block: sed-opal: unify space check in add_token_*

All add_token_* functions have a common set of conditions that have to
be checked. Use a common function for those checks in order to avoid
different behaviour as well as code duplication.
Acked-by: Jon Derrick <jonathan.derrick@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Scott Bauer <sbauer@plzdonthack.me>
Co-authored-by: David Kozub <zub@linux.fjfi.cvut.cz>
Signed-off-by: Jonas Rabenstein <jonas.rabenstein@studium.uni-erlangen.de>
Signed-off-by: David Kozub <zub@linux.fjfi.cvut.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/sed-opal.c

@@ -510,15 +510,24 @@ static int opal_discovery0(struct opal_dev *dev, void *data)
 	return opal_discovery0_end(dev);
 }
 
-static void add_token_u8(int *err, struct opal_dev *cmd, u8 tok)
+static bool can_add(int *err, struct opal_dev *cmd, size_t len)
 {
 	if (*err)
-		return;
-	if (cmd->pos >= IO_BUFFER_LENGTH - 1) {
-		pr_debug("Error adding u8: end of buffer.\n");
+		return false;
+
+	if (len > IO_BUFFER_LENGTH || cmd->pos > IO_BUFFER_LENGTH - len) {
+		pr_debug("Error adding %zu bytes: end of buffer.\n", len);
 		*err = -ERANGE;
-		return;
+		return false;
 	}
+
+	return true;
+}
+
+static void add_token_u8(int *err, struct opal_dev *cmd, u8 tok)
+{
+	if (!can_add(err, cmd, 1))
+		return;
 	cmd->cmd[cmd->pos++] = tok;
 }
 
@@ -562,9 +571,8 @@ static void add_token_u64(int *err, struct opal_dev *cmd, u64 number)
 	msb = fls64(number);
 	len = DIV_ROUND_UP(msb, 8);
 
-	if (cmd->pos >= IO_BUFFER_LENGTH - len - 1) {
+	if (!can_add(err, cmd, len + 1)) {
 		pr_debug("Error adding u64: end of buffer.\n");
-		*err = -ERANGE;
 		return;
 	}
 	add_short_atom_header(cmd, false, false, len);
@@ -586,9 +594,8 @@ static void add_token_bytestring(int *err, struct opal_dev *cmd,
 		is_short_atom = false;
 	}
 
-	if (len >= IO_BUFFER_LENGTH - cmd->pos - header_len) {
+	if (!can_add(err, cmd, header_len + len)) {
 		pr_debug("Error adding bytestring: end of buffer.\n");
-		*err = -ERANGE;
 		return;
 	}