[PATCH 6/8] block: sed-opal: split generation of bytestring header and content

[Jonas Rabenstein]

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.rabenst...@studium.uni-erlangen.de>
---
 block/sed-opal.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/block/sed-opal.c b/block/sed-opal.c
index f7925e6f607c..f169e621279a 100644
--- a/block/sed-opal.c
+++ b/block/sed-opal.c
@@ -584,14 +584,11 @@ static void add_token_u64(int *err, struct opal_dev *cmd, 
u64 number)
        }
 }
 
-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;
@@ -600,17 +597,27 @@ 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