Bug 449755

Summary:	RFE: file magic for LVM persistent overlay snapshots
Product:	[Fedora] Fedora	Reporter:	Jason Farrell <farrellj>
Component:	file	Assignee:	Tomas Smetana <tsmetana>
Status:	CLOSED RAWHIDE	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	low	Docs Contact:
Priority:	low
Version:	rawhide
Target Milestone:	---
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2008-06-06 11:50:49 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Jason Farrell 2008-06-03 12:48:43 UTC

Would be nice to get file magic added for LVM snapshots, especially now that the
persistent overlay image in Fedora 9 will be seen by more eyes. Having file
report that it's just "data" isn't very enlightening.

My ~/.magic:
-----------------------------------
# $ hexdump -C -n 512 /media/Patriot/LiveOS/overlay-Patriot-32B4-B464
# 00000000  53 6e 41 70 01 00 00 00  01 00 00 00 08 00 00 00  |SnAp............|
# 00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
# # hexdump -C -n 512 /dev/mapper/vgr0-0tmp--snap-cow
# 00000000  53 6e 41 70 01 00 00 00  01 00 00 00 08 00 00 00  |SnAp............|
# 00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|

# header struct: 
http://fxr.watson.org/fxr/source//drivers/md/dm-exception-store.c?v=linux-2.6#L53
# lelongs:  magic, valid flag, version, chunk_size in sectors
0    string  SnAp        LVM Snapshot (CopyOnWrite store)
>4   lelong    !0        - valid,
>4   lelong    0         - invalid,
>8   lelong    x         version = %d,
>12  lelong    x         chunk_size = %d
-----------------------------------

e.g.:
$ file /media/Patriot/LiveOS/overlay-Patriot-32B4-B464
/media/Patriot/LiveOS/overlay-Patriot-32B4-B464: LVM Snapshot (CopyOnWrite
store) - valid, version = 1, chunk_size = 8

Comment 1 Tomas Smetana 2008-06-03 13:00:15 UTC

Thanks.  This looks OK to me.  Have you sent your patch upstream as well?

Comment 2 Jason Farrell 2008-06-03 13:15:55 UTC

Only here. Not sure who the keeper of the upstream magic is

Comment 3 Tomas Smetana 2008-06-03 13:39:49 UTC

Nevermind. I'll send it to him together with other updates I have.