[PATCH net-next 2/3] eth: fbnic: Update fbnic_tlv_attr_get_string() to work like nla_strscpy()

[Lee Trager <lee@trager.us>]

Allow fbnic_tlv_attr_get_string() to return an error code. In the event the
source mailbox attribute is missing return -EINVAL. Like nla_strscpy() return
-E2BIG when the source string is larger than the destination string. In this
case the amount of data copied is equal to dstsize.

Signed-off-by: Lee Trager <lee@trager.us>
---
 drivers/net/ethernet/meta/fbnic/fbnic_tlv.c | 39 ++++++++++++++++-----
 drivers/net/ethernet/meta/fbnic/fbnic_tlv.h |  4 +--
 2 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/meta/fbnic/fbnic_tlv.c b/drivers/net/ethernet/meta/fbnic/fbnic_tlv.c
index 2a174ab062a3..400fb6c80053 100644
--- a/drivers/net/ethernet/meta/fbnic/fbnic_tlv.c
+++ b/drivers/net/ethernet/meta/fbnic/fbnic_tlv.c
@@ -233,19 +233,40 @@ s64 fbnic_tlv_attr_get_signed(struct fbnic_tlv_msg *attr)
 /**
  * fbnic_tlv_attr_get_string - Retrieve string value from result
  * @attr: Attribute to retrieve data from
- * @str: Pointer to an allocated string to store the data
- * @max_size: The maximum size which can be in str
+ * @dst: Pointer to an allocated string to store the data
+ * @dstsize: The maximum size which can be in dst
  *
- * Return: the size of the string read from firmware
+ * Return: the size of the string read from firmware or negative error.
  **/
-size_t fbnic_tlv_attr_get_string(struct fbnic_tlv_msg *attr, char *str,
-				 size_t max_size)
+ssize_t fbnic_tlv_attr_get_string(struct fbnic_tlv_msg *attr, char *dst,
+				  size_t dstsize)
 {
-	max_size = min_t(size_t, max_size,
-			 (le16_to_cpu(attr->hdr.len) * 4) - sizeof(*attr));
-	memcpy(str, &attr->value, max_size);
+	size_t srclen, len;
+	ssize_t ret;

-	return max_size;
+	if (!attr)
+		return -EINVAL;
+
+	if (dstsize == 0)
+		return -E2BIG;
+
+	srclen = le16_to_cpu(attr->hdr.len) - sizeof(*attr);
+	if (srclen > 0 && attr->value[srclen - 1] == '\0')
+		srclen--;
+
+	if (srclen >= dstsize) {
+		len = dstsize - 1;
+		ret = -E2BIG;
+	} else {
+		len = srclen;
+		ret = len;
+	}
+
+	memcpy(dst, &attr->value, len);
+	/* Zero pad end of dst. */
+	memset(dst + len, 0, dstsize - len);
+
+	return ret;
 }

 /**
diff --git a/drivers/net/ethernet/meta/fbnic/fbnic_tlv.h b/drivers/net/ethernet/meta/fbnic/fbnic_tlv.h
index 67300ab44353..b29ed2649585 100644
--- a/drivers/net/ethernet/meta/fbnic/fbnic_tlv.h
+++ b/drivers/net/ethernet/meta/fbnic/fbnic_tlv.h
@@ -116,8 +116,8 @@ static inline bool fbnic_tlv_attr_get_bool(struct fbnic_tlv_msg *attr)

 u64 fbnic_tlv_attr_get_unsigned(struct fbnic_tlv_msg *attr);
 s64 fbnic_tlv_attr_get_signed(struct fbnic_tlv_msg *attr);
-size_t fbnic_tlv_attr_get_string(struct fbnic_tlv_msg *attr, char *str,
-				 size_t max_size);
+ssize_t fbnic_tlv_attr_get_string(struct fbnic_tlv_msg *attr, char *dst,
+				  size_t dstsize);

 #define get_unsigned_result(id, location) \
 do { \
--
2.43.5