Ubuntu Image

Please use os.truncate() instead of dd when creating the file

Bug #1619351 reported by Michael Vogt
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Ubuntu Image
Invalid
Undecided
Unassigned

Bug Description

The current use of "dd" to create the image means that a real 4gb file is created. The previous ubuntu-device-flash would use a sparse file for this. This is important for the snappy project because we take the image, load it into ram and write it to a test machine to do the testing of the actual machine. However this only works if the file fits in ram. with a sparse file it does, with a real 4gb file it does not.

I started working on this but got stuck in mkfs.ext4 not creating a partition apparently.

Revision history for this message
Steve Langasek (vorlon) wrote :

We should switch to native Python operations wherever feasible, but I can't see the problem you're describing. I've tested the sparseness at every stage and while ls shows a 4GB image, du consistently shows it occupying 300M on disk. What are you seeing that suggests this is not sparse?

Revision history for this message
Mathieu Trudel-Lapierre (cyphermox) wrote :

Things look fine to me too; the file is indeed a sparse file:

[14:13:55] mtrudel@demeter:~git $ ls -latr
total 417584
[...]
drwxrwxr-x 53 mtrudel mtrudel 4096 sep 1 12:45 ./
-rw-rw-r-- 1 mtrudel mtrudel 4000000000 sep 1 12:48 toto.img
drwxrwxr-x 9 mtrudel mtrudel 4096 sep 1 14:05 ubuntu-image/
[14:13:56] mtrudel@demeter:~git $ du -hs toto.img
396M toto.img

Changed in ubuntu-image:
status: New → Incomplete
Revision history for this message
Barry Warsaw (barry) wrote :

See also the discussion in LP: #1619362 although I'm not going to dupe this bug to that one.

summary: - Please use os.trunacte() instead of dd when creating the file
+ Please use os.truncate() instead of dd when creating the file
Revision history for this message
Michael Vogt (mvo) wrote :

This is fixed with the latest master.

Changed in ubuntu-image:
status: Incomplete → Fix Committed
Revision history for this message
Michael Vogt (mvo) wrote :

Fwiw, I think what happend to me was exactly the cross-device copy. When testing my "fix" I used a named working directory to inspect things and stuff magically works. So sorry for the incorrect report.

Changed in ubuntu-image:
status: Fix Committed → Invalid
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