_short_atom_header(cmd, true, false, len);
 	else
 		add_medium_atom_header(cmd, true, false, len);
-
-	memcpy(&cmd->cmd[cmd->pos], bytestring, len);
+	start = &cmd->cmd[cmd->pos];
 	cmd->pos += len;
+	return start;
+}
 
+static void add_token_bytestring(int *err, struct opal_dev *cmd,
+				 const u8 *bytestring, size_t len)
+{
+	u8 *start;
+
+	start = add_bytestring_header(err, cmd, len);
+	if (!start)
+		return;
+	memcpy(start, bytestring, len);
 }
 
 static int build_locking_range(u8 *buffer, size_t length, u8 lr)
-- 
2.16.1