info does not recognize file format of vpc with subformat=fixed

[Scott Moser]

After creating or converting an image to vpc with 'subformat=fixed'
'qemu-img info' incorrectly identifies the image as 'raw' format.

$ qemu-img --version
qemu-img version 2.11.1(Debian 1:2.11+dfsg-1ubuntu7.10)
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers

$ qemu-img create -f vpc -o subformat=fixed my.vpc 2G
Formatting 'my.vpc', fmt=vpc size=2147483648 subformat=fixed

$ qemu-img info my.vpc
image: my.vpc
file format: raw
virtual size: 2.0G (2147992064 bytes)
disk size: 4.0K

$ qemu-img info -f vpc my.vpc
image: my.vpc
file format: vpc
virtual size: 2.0G (2147991552 bytes)
disk size: 4.0K

[Scott Moser (smoser)]

$ ./go-create
#version: 2.11.1
qcow: PASS fmt=qcow auto=qcow exp=qcow [name=my-img.qcow opts=]
qcow2: PASS fmt=qcow2 auto=qcow2 exp=qcow2 [name=my-img.qcow2 opts=]
qed: PASS fmt=qed auto=qed exp=qed [name=my-img.qed opts=]
raw: PASS fmt=raw auto=raw exp=raw [name=my-img.raw opts=]
vdi: PASS fmt=vdi auto=vdi exp=vdi [name=my-img.vdi opts=]
vhdx: PASS fmt=vhdx auto=vhdx exp=vhdx [name=my-img.vhdx opts=]
vmdk: PASS fmt=vmdk auto=vmdk exp=vmdk [name=my-img.vmdk opts=]
vpc: PASS fmt=vpc auto=vpc exp=vpc [name=my-img.vpc opts=]
vpc-fixed: FAIL fmt=vpc auto=raw exp=vpc [name=my-img.vpc-fixed opts=-o subformat=fixed]
vpc-fforce: FAIL fmt=vpc auto=raw exp=vpc [name=my-img.vpc-fforce opts=-o subformat=fixed,force_size]
FAIL [2]

[John Snow (jnsnow)]

Well, 2.11 is way too old, but it still does reproduce on the latest development head.

[Thomas Huth (th-huth)]

Suggested patch:
https://lists.gnu.org/archive/html/qemu-devel/2021-03/msg09422.html

[Scott Moser (smoser)]

@Thomas,

Is there really no way to detect the format other than relying on extension? :-(

[Thomas Huth (th-huth)]

@smoser : fixed-size VHD images don't have a header, and there is AFAIK currently no way for probing a footer in the QEMU code, so relying on the extension seems to be the only way right now, as far as I can tell.

[Thomas Huth (th-huth)]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/559