[PATCH v2 ethtool] qsfp: Better handling of Page 03h netlink read failure

["Krzysztof Olędzki" <ole@ans.pl>]

When dumping the EEPROM contents of a QSFP transceiver module, ethtool
will only ask the kernel to retrieve Upper Page 03h if the module
advertised it as supported.

However, some kernel drivers like mlx4 are currently unable to provide
the page, resulting in the kernel returning an error. Since Upper Page
03h is optional, do not treat the error as fatal. Instead, print an
error message and allow ethtool to continue and parse / print the
contents of the other pages.

Also, clarify potentially cryptic "netlink error: Invalid argument" message.

Before:
 # ethtool -m eth3
 netlink error: Invalid argument

After:
 # ethtool -m eth3
 netlink error: Invalid argument
 Failed to read Upper Page 03h, driver error?
         Identifier                                : 0x0d (QSFP+)
         Extended identifier                       : 0x00
 (...)

Fixes: 25b64c66f58d ("ethtool: Add netlink handler for getmodule (-m)")

Signed-off-by: Krzysztof Piotr Oledzki <ole@ans.pl>
---
 qsfp.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/qsfp.c b/qsfp.c
index a2921fb..a3a919d 100644
--- a/qsfp.c
+++ b/qsfp.c
@@ -1038,8 +1038,15 @@ sff8636_memory_map_init_pages(struct cmd_context *ctx,
 
 	sff8636_request_init(&request, 0x3, SFF8636_PAGE_SIZE);
 	ret = nl_get_eeprom_page(ctx, &request);
-	if (ret < 0)
-		return ret;
+	if (ret < 0) {
+		/* Page 03h is not available due to a bug in the driver.
+		 * This is a non-fatal error and sff8636_dom_parse()
+		 * handles this correctly.
+		 */
+		fprintf(stderr, "Failed to read Upper Page 03h, driver error?\n");
+		return 0;
+	}
+
 	map->page_03h = request.data - SFF8636_PAGE_SIZE;
 
 	return 0;
-- 
2.45.2