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[Qemu-devel] [RFC] A more consistent qemu-img create with a relative pat
From: |
Uri Lublin |
Subject: |
[Qemu-devel] [RFC] A more consistent qemu-img create with a relative path backing file |
Date: |
Mon, 26 Jan 2009 12:03:58 +0200 |
User-agent: |
Thunderbird 2.0.0.19 (X11/20090105) |
Hello,
Currently there is a difference in the way "qemu-img create -b" opens a backing
file and the way bdrv_open does that, when the backing file path is relative.
The former calculates the relative path from the CWD, while the latter
calculates the relative path from the filename's directory. This inconsistency
force the user to change-dir into the created-file directory when creating a new
image.
For example, let the backing file be <images>/dir1/g1.qcow2
and let image to be created be <images>/dir2/g2.qcow2, the steps I need to
take are:
1. cd <images>/dir2
2. qemu-img create -b ../dir1/g1.qcow2 -f qcow2 g2.qcow2
3. cd -
If I skip step 1 then both following options fail (let my CWD be e.g <images>)
a. qemu-img create -b ../dir1/g1.qcow2 -f qcow2 dir2/g2.qcow2 or
b. qemu-img create -b dir1/g1.qcow2 -f qcow2 dir2/g2.qcow
Option (a) fails to open the backing file and "qemu-img create" fails
Option (b) "qemu-img create" succeeds, but bdrv_open fails (e.g. "qemu-img info
dir2/g2.qcow"), as the backing file path calculation result in
<images>/dir2/dir1/g1.qcow2.
We suggest that the path calculation (full path from relative) will be done the
same for qemu-img create and for qemu-img info (bdrv_open), making their
behavior consistent. Thus qemu-img create will first calculate the backing file
path relative to the created-file path (using path_combine), making (1)+(2)+(3)
and (a) above the same.
In order to keep current behavior working, we suggest adding a new flag (-s or
-r) to qemu-img create for the new suggested behavior.
Would such a patch be acceptable ?
Thanks,
Uri.
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