mdev: use $DEVNAME in uevent sysfs file for device node name

516530c932bd17d87c9eb4347a490be051e495f4 uses $DEVNAME variable
for device node name. This is fine, but only works for hotplugging,
"mdev -s" will behave differently when DEVNAME and basename(path)
differ.

This patch extracts the DEVNAME from the uevent sysfs file in
make_device(), thus works for hot- and coldplugging; so using
the environment DEVNAME on hotplug events is no longer necessary.

Signed-off-by: Nikolaus Voss <n.voss@weinmann.de>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 35 insertions, 12 deletions

diff --git a/util-linux/mdev.c b/util-linux/mdev.c
index 1d741367e..e80b58f2e 100644
--- a/util-linux/mdev.c
+++ b/util-linux/mdev.c
@@ -295,8 +295,8 @@ struct globals {
 /* Prevent infinite loops in /sys symlinks */
 #define MAX_SYSFS_DEPTH 3
 
-/* We use additional 64+ bytes in make_device() */
-#define SCRATCH_SIZE 80
+/* We use additional bytes in make_device() */
+#define SCRATCH_SIZE 128
 
 #if ENABLE_FEATURE_MDEV_CONF
 
@@ -541,7 +541,7 @@ static char *build_alias(char *alias, const char *device_name)
 
 /* mknod in /dev based on a path like "/sys/block/hda/hda1"
  * NB1: path parameter needs to have SCRATCH_SIZE scratch bytes
- * after NUL, but we promise to not mangle (IOW: to restore if needed)
+ * after NUL, but we promise to not mangle (IOW: to restore NUL if needed)
  * path string.
  * NB2: "mdev -s" may call us many times, do not leak memory/fds!
  *
@@ -551,6 +551,7 @@ static char *build_alias(char *alias, const char *device_name)
 static void make_device(char *device_name, char *path, int operation)
 {
         int major, minor, type, len;
+        char *path_end = path + strlen(path);
 
         /* Try to read major/minor string.  Note that the kernel puts \n after
          * the data, so we don't need to worry about null terminating the string
@@ -559,17 +560,15 @@ static void make_device(char *device_name, char *path, int operation)
          */
         major = -1;
         if (operation == OP_add) {
-                char *dev_maj_min = path + strlen(path);
-
-                strcpy(dev_maj_min, "/dev");
-                len = open_read_close(path, dev_maj_min + 1, 64);
-                *dev_maj_min = '\0';
+                strcpy(path_end, "/dev");
+                len = open_read_close(path, path_end + 1, SCRATCH_SIZE - 1);
+                *path_end = '\0';
                 if (len < 1) {
                         if (!ENABLE_FEATURE_MDEV_EXEC)
                                 return;
                         /* no "dev" file, but we can still run scripts
                          * based on device name */
-                } else if (sscanf(++dev_maj_min, "%u:%u", &major, &minor) == 2) {
+                } else if (sscanf(path_end + 1, "%u:%u", &major, &minor) == 2) {
                         dbg1("dev %u,%u", major, minor);
                 } else {
                         major = -1;
@@ -577,9 +576,33 @@ static void make_device(char *device_name, char *path, int operation)
         }
         /* else: for delete, -1 still deletes the node, but < -1 suppresses that */
 
-        /* Determine device name, type, major and minor */
-        if (!device_name)
-                device_name = (char*) bb_basename(path);
+        /* Determine device name */
+        if (!device_name) {
+                /*
+                 * There was no $DEVNAME envvar (for example, mdev -s never has).
+                 * But it is very useful: it contains the *path*, not only basename,
+                 * Thankfully, uevent file has it.
+                 * Example of .../sound/card0/controlC0/uevent file on Linux-3.7.7:
+                 * MAJOR=116
+                 * MINOR=7
+                 * DEVNAME=snd/controlC0
+                 */
+                strcpy(path_end, "/uevent");
+                len = open_read_close(path, path_end + 1, SCRATCH_SIZE - 1);
+                if (len < 0)
+                        len = 0;
+                *path_end = '\0';
+                path_end[1 + len] = '\0';
+                device_name = strstr(path_end + 1, "\nDEVNAME=");
+                if (device_name) {
+                        device_name += sizeof("\nDEVNAME=")-1;
+                        strchrnul(device_name, '\n')[0] = '\0';
+                } else {
+                        /* Fall back to just basename */
+                        device_name = (char*) bb_basename(path);
+                }
+        }
+        /* Determine device type */
         /*
          * http://kernel.org/doc/pending/hotplug.txt says that only
          * "/sys/block/..." is for block devices. "/sys/bus" etc is not.