nl80211: Missing sysctl flags aren't fatal

The relevant flags were only added in Linux 4.6, so we shouldn't
complain because they're missing. Also, they're always missing if a
device is being removed (e.g., 'iw dev wlan0 del', or if the device is
in the process of resetting itself). So kill those 2 birds with 1 stone:
if we can't find the file, just silently skip it.

Also, we probably should *actually* propagate the error if we had a
write failure.

Signed-off-by: Brian Norris <briannorris@chromium.org>

diff --git a/src/drivers/driver_nl80211.c b/src/drivers/driver_nl80211.c
index 8ad1072a4b83e602447c3a659a35ef9b080cba28..7ed1878ad93b973afaa30c8d3b7b327ee668af48 100644 (file)
--- a/src/drivers/driver_nl80211.c
+++ b/src/drivers/driver_nl80211.c
@@ -10746,22 +10746,37 @@ static int nl80211_write_to_file(const char *name, unsigned int val)
 {
        int fd, len;
        char tmp[128];
+       int ret = 0;
 
        fd = open(name, O_RDWR);
        if (fd < 0) {
-               wpa_printf(MSG_ERROR, "nl80211: Failed to open %s: %s",
+               int level;
+               /*
+                * Flags may not exist on older kernels, or while we're tearing
+                * down a disappearing device.
+                */
+               if (errno == ENOENT) {
+                       ret = 0;
+                       level = MSG_DEBUG;
+               } else {
+                       ret = -1;
+                       level = MSG_ERROR;
+               }
+               wpa_printf(level, "nl80211: Failed to open %s: %s",
                           name, strerror(errno));
-               return fd;
+               return ret;
        }
 
        len = os_snprintf(tmp, sizeof(tmp), "%u\n", val);
        len = write(fd, tmp, len);
-       if (len < 0)
+       if (len < 0) {
+               ret = -1;
                wpa_printf(MSG_ERROR, "nl80211: Failed to write to %s: %s",
                           name, strerror(errno));
+       }
        close(fd);
 
-       return 0;
+       return ret;
 }