[PATCH 4/4] hwrng: core - use sysfs_emit_at in rng_available_show

[Thorsten Blum <thorsten.blum@linux.dev>]

Replace strlcat() with sysfs_emit_at() in rng_available_show() and add
'int len' to keep track of the number of bytes written. sysfs_emit_at()
is preferred for formatting sysfs output because it provides safer
bounds checking.

Inline mutex_lock_interruptible() and drop the now-unused local error
variable. Remove the unnecessary 'buf' NUL initialization. Return 'len'
directly instead of strlen(buf).

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 drivers/char/hw_random/core.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index f8f7a2ee73c1..1d1ea4ebde31 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -26,6 +26,7 @@
 #include <linux/sched/signal.h>
 #include <linux/slab.h>
 #include <linux/string.h>
+#include <linux/sysfs.h>
 #include <linux/uaccess.h>
 #include <linux/workqueue.h>
 
@@ -415,21 +416,17 @@ static ssize_t rng_available_show(struct device *dev,
 				  struct device_attribute *attr,
 				  char *buf)
 {
-	int err;
 	struct hwrng *rng;
+	int len = 0;
 
-	err = mutex_lock_interruptible(&rng_mutex);
-	if (err)
+	if (mutex_lock_interruptible(&rng_mutex))
 		return -ERESTARTSYS;
-	buf[0] = '\0';
-	list_for_each_entry(rng, &rng_list, list) {
-		strlcat(buf, rng->name, PAGE_SIZE);
-		strlcat(buf, " ", PAGE_SIZE);
-	}
-	strlcat(buf, "none\n", PAGE_SIZE);
+	list_for_each_entry(rng, &rng_list, list)
+		len += sysfs_emit_at(buf, len, "%s ", rng->name);
+	len += sysfs_emit_at(buf, len, "none\n");
 	mutex_unlock(&rng_mutex);
 
-	return strlen(buf);
+	return len;
 }
 
 static ssize_t rng_selected_show(struct device *dev,