From: Kay Sievers <kay@vrfy.org>
Date: Fri, 3 Aug 2012 08:52:24 +0000 (+0200)
Subject: udev: path_id - add comment about the unrteliable rebase logic
X-Git-Tag: v188~38
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=commitdiff_plain;h=1c7dfbf249f5320d0675fcb03556a55881e21457;hp=3bea51c59d79333a2a365f4677c97b4302377a48;ds=inline

udev: path_id - add comment about the unrteliable rebase logic
---

diff --git a/src/udev/udev-builtin-path_id.c b/src/udev/udev-builtin-path_id.c
index 8eac991d3..720f616da 100644
--- a/src/udev/udev-builtin-path_id.c
+++ b/src/udev/udev-builtin-path_id.c
@@ -236,7 +236,23 @@ static struct udev_device *handle_scsi_default(struct udev_device *parent, char
         if (sscanf(name, "%d:%d:%d:%d", &host, &bus, &target, &lun) != 4)
                 return NULL;
 
-        /* rebase host offset to get the local relative number */
+        /*
+         * Rebase host offset to get the local relative number
+         *
+         * Note: This is by definition racy, unreliable and too simple.
+         * Please do not copy this model anywhere. It's just a left-over
+         * from the time we had no idea how things should look like in
+         * the end.
+         *
+         * Making assumptions about a global in-kernel counter and use
+         * that to calculate a local offset is a very broken concept. It
+         * can only work as long as things are in strict order.
+         *
+         * The kernel needs to export the instance/port number of a
+         * controller directly, without the need for rebase magic like
+         * this. Manual driver unbind/bind, parallel hotplug/unplug will
+         * get into the way of this "I hope it works" logic.
+         */
         basenum = -1;
         base = strdup(udev_device_get_syspath(hostdev));
         if (base == NULL)