init: Add symlinks to USB character devices

Since we now support USB host mode, devices might get a different device
file depending if other devices are connected on the host port. This
patch creates symlinks to USB character devices that depend on the port
devices are connected to, but not on the order they have been probed.
(e.g. /dev/usb/tty2-1:1.0 -> /dev/ttyUSB0)

Change-Id: I285bcc2d59446fbff8a7abbe39c21781f3bb4bd3

1 files changed, 52 insertions, 0 deletions

diff --git a/init/devices.c b/init/devices.c
index 8e912de..21e1ee3 100644
--- a/init/devices.c
+++ b/init/devices.c
@@ -264,6 +264,57 @@ static void parse_event(const char *msg, struct uevent *uevent)
                     uevent->firmware, uevent->major, uevent->minor);
 }
 
+static char **get_character_device_symlinks(struct uevent *uevent)
+{
+    const char *parent;
+    char *slash;
+    char **links;
+    int link_num = 0;
+    int width;
+
+    if (strncmp(uevent->path, "/devices/platform/", 18))
+        return NULL;
+
+    links = malloc(sizeof(char *) * 2);
+    if (!links)
+        return NULL;
+    memset(links, 0, sizeof(char *) * 2);
+
+    /* skip "/devices/platform/<driver>" */
+    parent = strchr(uevent->path + 18, '/');
+    if (!*parent)
+        goto err;
+
+    if (!strncmp(parent, "/usb", 4)) {
+        /* skip root hub name and device. use device interface */
+        while (*++parent && *parent != '/');
+        if (*parent)
+            while (*++parent && *parent != '/');
+        if (!*parent)
+            goto err;
+        slash = strchr(++parent, '/');
+        if (!slash)
+            goto err;
+        width = slash - parent;
+        if (width <= 0)
+            goto err;
+
+        if (asprintf(&links[link_num], "/dev/usb/%s%.*s", uevent->subsystem, width, parent) > 0)
+            link_num++;
+        else
+            links[link_num] = NULL;
+        mkdir("/dev/usb", 0755);
+    }
+    else {
+        goto err;
+    }
+
+    return links;
+err:
+    free(links);
+    return NULL;
+}
+
 static char **parse_platform_block_device(struct uevent *uevent)
 {
     const char *driver;
@@ -407,6 +458,7 @@ static void handle_device_event(struct uevent *uevent)
             name += 4;
         } else
             base = "/dev/";
+        links = get_character_device_symlinks(uevent);
     }
 
     if (!devpath_ready)