Note: This is a public test instance of Red Hat Bugzilla. The data contained within is a snapshot of the live data so any changes you make will not be reflected in the production Bugzilla. Email is disabled so feel free to test any aspect of the site that you want. File any problems you find or give feedback at bugzilla.redhat.com.
Bug 1804207 - Libguestfs relies on /dev/sdX device enumeration order, kernel no longer enumerates them in order
Summary: Libguestfs relies on /dev/sdX device enumeration order, kernel no longer enum...
Keywords:
Status: CLOSED UPSTREAM
Alias: None
Product: Virtualization Tools
Classification: Community
Component: libguestfs
Version: unspecified
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: ---
Assignee: Richard W.M. Jones
QA Contact:
URL:
Whiteboard:
: 1803191 (view as bug list)
Depends On:
Blocks: PYTHON39
TreeView+ depends on / blocked
 
Reported: 2020-02-18 12:57 UTC by Richard W.M. Jones
Modified: 2020-03-12 10:14 UTC (History)
5 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2020-03-12 10:14:17 UTC
Embargoed:

Attachments (Terms of Use)

Description Richard W.M. Jones 2020-02-18 12:57:38 UTC 
Description of problem:

In libguestfs, it's an unfortunate (in hindsight) ABI that we rely on
the order that /dev/sdX devices are enumerated being identical to the
order that the devices appear in the libvirt XML.  For example, that
the first device appears as /dev/sda, the second as /dev/sdb and so
on.

This was true until fairly recently.  What changed (in Linux) was
that it now does asynchronous polling:

- [drivers] driver core: Probe devices asynchronously instead of the driver
(Jeff Moyer) [1724965]
- [drivers] device core: Consolidate locking and unlocking of parent and device 
(Jeff Moyer) [1724965]
- [drivers] driver core: Establish order of operations for device_add and
device_del via bitflag (Jeff Moyer)
- [drivers] driver core: Add missing dev->bus->need_parent_lock checks (Jeff
Moyer) [1724965]
- [drivers] driver core: Move async_synchronize_full call (Jeff Moyer) [1724965]

This means that devices are no longer created in order, the
/dev/sdX name can change from boot to boot.

This also affects supermin when it's looking for the root
device (see bug 1803191 for an example).  I don't know yet if
we should file a separate bug for supermin.

Version-Release number of selected component (if applicable):

libguestfs 1.41.8

How reproducible:

Quite infrequent, but easier to reproduce if you add a large
number of disks (eg. > 100).

Steps to Reproduce:

We actually have a regression test that picks this up, see:

https://github.com/libguestfs/libguestfs/blob/56834875b25a604983b1aa90b15a01e6cc22c9bc/tests/disks/test-add-disks.c#L311

(Thanks Vitaly Kuznetsov for bug analysis)
Comment 1 Richard W.M. Jones 2020-02-18 12:59:47 UTC 
*** Bug 1803191 has been marked as a duplicate of this bug. ***
Comment 2 Richard W.M. Jones 2020-02-20 14:52:06 UTC 
First part of the fix is:
https://www.redhat.com/archives/libguestfs/2020-February/msg00220.html

This isn't quite the whole story.  It does appear that we will need to
either modify supermin or else modify libguestfs to supply the
root=UUID=XXX parameter to supermin.  See also this commit in supermin:
https://github.com/libguestfs/supermin/commit/cd5281beed0af7b57473e36f6fa275eaecde4f09
Comment 3 Richard W.M. Jones 2020-03-12 10:14:17 UTC 
This is upstream in:

https://github.com/libguestfs/libguestfs/commit/bca9b94fc593771b3801b09b95e477f160517909
https://github.com/libguestfs/libguestfs/commit/a06262e1998f0147886a8184c033453e09e0b9ec
https://github.com/libguestfs/libguestfs/commit/18c3f40c60080a8d0f7c30efe0553201cb5446e7

which is available in libguestfs 1.42.
Note You need to log in before you can comment on or make changes to this bug.