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Bug 1082630 - Remove limitations on maximum number of snapshots in an image chain, due to backing file and filename character lengths
Summary: Remove limitations on maximum number of snapshots in an image chain, due to b...
Keywords:
Status: CLOSED WONTFIX
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: qemu-kvm-rhev
Version: 7.1
Hardware: x86_64
OS: Linux
unspecified
medium
Target Milestone: rc
: ---
Assignee: Jeff Cody
QA Contact: Virtualization Bugs
URL:
Whiteboard:
: 1186989 (view as bug list)
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2014-03-31 14:01 UTC by Gordon Watson
Modified: 2019-11-14 06:26 UTC (History)
12 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2016-06-30 17:23:13 UTC
Target Upstream Version:
Embargoed:


Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Knowledge Base (Article) 730773 0 None None None 2018-12-05 19:08:24 UTC

Comment 1 Jeff Cody 2014-04-01 03:20:30 UTC
Additional information:  internally, the backing file chain is may be put together by the concatenation of many pathname strings, if the filename paths are relative paths.  If this exceeds PATH_MAX (4096 under RHEL), then we will fail to either open or create snapshot images.

Note that this is not necessarily the same as the filename character limit found in the image header (e.g., the header in a qcow2 file).  While if that is too long we may have similar issues, the backing file character length issue is different because the block layer builds up the backing file pathname string dynamically on image open.

See BZ 1067576 for more information, as well as for steps on how to replicate the issue (attachment #867573 [details]).

The final long-term solution is likely to be dynamically allocating backing file and filename strings internally, and perhaps also flattening redundant relative pathname strings.

Comment 2 Jeff Cody 2014-11-05 19:42:32 UTC
Moving to 7.2 - this is for the long-term solution, whereas BZ 1117170 is for the more immediate term solution for 7.1  This is also a RHEV bug, instead of a RHEL bug.

Comment 5 Jeff Cody 2016-03-23 19:26:51 UTC
*** Bug 1186989 has been marked as a duplicate of this bug. ***

Comment 6 Germano Veit Michel 2016-06-16 03:00:00 UTC
Does BZ 1333627 also fixes this?

That is, replacing "../<img>/<vol>" with "<vol>" in backing file field of qcow2 header.

https://gerrit.ovirt.org/#/c/57284/

Comment 7 Adam Litke 2016-06-27 14:35:38 UTC
(In reply to Germano Veit Michel from comment #6)
> Does BZ 1333627 also fixes this?
> 
> That is, replacing "../<img>/<vol>" with "<vol>" in backing file field of
> qcow2 header.
> 
> https://gerrit.ovirt.org/#/c/57284/

It mitigates the need to make any changes in qemu so yes we can probably close this.

Comment 8 Jeff Cody 2016-06-30 17:23:13 UTC
Closing this (WONTFIX), per Comment #6 and Comment #7.  Fixing it in the upper layers so the condition doesn't occur is the proper solution, as well.


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