From 937309d3e305c699fb1264f2561bf3ee4daa697d Mon Sep 17 00:00:00 2001
From: Jeremy Compostella <jeremy.compostella@intel.com>
Date: Fri, 3 Mar 2017 16:27:29 +0100
Subject: [PATCH] ueventd: support by-name symlinks for virtual block devices

This patch makes ueventd create by-name symlinks for virtual block
devices when Android is running as a Xen guest OS.

The symlinks will be created under /dev/block/vbd/. For example:
/dev/block/vbd/768/by-name/

Change-Id: Id45da560d13f641d7c8419511c154de9ae8a4ec9
Test: manual
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
---
 init/devices.cpp | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/init/devices.cpp b/init/devices.cpp
index bd11f5fa4..405f92e17 100644
--- a/init/devices.cpp
+++ b/init/devices.cpp
@@ -390,6 +390,34 @@ static int find_pci_device_prefix(const char *path, char *buf, ssize_t buf_sz)
     return 0;
 }
 
+/* Given a path that may start with a virtual block device, populate
+ * the supplied buffer with the virtual block device ID and return 0.
+ * If it doesn't start with a virtual block device, or there is some
+ * error, return -1 */
+static int find_vbd_device_prefix(const char *path, char *buf, ssize_t buf_sz)
+{
+    const char *start, *end;
+
+    /* Beginning of the prefix is the initial "vbd-" after "/devices/" */
+    if (strncmp(path, "/devices/vbd-", 13))
+        return -1;
+
+    /* End of the prefix is one path '/' later, capturing the
+       virtual block device ID. Example: 768 */
+    start = path + 13;
+    end = strchr(start, '/');
+    if (!end)
+        return -1;
+
+    /* Make sure we have enough room for the string plus null terminator */
+    if (end - start + 1 > buf_sz)
+        return -1;
+
+    strncpy(buf, start, end - start);
+    buf[end - start] = '\0';
+    return 0;
+}
+
 static void parse_event(const char *msg, struct uevent *uevent)
 {
     uevent->action = "";
@@ -516,6 +544,9 @@ static char **get_block_device_symlinks(struct uevent *uevent)
     } else if (!find_pci_device_prefix(uevent->path, buf, sizeof(buf))) {
         device = buf;
         type = "pci";
+    } else if (!find_vbd_device_prefix(uevent->path, buf, sizeof(buf))) {
+        device = buf;
+        type = "vbd";
     } else {
         return NULL;
     }