linux-kernel - [PATCH] fpga: bridge: return errors in the show() method of the "state" attribute

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Message-Id: <20230125140622.176870-1-marpagan@redhat.com>
Date:   Wed, 25 Jan 2023 15:06:22 +0100
From:   Marco Pagani <marpagan@...hat.com>
To:     Moritz Fischer <mdf@...nel.org>, Wu Hao <hao.wu@...el.com>,
        Xu Yilun <yilun.xu@...el.com>, Tom Rix <trix@...hat.com>
Cc:     Marco Pagani <marpagan@...hat.com>, linux-fpga@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] fpga: bridge: return errors in the show() method of the "state" attribute

This patch changes the show() method of the "state" sysfs attribute to
propagate errors returned by the enable_show() op. In this way,
userspace can distinguish between when the bridge is actually "enabled"
(i.e., allowing signals) or "disabled" (i.e., gating signals), or when
there is an error.

Currently, enable_show() returns an integer representing the bridge's
state (enabled or disabled) or an error code. However, this integer
value is interpreted in state_show() as a bool, resulting in the method
printing "enabled" (i.e., the bridge allows signals to pass), without
propagating the error, even when enable_show() returns an error code.

Thanks

Signed-off-by: Marco Pagani <marpagan@...hat.com>
---
 drivers/fpga/fpga-bridge.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/fpga/fpga-bridge.c b/drivers/fpga/fpga-bridge.c
index 727704431f61..5cd40acab5bf 100644
--- a/drivers/fpga/fpga-bridge.c
+++ b/drivers/fpga/fpga-bridge.c
@@ -293,12 +293,15 @@ static ssize_t state_show(struct device *dev,
 			  struct device_attribute *attr, char *buf)
 {
 	struct fpga_bridge *bridge = to_fpga_bridge(dev);
-	int enable = 1;
+	int state = 1;

-	if (bridge->br_ops && bridge->br_ops->enable_show)
-		enable = bridge->br_ops->enable_show(bridge);
+	if (bridge->br_ops && bridge->br_ops->enable_show) {
+		state = bridge->br_ops->enable_show(bridge);
+		if (state < 0)
+			return state;
+	}

-	return sprintf(buf, "%s\n", enable ? "enabled" : "disabled");
+	return sysfs_emit(buf, "%s\n", state ? "enabled" : "disabled");
 }

 static DEVICE_ATTR_RO(name);
-- 
2.39.1