Red Hat Bugzilla – Bug 719760
pvcreate with "linear" md device causes "sysfs attr level not in expected format: linear"
Last modified: 2013-02-28 23:10:21 EST
Description of problem: [root@PG803 ~]# mdadm --create /dev/md0 -c 32 -l linear -f -n1 /dev/sddlmaa1 mdadm: array /dev/md0 started. [root@PG803 ~]# pvcreate /dev/md0 /dev/md0 sysfs attr level not in expected format: linear Physical volume "/dev/md0" successfully created Version-Release number of selected component (if applicable): all Additional info: This is an easy fix. Net-net: 1. For this customer, we need to figure out if the md chunksize is relevant for a linear md. If not, the message can be safely ignored. 2. We could submit a patch to lvm code to fix the error. Analysis static int _md_sysfs_attribute_scanf(const char *sysfs_dir, struct device *dev, const char *attribute_name, const char *attribute_fmt, void *attribute_value) { ... int ret = 0; ... if ((ret = sscanf(buffer, attribute_fmt, attribute_value)) != 1) { log_error("%s sysfs attr %s not in expected format: %s", dev_name(dev), attribute_name, buffer); goto out; } out: return ret; } /* * Retrieve level from md device using sysfs. */ static int dev_md_level(const char *sysfs_dir, struct device *dev) { const char *attribute = "level"; int level = -1; if (_md_sysfs_attribute_scanf(sysfs_dir, dev, attribute, "raid%d", &level) != 1) return -1; ... } /* * Calculate stripe width of md device using its sysfs files. */ unsigned long dev_md_stripe_width(const char *sysfs_dir, struct device *dev) { ... level = dev_md_level(sysfs_dir, dev); if (level < 0) return 0; ... } The only caller of dev_md_stripe_width() is: unsigned long set_pe_align(struct physical_volume *pv, unsigned long data_alignment) { if (pv->pe_align) goto out; if (data_alignment) pv->pe_align = data_alignment; else pv->pe_align = MAX(65536UL, lvm_getpagesize()) >> SECTOR_SHIFT; if (!pv->dev) goto out; /* * Align to stripe-width of underlying md device if present */ if (find_config_tree_bool(pv->fmt->cmd, "devices/md_chunk_alignment", DEFAULT_MD_CHUNK_ALIGNMENT)) pv->pe_align = MAX(pv->pe_align, dev_md_stripe_width(pv->fmt->cmd->sysfs_dir, pv->dev)); ... } So we're setting the pv->pe_align value based on the MAX value of any calculated md_stripe width. But when we get the above error, we'll get the following call chain: -->dev_md_stripe_width() returns 0 -->dev_md_level() returns -1 -->_md_sysfs_attribute_scanf() returns != 1, sscanf fail, ("linear" does not match "raid%d") So our equation becomes: MAX(pv->pe_align, 0) == pv->pe_align No adjustment is made for the md stripe width if it is "linear".
Well, I would really like to know why you want to using LVM over linear MD - some very special case? Anyway, detection shuould work here (linear has proper chunk_size 0 in sysfs), so fix should be trivial.
Reading the code, I do not think there is a bug. linear (and the same will be MD multipath) has chunk_size 0, code properly use that. So what's the problem? MD linear is just JBOD, there is nothing like chuck size, why do you want to apply some value here?
The bug is just the error message, which caused a customer call, and the fact it was not obvious without code inspection whether this was something to be concerned about. Maybe it should be log_warn in this case, or not print anything?
# mdadm -C --rounding=32 -l linear -n 2 /dev/md0 /dev/sd[bc] # pvcreate /dev/md0 /dev/md0 sysfs attr level not in expected format: linear Physical volume "/dev/md0" successfully created Note that --rounding is overloaded od "chunk" parameter, from mdadm --rounding= Specify rounding factor for a Linear array. The size of each component will be rounded down to a multiple of this size. This is a synonym for --chunk but highlights the different meaning for Linear as compared to other RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in use, and is 0K (i.e. no rounding) in later kernels. So we should ignore chunk value for anything else than "raidX" MD personality.
Patch is here https://www.redhat.com/archives/lvm-devel/2011-July/msg00029.html
Committed upstream in 2.02.86, rebase for 5.8 should pick this up. commit 566939185eb01ef0f88151720e2c6b0106370833 Author: Milan Broz <mbroz@redhat.com> Date: Fri Jul 8 15:53:59 2011 +0000 Fix warning for pvcreate over MD linear. If MD linear device has set rounding (overload chunk size attribute), the pvcreate command prints this warning: /dev/md0 sysfs attr level not in expected format: linear diff --git a/WHATS_NEW b/WHATS_NEW index 9962fdf..18ed33e 100644 --- a/WHATS_NEW +++ b/WHATS_NEW @@ -1,5 +1,6 @@ Version 2.02.86 - ================================= + Fix warning in pvcreate for MD linear devices. NOTE: whats new message was refactored as follows: Version 2.02.86 - 8th July 2011 =============================== Remove unnecessary warning in pvcreate for MD linear devices.
Fixed in lvm2-2.02.88-1.el5.
Fix verified in the latest rpms. 2.6.18-274.el5 lvm2-2.02.88-4.el5 BUILT: Wed Nov 16 09:40:55 CST 2011 lvm2-cluster-2.02.88-4.el5 BUILT: Wed Nov 16 09:46:51 CST 2011 device-mapper-1.02.67-2.el5 BUILT: Mon Oct 17 08:31:56 CDT 2011 device-mapper-event-1.02.67-2.el5 BUILT: Mon Oct 17 08:31:56 CDT 2011 cmirror-1.1.39-10.el5 BUILT: Wed Sep 8 16:32:05 CDT 2010 kmod-cmirror-0.1.22-3.el5 BUILT: Tue Dec 22 13:39:47 CST 2009 [root@grant-01 ~]# mdadm --create /dev/md0 -c 32 -l linear -f -n1 /dev/sdc1 mdadm: array /dev/md0 started. [root@grant-01 ~]# pvcreate /dev/md0 Writing physical volume data to disk "/dev/md0" Physical volume "/dev/md0" successfully created
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-2012-0161.html