Red Hat Bugzilla – Bug 731785
RFE: add option to dmsetup to display device names for "dmsetup deps"
Last modified: 2012-06-20 10:52:01 EDT
dmsetup deps should allow display of sd device name instead of (major,minor) pairs. Example: dmsetup deps mpathf 2 dependencies : (8, 112) (65, 16) desired output 2 dependencies : (sdh) (sdr) It's understandable that the major,minor pairs are displayed, since dmsetup is dumping kernel information, and device names are only known in userspace. However, this should be achievable by adding the following to dmsetup: 1) an sane command option to dmsetup to display device names 2) a method for mapping a major/minor pair to userspace visible device name, such as sysfs lookup or /proc/partitions Details of the request dmsetup uses device names instead of (maj,min) numbers What is the nature and description of the request? Using major minor numbers for everything can be very confusing. It requires you to cross reference everything by doing a ls -l /dev every time you want to relate dmsetup to another utility, for example, iostat. Why does the customer need this? (List the business requirements here) To save time and make the lives of the systems/storage administrators easier. How would the customer like to achieve this? (List the functional requirements here) Have dmsetup look the name up, and then put that out instead of maj,min. May require a new flag for compatbility For each functional requirement listed in question 4, specify how Red Hat and the customer can test to confirm the requirement is successfully implemented. 1) dmsetup deps mpathf 2) output shows device name and not (maj,min) Is there already an existing RFE upstream or in Red Hat bugzilla? Not that I could find: https://bugzilla.redhat.com/buglist.cgi?query_format=advanced&bug_status=NEW&bug_status=ASSIGNED&component=device-mapper-multipath&product=Red%20Hat%20Enterprise%20Linux%206&classification=Red%20Hat How quickly does this need resolved? (desired target release) minor Does this request meet the RHEL Bug and Feature Inclusion Criteria (please review) yes List the affected packages device-mapper device-mapper-multipath Would the customer be able to assist in testing this functionality if implemented? yes
It would be nice, but please note I had RFE for lsblk which provide exactly these simple listings based on sysfs (over all storage devices, not only DM): # lsblk /dev/sda NAME MAJ:MIN RM SIZE RO MOUNTPOINT sda 8:0 0 68.4G 0 ├─sda1 8:1 0 196.1M 0 /boot ├─sda2 8:2 0 996.2M 0 [SWAP] ├─sda3 8:3 0 33.6G 0 └─sda4 8:4 0 33.6G 0 └─vg_rhel6-root (dm-0) 253:0 0 33.6G 0 / Do they know about it? (it is in released version already.)
For scripts it's also often easier to follow the deps directly in sysfs via the symlinks in the /sys/block/<device>/slaves directory.
(In reply to comment #1) > It would be nice, but please note I had RFE for lsblk which provide exactly > these simple listings based on sysfs (over all storage devices, not only DM): > > # lsblk /dev/sda > NAME MAJ:MIN RM SIZE RO MOUNTPOINT > sda 8:0 0 68.4G 0 > ├─sda1 8:1 0 196.1M 0 /boot > ├─sda2 8:2 0 996.2M 0 [SWAP] > ├─sda3 8:3 0 33.6G 0 > └─sda4 8:4 0 33.6G 0 > └─vg_rhel6-root (dm-0) 253:0 0 33.6G 0 / > > Do they know about it? (it is in released version already.) You could either do a ls -l or use lsblk, but this still requires two steps. dmsetup, then lsblk. It would be more convenient if it was just dmsetup and that made sense of everything. Also, all of these solutions are a devname -> maj,min mapping, as far as I know there isn't a way to get maj:min -> devname mapping.
Perhaphs not exactly what you want, but: for DM: cat /sys/dev/block/$MAJOR:$MINOR/dm/name dmsetup deps -j $MAJOR -m $MINOR (hm, and lsblk has no such option, seems like a bug:-) or maybe lsblk /dev/block/$MAJOR:$MINOR
Patches posted to lvm-devel for review: https://www.redhat.com/archives/lvm-devel/2011-November/msg00026.html https://www.redhat.com/archives/lvm-devel/2011-November/msg00027.html
After a review and further discussion, the final output is as follows (an example with one linear [lvol0] and one mirror [lvol1] LVM2 volume): ------------------ dmsetup info -c -o ------------------ [0] rawhide/~ # dmsetup info -c -o name,blkdevname,devnos_used,blkdevs_used Name BlkDevName DevNos BlkDevNames vg-lvol1 dm-4 253:3,253:2,253:1 dm-3,dm-2,dm-1 vg-lvol1_mimage_1 dm-3 8:80 sdf vg-lvol0 dm-0 8:64 sde vg-lvol1_mimage_0 dm-2 8:64 sde vg-lvol1_mlog dm-1 8:128 sdi ------------ dmsetup deps ------------ [0] rawhide/~ # dmsetup deps vg-lvol1: 3 dependencies : (253, 3) (253, 2) (253, 1) vg-lvol1_mimage_1: 1 dependencies : (8, 80) vg-lvol0: 1 dependencies : (8, 64) vg-lvol1_mimage_0: 1 dependencies : (8, 64) vg-lvol1_mlog: 1 dependencies : (8, 128) [0] rawhide/~ # dmsetup deps -o devno vg-lvol1: 3 dependencies : (253, 3) (253, 2) (253, 1) vg-lvol1_mimage_1: 1 dependencies : (8, 80) vg-lvol0: 1 dependencies : (8, 64) vg-lvol1_mimage_0: 1 dependencies : (8, 64) vg-lvol1_mlog: 1 dependencies : (8, 128) [0] rawhide/~ # dmsetup deps -o blkdevname vg-lvol1: 3 dependencies : (dm-3) (dm-2) (dm-1) vg-lvol1_mimage_1: 1 dependencies : (sdf) vg-lvol0: 1 dependencies : (sde) vg-lvol1_mimage_0: 1 dependencies : (sde) vg-lvol1_mlog: 1 dependencies : (sdi) [0] rawhide/~ # dmsetup deps -o devname vg-lvol1: 3 dependencies : (vg-lvol1_mimage_1) (vg-lvol1_mimage_0) (vg-lvol1_mlog) vg-lvol1_mimage_1: 1 dependencies : (sdf) vg-lvol0: 1 dependencies : (sde) vg-lvol1_mimage_0: 1 dependencies : (sde) vg-lvol1_mlog: 1 dependencies : (sdi) [0] rawhide/~ # dmsetup deps -o abc Option not recognised: abc Couldn't process command line. ---------- dmsetup ls ---------- [0] rawhide/~ # dmsetup ls vg-lvol1 (253:4) vg-lvol1_mimage_1 (253:3) vg-lvol0 (253:0) vg-lvol1_mimage_0 (253:2) vg-lvol1_mlog (253:1) [0] rawhide/~ # dmsetup ls -o devno vg-lvol1 (253:4) vg-lvol1_mimage_1 (253:3) vg-lvol0 (253:0) vg-lvol1_mimage_0 (253:2) vg-lvol1_mlog (253:1) [0] rawhide/~ # dmsetup ls -o devname vg-lvol1 (vg-lvol1) vg-lvol1_mimage_1 (vg-lvol1_mimage_1) vg-lvol0 (vg-lvol0) vg-lvol1_mimage_0 (vg-lvol1_mimage_0) vg-lvol1_mlog (vg-lvol1_mlog) [0] rawhide/~ # dmsetup ls -o blkdevname vg-lvol1 (dm-4) vg-lvol1_mimage_1 (dm-3) vg-lvol0 (dm-0) vg-lvol1_mimage_0 (dm-2) vg-lvol1_mlog (dm-1) [0] rawhide/~ # dmsetup ls -o abc Option not recognised: abc Couldn't process command line. ----------------- dmsetup ls --tree ----------------- [0] rawhide/~ # dmsetup ls --tree vg-lvol1 (253:4) |-vg-lvol1_mimage_1 (253:3) | `- (8:80) |-vg-lvol1_mimage_0 (253:2) | `- (8:64) `-vg-lvol1_mlog (253:1) `- (8:128) vg-lvol0 (253:0) `- (8:64) [0] rawhide/~ # dmsetup ls --tree -o blkdevname vg-lvol1 <dm-4> (253:4) |-vg-lvol1_mimage_1 <dm-3> (253:3) | `- <sdf> (8:80) |-vg-lvol1_mimage_0 <dm-2> (253:2) | `- <sde> (8:64) `-vg-lvol1_mlog <dm-1> (253:1) `- <sdi> (8:128) vg-lvol0 <dm-0> (253:0) `- <sde> (8:64) [0] rawhide/~ # dmsetup ls --tree -o abc Tree options not recognised: abc Couldn't process command line. -------------------------------------------------------------- Briefly: * devno == major and minor pair blkdevname == kernel (block device) name (e.g. dm-0, sda, md0, ...) devname == map name for dm devices (the one found in /dev/mapper dir), equal to blkdevname for non-dm devices * new '-o' switch with possible options of '{devno|blkdevname|devname}' for dmsetup deps and ls * new '-o blkdevname' option for dmsetup ls --tree (ls --tree already had the '-o' switch so this is just an addition of a new option for completeness and consistency with other commmands) * new '-c -o blkdevname,blkdevs_used' options for dmsetup info -c -o Notice: 'devname' works only with kernels >= 2.6.29 (it reads /sys/dev/block/major:minor/dm/name content). For olders kernels, the 'devname' is equal to 'blkdevname'.
upstream lvm2 v2.02.89/libdevmapper 1.02.68
I've renamed the headers to make it more comprehensible: DevNames --> DevNamesUsed BlkDevNames --> BlkDevNamesUsed DevNos --> DevNosUsed So we have: [0] devel/~ # dmsetup info -c -o name,blkdevname,devs_used,devnos_used,blkdevs_used Name BlkDevName DevNamesUsed DevNosUsed BlkDevNamesUsed c dm-2 b,a 253:1,253:0 dm-1,dm-0 b dm-1 8:16 sdb a dm-0 8:0 sda It's just a header rename, so it should not cause any harm (scripts use --noheadings anyway).
Technical note added. If any revisions are required, please edit the "Technical Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: The dmsetup command now supports displaying block device names for any devices listed on deps, ls and info command output. For dmsetup 'deps' and 'ls' command, it's possible to switch among 'devno' (major and minor number, the default and the original behaviour), 'devname' (mapping name for a device-mapper device, block device name otherwise) and 'blkdevname' (always display a block device name). For dmsetup 'info' command, it's possible to use new 'blkdevname' and 'blkdevs_used' fields.
(In reply to comment #12) > I've renamed the headers to make it more comprehensible: > > DevNames --> DevNamesUsed > BlkDevNames --> BlkDevNamesUsed > DevNos --> DevNosUsed Renamed in lvm2-2.02.95-6.el6.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. http://rhn.redhat.com/errata/RHBA-2012-0962.html