Feature changed by: Tejun Heo (teheo) Feature #305584, revision 12 Title: Do not assume fixed and contiguous device numbers in installation and management tools for storage openSUSE-11.2: Evaluation Priority Requester: Mandatory Projectmanager: Important Requested by: Matthias Eckermann (mge1512) Requested by: Tejun Heo (teheo) Description: Subject: [Research] head up on upcoming extended block devt change From: Tejun Heo Date: Thu, 18 Dec 2008 12:59:21 +0900 Reply-To: research@suse.de Hello, all. From soon to be released 2.6.28, the kernel contains extended block devt support, which basically allocates block device numbers dynamically from major number 259 (might expand to other major numbers if ever necessary). This means that device numbers belonging to the same device become non-contiguous and can be on different major numbers. This will remove the 15 partition limit on /dev/sdX's and increase the total number of supported SCSI disks considerably. Also, it's used by md to allow partitioning of /dev/mdX's thus removing the distinction of partitionable and non-partitionable md devices. For example, /dev/sda with 60 partitions can look like as follows. # cat /proc/partitions major minor #blocks name 8 0 156290904 sda 8 1 8001 sda1 8 2 8032 sda2 8 3 8032 sda3 8 4 1 sda4 ... 8 15 8001 sda15 259 0 8001 sda16 259 1 8001 sda17 259 2 8001 sda18 ... 259 43 8001 sda59 259 44 8001 sda60 For detailed overview, please take a look at the following message. http://article.gmane.org/gmane.linux.kernel/701825 As device node creation is completely dynamic these days, installed systems usually can cope fine with this change; however, in installation and management tools, there seem to be many places which assume fixed and contiguous device numbers. To ease hunting down those areas, a debug option is available which forces every block device to be allocated on the dynamic major non-consecutively. With the debug option turned on, the above disk will look like the following. # cat /proc/partitions major minor #blocks name 8 0 156290904 sda 259 262144 8001 sda1 259 786432 8032 sda2 259 131072 8032 sda3 259 655360 1 sda4 259 393216 8001 sda5 259 917504 8001 sda6 259 65536 8001 sda7 ... 259 114688 8001 sda55 259 638976 8001 sda56 259 376832 8001 sda57 259 901120 8001 sda58 259 245760 8001 sda59 259 770048 8001 sda60 So, the installation / management tools need to follow /sys/block/*/device/driver to determine which type of device it is and use /sys/block/*/dev to determine its device number. I'll add a kernel parameter (say, block.force_ext_devt) so that this debug option can be turned on and off during boot so that people who don't work on related subsystems don't have to suffer. I'm not sure how and when to proceed with this yet but I definitely think we'll need plenty of time to sort this out completely. Any ideas on how to proceed on this? Thanks. -- tejun Discussion: #1: Tejun Heo (teheo) (2008-12-22 13:31:11) So... when and how do we proceed with things like this? I wanna enable it in HEAD but SLES11 hasn't branched out from HEAD yet but I don't think we should wait till SLES11 is released. #2: Matthias Eckermann (mge1512) (2008-12-22 10:24:58) (reply to #1) SLE 11 has precedence over anything else we currently do - with respect to focus and time spent on it. Thus we should concentrate on SLE 11 and wait with those changes after release of SLE 11. There are more than enough P1 and P2 issues with the SLE 11 kernel to work on, ... Vojtech? #3: Vojtech Pavlik (vojtech_pavlik) (2008-12-22 12:14:19) I agree, Matthias, and I see no reason why this couldn't wait until SLES11 branches out of HEAD. #4: Tejun Heo (teheo) (2008-12-23 11:52:19) Alright, then. I'll enable it when SLES11 branches out. Thanks. + #5: Tejun Heo (teheo) (2009-05-29 16:55:23) + Added genhd.mangle_devt parameter and enabled DEBUG_BLOCK_EXT_DEVT for + all configs except for vanilla's and ppc/ps3. Ext major and mangled + minor can be enabled by specifying "genhd.mangle_devt=1" as kernel + parameter. Have fun. :-) -- openSUSE Feature: https://features.opensuse.org/305584