liblxqt/liblxqt-0.13.0-backlight.patch

See: https://github.com/lxqt/liblxqt/pull/148

From a4671083ad7277288fa2a17b90efc11439088df2 Mon Sep 17 00:00:00 2001
From: Matthias Gerstner <matthias.gerstner@suse.de>
Date: Wed, 13 Jun 2018 16:31:15 +0200
Subject: [PATCH 1/8] lxqtbacklight: centralize fopen() and perform path
 handling with length checks

---
 .../linux_backend/driver/libbacklight_backend.c    | 47 ++++++++++++++--------
 .../linux_backend/driver/lxqtbacklight_backend.c   | 14 ++-----
 2 files changed, 33 insertions(+), 28 deletions(-)

diff --git a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
index 13689ef..4d90c20 100644
--- a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
@@ -55,6 +55,7 @@
  *    in order to write in /sys/class/backlight/driver/brightness file.
  *******************************************************************************/
 
+#include <limits.h>
 #include <stdio.h>
 #include <dirent.h>
 #include <errno.h>
@@ -67,6 +68,7 @@
 #define True 1
 #define False 0
 
+static FILE* open_driver_file(const char *path, const char *driver, const char *mode);
 static int read_backlight(char *driver);
 static int read_max_backlight(char *driver);
 static int read_bl_power(char *driver);
@@ -114,13 +116,10 @@ int lxqt_backlight_is_backlight_off()
     return bl_power;
 }
 
-static int read_int(char *path)
+static int read_int(const char *tpl, const char *driver)
 {
-    FILE *in = fopen(path, "r");
+    FILE *in = open_driver_file(tpl, driver, "r");
     if( in == NULL ) {
-        char buffer[1024];
-        sprintf(buffer, "Couldn't open %s", path);
-        perror(buffer);
         return -1;
     }
     int value;
@@ -132,25 +131,40 @@ static int read_int(char *path)
     return value;
 }
 
+static FILE* open_driver_file(const char *tpl, const char *driver, const char *mode)
+{
+    char path[PATH_MAX];
+    int res;
+
+    res = snprintf(path, PATH_MAX, tpl, driver);
+
+    if( res <= 0 || res >= PATH_MAX ) {
+        path[0] = '\0';
+        return NULL;
+    }
+
+    FILE *ret = fopen(path, mode);
+
+    if( ret == NULL ) {
+        fprintf(stderr, "Couldn't open %s: %s\n", path, strerror(errno));
+    }
+
+    return ret;
+}
+
 static int read_backlight(char *driver)
 {
-    char path[1024];
-    sprintf(path, "/sys/class/backlight/%s/actual_brightness", driver);
-    return read_int(path);
+    return read_int("/sys/class/backlight/%s/actual_brightness", driver);
 }
 
 static int read_max_backlight(char *driver)
 {
-    char path[1024];
-    sprintf(path, "/sys/class/backlight/%s/max_brightness", driver);
-    return read_int(path);
+    return read_int("/sys/class/backlight/%s/max_brightness", driver);
 }
 
 static int read_bl_power(char *driver)
 {
-    char path[1024];
-    sprintf(path, "/sys/class/backlight/%s/bl_power", driver);
-    return read_int(path);
+    return read_int("/sys/class/backlight/%s/bl_power", driver);
 }
 
 typedef enum {FIRMWARE, PLATFORM, RAW, OTHER, N_BACKLIGHT} BackligthTypes;
@@ -163,7 +177,7 @@ char *lxqt_backlight_backend_get_driver()
     char *drivers[N_BACKLIGHT];
     char *driver;
     int n;
-    char path[1024], type[1024];
+    char type[1024];
     
     for(n=0;n<N_BACKLIGHT;n++)
         drivers[n] = NULL;
@@ -179,8 +193,7 @@ char *lxqt_backlight_backend_get_driver()
             if( !strcmp(dp->d_name, ".") || !strcmp(dp->d_name, "..") )
                 continue;
             driver = dp->d_name;
-            sprintf(path, "/sys/class/backlight/%s/type", driver);
-            FILE *in = fopen(path, "r");
+            FILE *in = open_driver_file("/sys/class/backlight/%s/type", driver, "r");
             if( in == NULL )
                 continue;
             int ok = fscanf(in, "%s", type);
diff --git a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
index 9586485..45c9281 100644
--- a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
@@ -35,14 +35,10 @@
  */
 static void set_bl_power(char *driver, int value)
 {
-    char path[1024];
-    sprintf(path, "/sys/class/backlight/%s/bl_power", driver);
-    FILE *out = fopen(path, "w");
+    FILE *out = open_driver_file("/sys/class/backlight/%s/bl_power", driver, "w");
     if( out != NULL ) {
         fprintf(out, "%d", value);
         fclose(out);
-    } else {
-        perror("Couldn't open /sys/class/backlight/driver/bl_power");
     }
 }
 
@@ -50,14 +46,10 @@ static void set_bl_power(char *driver, int value)
 static void set_backlight(char *driver, int value)
 {
     if(value>0) {
-        char path[1024];
-        sprintf(path, "/sys/class/backlight/%s/brightness", driver);
-        FILE *out = fopen(path, "w");
+        FILE *out = open_driver_file("/sys/class/backlight/%s/brightness", driver, "w");
         if( out != NULL ) {
             fprintf(out, "%d", value);
             fclose(out);
-        } else {
-            perror("Couldn't open /sys/class/backlight/driver/brightness");
         }
         if(read_bl_power(driver) > 0)
             set_bl_power(driver, 0);
@@ -247,4 +239,4 @@ int main(int argc, char *argv[])
     change_blacklight(value, value_percent_ok);
 
     return 0;
-}
\ No newline at end of file
+}

From 318f85b2aca43ed6c9b4f6099f3d476bb8b9e1c2 Mon Sep 17 00:00:00 2001
From: Matthias Gerstner <matthias.gerstner@suse.de>
Date: Wed, 13 Jun 2018 16:36:41 +0200
Subject: [PATCH 2/8] lxqtbacklight: apply maximum string length to fscanf to
 prevent overflow

---
 lxqtbacklight/linux_backend/driver/libbacklight_backend.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
index 4d90c20..c7ce7ab 100644
--- a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
@@ -196,7 +196,8 @@ char *lxqt_backlight_backend_get_driver()
             FILE *in = open_driver_file("/sys/class/backlight/%s/type", driver, "r");
             if( in == NULL )
                 continue;
-            int ok = fscanf(in, "%s", type);
+            // the maximum field width does not include '\0'!
+            int ok = fscanf(in, "%1023s", type);
             fclose(in);
             if( ok != EOF ) {
                 // firmware control should be preferred to platform control should be preferred to raw control.

From 628dbd33fcaf93b79334572782991ac8d4362f14 Mon Sep 17 00:00:00 2001
From: Matthias Gerstner <matthias.gerstner@suse.de>
Date: Wed, 13 Jun 2018 16:49:07 +0200
Subject: [PATCH 3/8] lxqtbacklight: removed useless commented out code

---
 .../linux_backend/driver/lxqtbacklight_backend.c   | 34 ----------------------
 1 file changed, 34 deletions(-)

diff --git a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
index 45c9281..3dc7d7e 100644
--- a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
@@ -58,40 +58,6 @@ static void set_backlight(char *driver, int value)
     }
 }
 
-
-// static int read_int(char *path)
-// {
-//     FILE *in = fopen(path, "r");
-//     if( in == NULL ) {
-//         char buffer[1024];
-//         sprintf(buffer, "Couldn't open %s", path);
-//         perror(buffer);
-//         return -1;
-//     }
-//     int value;
-//     int ok = fscanf(in, "%d", &value);
-//     fclose(in);
-//     if( ok == EOF ) {
-//         value = 0;
-//     }
-//     return value;
-// }
-
-
-// static int read_backlight(char *driver)
-// {
-//     char path[1024];
-//     sprintf(path, "/sys/class/backlight/%s/actual_brightness", driver);
-//     return read_int(path);
-// }
-
-// static int read_max_backlight(char *driver)
-// {
-//     char path[1024];
-//     sprintf(path, "/sys/class/backlight/%s/max_brightness", driver);
-//     return read_int(path);
-// }
-
 static char *get_driver()
 {
     return lxqt_backlight_backend_get_driver();

From 8ddd5354c6e5175d0674ff77ff7093d9b4fdba3e Mon Sep 17 00:00:00 2001
From: Matthias Gerstner <matthias.gerstner@suse.de>
Date: Wed, 13 Jun 2018 16:52:42 +0200
Subject: [PATCH 4/8] lxqtbacklight: constified char *driver, where appropriate

---
 lxqtbacklight/linux_backend/driver/libbacklight_backend.c  | 12 ++++++------
 lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c |  4 ++--
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
index c7ce7ab..bab2c48 100644
--- a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
@@ -69,9 +69,9 @@
 #define False 0
 
 static FILE* open_driver_file(const char *path, const char *driver, const char *mode);
-static int read_backlight(char *driver);
-static int read_max_backlight(char *driver);
-static int read_bl_power(char *driver);
+static int read_backlight(const char *driver);
+static int read_max_backlight(const char *driver);
+static int read_bl_power(const char *driver);
 
 int lxqt_backlight_backend_get()
 {
@@ -152,17 +152,17 @@ static FILE* open_driver_file(const char *tpl, const char *driver, const char *m
     return ret;
 }
 
-static int read_backlight(char *driver)
+static int read_backlight(const char *driver)
 {
     return read_int("/sys/class/backlight/%s/actual_brightness", driver);
 }
 
-static int read_max_backlight(char *driver)
+static int read_max_backlight(const char *driver)
 {
     return read_int("/sys/class/backlight/%s/max_brightness", driver);
 }
 
-static int read_bl_power(char *driver)
+static int read_bl_power(const char *driver)
 {
     return read_int("/sys/class/backlight/%s/bl_power", driver);
 }
diff --git a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
index 3dc7d7e..4c895ae 100644
--- a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
@@ -33,7 +33,7 @@
  * @param driver is the driver to use
  * @param value 0 turns on backlight, 4 turns off backlight
  */
-static void set_bl_power(char *driver, int value)
+static void set_bl_power(const char *driver, int value)
 {
     FILE *out = open_driver_file("/sys/class/backlight/%s/bl_power", driver, "w");
     if( out != NULL ) {
@@ -43,7 +43,7 @@ static void set_bl_power(char *driver, int value)
 }
 
 
-static void set_backlight(char *driver, int value)
+static void set_backlight(const char *driver, int value)
 {
     if(value>0) {
         FILE *out = open_driver_file("/sys/class/backlight/%s/brightness", driver, "w");

From 25114361c2e3bd60f917dde86807b4f1e72e7dc3 Mon Sep 17 00:00:00 2001
From: Matthias Gerstner <matthias.gerstner@suse.de>
Date: Wed, 13 Jun 2018 17:11:08 +0200
Subject: [PATCH 5/8] lxqtbacklight: centralized error output on empty
 backlight dir

- added missing newline to output
- also catch error in --stdin case, this could lead to a SIGSEGV on some
  libc implementations and results in trying to open
  /sys/class/backlight/(null)/max_brightness with glibc.
---
 .../linux_backend/driver/libbacklight_backend.c        | 18 +++++++++++-------
 .../linux_backend/driver/lxqtbacklight_backend.c       |  7 +++----
 2 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
index bab2c48..484e3d5 100644
--- a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
@@ -72,12 +72,12 @@ static FILE* open_driver_file(const char *path, const char *driver, const char *
 static int read_backlight(const char *driver);
 static int read_max_backlight(const char *driver);
 static int read_bl_power(const char *driver);
+static const char *sysfs_backlight_dir = "/sys/class/backlight";
 
 int lxqt_backlight_backend_get()
 {
     char *driver = lxqt_backlight_backend_get_driver();
     if( driver == NULL ) {
-        fprintf(stderr, "Error: /sys/class/backlight is empty.");
         return -1;
     }
     int value = read_backlight(driver);
@@ -89,7 +89,6 @@ int lxqt_backlight_backend_get_max()
 {
     char *driver = lxqt_backlight_backend_get_driver();
     if( driver == NULL ) {
-        fprintf(stderr, "Error: /sys/class/backlight is empty.");
         return -1;
     }
     int value = read_max_backlight(driver);
@@ -108,7 +107,6 @@ int lxqt_backlight_is_backlight_off()
 {
     char *driver = lxqt_backlight_backend_get_driver();
     if( driver == NULL ) {
-        fprintf(stderr, "Error: /sys/class/backlight is empty.");
         return -1;
     }
     int bl_power = read_bl_power(driver);
@@ -182,8 +180,8 @@ char *lxqt_backlight_backend_get_driver()
     for(n=0;n<N_BACKLIGHT;n++)
         drivers[n] = NULL;
 
-    if ((dirp = opendir("/sys/class/backlight")) == NULL) {
-        perror("Couldn't open /sys/class/backlight");
+    if ((dirp = opendir(sysfs_backlight_dir)) == NULL) {
+        fprintf(stderr, "Couldn't open %s: %s\n", sysfs_backlight_dir, strerror(errno));
         return NULL;
     }
 
@@ -216,8 +214,9 @@ char *lxqt_backlight_backend_get_driver()
 
     closedir(dirp);
 
-    if (errno != 0)
-        perror("Error reading directory");    
+    if (errno != 0) {
+        fprintf(stderr, "Error reading directory %s: %s\n", sysfs_backlight_dir, strerror(errno));
+    }
     
     driver = NULL;
     for(n=0;n<N_BACKLIGHT;n++) {
@@ -227,6 +226,11 @@ char *lxqt_backlight_backend_get_driver()
             free(drivers[n]);
     }
 
+    if( driver == NULL )
+    {
+        fprintf(stderr, "Error: %s is empty (no driver found).\n", sysfs_backlight_dir);
+    }
+
     return driver;
 }
 
diff --git a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
index 4c895ae..bcf2b9e 100644
--- a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
@@ -68,7 +68,6 @@ static void show_blacklight()
 {
     char *driver = get_driver();
     if( driver == NULL ) {
-        fprintf(stderr, "Error: /sys/class/backlight is empty.");
         return;
     }
     int max_value = read_max_backlight(driver);
@@ -81,7 +80,6 @@ static void change_blacklight(int value, int percent_ok)
 {
     char *driver = get_driver();
     if( driver == NULL ) {
-        fprintf(stderr, "Error: /sys/class/backlight is empty.");
         return;
     }
     int max_value = read_max_backlight(driver);
@@ -97,7 +95,6 @@ static void increases_blacklight()
 {
     char *driver = get_driver();
     if( driver == NULL ) {
-        fprintf(stderr, "Error: /sys/class/backlight is empty.");
         return;
     }
     int max_value = read_max_backlight(driver);
@@ -118,7 +115,6 @@ static void decreases_blacklight()
 {
     char *driver = get_driver();
     if( driver == NULL ) {
-        fprintf(stderr, "Error: /sys/class/backlight is empty.");
         return;
     }
     int max_value = read_max_backlight(driver);
@@ -140,6 +136,9 @@ static void set_backlight_from_stdin()
     char *driver = get_driver();
     int ok = True, value;
     int max_value = read_max_backlight(driver);
+    if( driver == NULL ) {
+        return;
+    }
     while(ok && !feof(stdin)) {
         ok = scanf("%d", &value);
         if( ok != EOF && value > 0 && value <= max_value) {

From 3b1610dd32e015b2625008235be44f51cae4a8c8 Mon Sep 17 00:00:00 2001
From: Matthias Gerstner <matthias.gerstner@suse.de>
Date: Wed, 13 Jun 2018 17:23:49 +0200
Subject: [PATCH 6/8] lxqtbacklight: removed extra whitespace

---
 lxqtbacklight/linux_backend/driver/libbacklight_backend.c  | 6 +++---
 lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
index 484e3d5..733fe9e 100644
--- a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
@@ -171,12 +171,12 @@ char *lxqt_backlight_backend_get_driver()
 {
     DIR *dirp;
     struct dirent *dp;
-    
+
     char *drivers[N_BACKLIGHT];
     char *driver;
     int n;
     char type[1024];
-    
+
     for(n=0;n<N_BACKLIGHT;n++)
         drivers[n] = NULL;
 
@@ -217,7 +217,7 @@ char *lxqt_backlight_backend_get_driver()
     if (errno != 0) {
         fprintf(stderr, "Error reading directory %s: %s\n", sysfs_backlight_dir, strerror(errno));
     }
-    
+
     driver = NULL;
     for(n=0;n<N_BACKLIGHT;n++) {
         if( drivers[n] != NULL && driver == NULL )
diff --git a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
index bcf2b9e..3e545a8 100644
--- a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
@@ -182,7 +182,7 @@ int main(int argc, char *argv[])
             return 0;
         } if( !strcmp(argv[n], "--dec") ) {
             decreases_blacklight();
-            return 0; 
+            return 0;
         } if( !strcmp(argv[n], "--stdin") ) {
             set_backlight_from_stdin();
             return 0;
@@ -195,12 +195,12 @@ int main(int argc, char *argv[])
             return 0;
         }
     }
-    
+
     if( argc == 1 ) {
         help(argv[0]);
         return 0;
     }
-    
+
     change_blacklight(value, value_percent_ok);
 
     return 0;

From f5c4cc47f60c674df2cc8a93343526a69c54a1aa Mon Sep 17 00:00:00 2001
From: Matthias Gerstner <matthias.gerstner@suse.de>
Date: Wed, 13 Jun 2018 18:01:36 +0200
Subject: [PATCH 7/8] lxqtbacklight: fix and improve command line parameter
 handling

- the percent variant didn't work before, because the logic was wrong
- detect non-numerical unsupported arguments and print usage in this case
- support 0% and 100% but avoid turning off the backlight completely
---
 .../linux_backend/driver/lxqtbacklight_backend.c         | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
index 3e545a8..836e3f3 100644
--- a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
@@ -22,6 +22,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+#include <ctype.h>
 
 #include "libbacklight_backend.h"
 #include "libbacklight_backend.c"
@@ -83,9 +84,14 @@ static void change_blacklight(int value, int percent_ok)
         return;
     }
     int max_value = read_max_backlight(driver);
-    if(percent_ok)
+    if(percent_ok) {
         value = (float)(max_value*value)/100.0;
-    if(value<max_value && value>0) {
+        if( value == 0 ) {
+            // avoid switching off backlight but support zero as lowest value
+            value = 1;
+        }
+    }
+    if(value<=max_value && value>0) {
         set_backlight(driver, value);
     }
     free(driver);
@@ -186,10 +192,10 @@ int main(int argc, char *argv[])
         } if( !strcmp(argv[n], "--stdin") ) {
             set_backlight_from_stdin();
             return 0;
-        } else if ( argv[n][0] != '-' ) {
-            value = atoi(argv[1]);
-        } else if ( argv[n][0] != '%' && strlen(argv[n])==1 ) {
+        } else if ( !strcmp(argv[n], "%") ) {
             value_percent_ok = True;
+        } else if ( isdigit(argv[n][0]) ) {
+            value = atoi(argv[n]);
         } else {
             help(argv[0]);
             return 0;

From 7bd68881d6a65541437f2e4dfad0f6749b12034b Mon Sep 17 00:00:00 2001
From: Matthias Gerstner <matthias.gerstner@suse.de>
Date: Thu, 14 Jun 2018 11:28:14 +0200
Subject: [PATCH 8/8] lxqtbacklight: only pass basename into open_driver_file()

this way the sysfs directory path is centrally defined and the code
becomes better readable.
---
 .../linux_backend/driver/libbacklight_backend.c        | 18 +++++++++---------
 .../linux_backend/driver/lxqtbacklight_backend.c       |  4 ++--
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
index 733fe9e..1282706 100644
--- a/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/libbacklight_backend.c
@@ -68,7 +68,7 @@
 #define True 1
 #define False 0
 
-static FILE* open_driver_file(const char *path, const char *driver, const char *mode);
+static FILE* open_driver_file(const char *file, const char *driver, const char *mode);
 static int read_backlight(const char *driver);
 static int read_max_backlight(const char *driver);
 static int read_bl_power(const char *driver);
@@ -114,9 +114,9 @@ int lxqt_backlight_is_backlight_off()
     return bl_power;
 }
 
-static int read_int(const char *tpl, const char *driver)
+static int read_int(const char *file, const char *driver)
 {
-    FILE *in = open_driver_file(tpl, driver, "r");
+    FILE *in = open_driver_file(file, driver, "r");
     if( in == NULL ) {
         return -1;
     }
@@ -129,12 +129,12 @@ static int read_int(const char *tpl, const char *driver)
     return value;
 }
 
-static FILE* open_driver_file(const char *tpl, const char *driver, const char *mode)
+static FILE* open_driver_file(const char *file, const char *driver, const char *mode)
 {
     char path[PATH_MAX];
     int res;
 
-    res = snprintf(path, PATH_MAX, tpl, driver);
+    res = snprintf(path, PATH_MAX, "%s/%s/%s", sysfs_backlight_dir, driver, file);
 
     if( res <= 0 || res >= PATH_MAX ) {
         path[0] = '\0';
@@ -152,17 +152,17 @@ static FILE* open_driver_file(const char *tpl, const char *driver, const char *m
 
 static int read_backlight(const char *driver)
 {
-    return read_int("/sys/class/backlight/%s/actual_brightness", driver);
+    return read_int("actual_brightness", driver);
 }
 
 static int read_max_backlight(const char *driver)
 {
-    return read_int("/sys/class/backlight/%s/max_brightness", driver);
+    return read_int("max_brightness", driver);
 }
 
 static int read_bl_power(const char *driver)
 {
-    return read_int("/sys/class/backlight/%s/bl_power", driver);
+    return read_int("bl_power", driver);
 }
 
 typedef enum {FIRMWARE, PLATFORM, RAW, OTHER, N_BACKLIGHT} BackligthTypes;
@@ -191,7 +191,7 @@ char *lxqt_backlight_backend_get_driver()
             if( !strcmp(dp->d_name, ".") || !strcmp(dp->d_name, "..") )
                 continue;
             driver = dp->d_name;
-            FILE *in = open_driver_file("/sys/class/backlight/%s/type", driver, "r");
+            FILE *in = open_driver_file("type", driver, "r");
             if( in == NULL )
                 continue;
             // the maximum field width does not include '\0'!
diff --git a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
index 836e3f3..8886a74 100644
--- a/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
+++ b/lxqtbacklight/linux_backend/driver/lxqtbacklight_backend.c
@@ -36,7 +36,7 @@
  */
 static void set_bl_power(const char *driver, int value)
 {
-    FILE *out = open_driver_file("/sys/class/backlight/%s/bl_power", driver, "w");
+    FILE *out = open_driver_file("bl_power", driver, "w");
     if( out != NULL ) {
         fprintf(out, "%d", value);
         fclose(out);
@@ -47,7 +47,7 @@ static void set_bl_power(const char *driver, int value)
 static void set_backlight(const char *driver, int value)
 {
     if(value>0) {
-        FILE *out = open_driver_file("/sys/class/backlight/%s/brightness", driver, "w");
+        FILE *out = open_driver_file("brightness", driver, "w");
         if( out != NULL ) {
             fprintf(out, "%d", value);
             fclose(out);