From: Lennart Poettering <lennart@poettering.net>
Date: Thu, 31 Mar 2022 08:10:37 +0000 (+0200)
Subject: udev: add /dev/disk/by-diskseq symlink for block devices
X-Git-Tag: v251-rc2~224
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=0d08db7f89ee665a9dcb6dd66c1f9e203192e8ec;p=thirdparty%2Fsystemd.git

udev: add /dev/disk/by-diskseq symlink for block devices

This adds another symlink for block devices:

    /dev/disk/by-diskseq/<number>

where the number is the diskseq number as exposed by the kernel. It's
useful for apps because they can use it to open a device by diskseq, in
a way that is safe against device node reuse. I.e. if a device node path
like this is passed to an app it could open the device node via the
symlink and also parse the diskseq from the path. Once the device is
opened it could compare the parsed diskseq with the one returned by
BLKGETDISKSEQ on the open node, and if it matches they know they are
talking to the right device.

Fixes: #22906
---

diff --git a/rules.d/60-persistent-storage.rules b/rules.d/60-persistent-storage.rules
index 6ac17f2b645..23f43e4f976 100644
--- a/rules.d/60-persistent-storage.rules
+++ b/rules.d/60-persistent-storage.rules
@@ -121,4 +121,9 @@ ENV{DEVTYPE}=="partition", ENV{ID_WWN_WITH_EXTENSION}=="?*", SYMLINK+="disk/by-i
 ENV{ID_PART_ENTRY_UUID}=="?*", SYMLINK+="disk/by-partuuid/$env{ID_PART_ENTRY_UUID}"
 ENV{ID_PART_ENTRY_SCHEME}=="gpt", ENV{ID_PART_ENTRY_NAME}=="?*", SYMLINK+="disk/by-partlabel/$env{ID_PART_ENTRY_NAME}"
 
+# by-diskseq link (if an app is told to open a path like this, they may parse
+# the diskseq number from the path, then issue BLKGETDISKSEQ to verify they really got
+# the right device, to access specific disks in a race-free fashion)
+ENV{DISKSEQ}=="?*", ENV{DEVTYPE}!="partition", SYMLINK+="disk/by-diskseq/$env{DISKSEQ}"
+
 LABEL="persistent_storage_end"