qemu-img permission denied on vmdk creation on CIFS share

[Hgkamath]

- on a CIFS mount qemu-img claims not to have permissions to write into a file.
- VMDK sparse file creation succeeds
- VMDK Flat file creation create the flat-file, but fails to write the description-file
- VMDK flat file creation succeeds on native linux mount such as ~/tmp or /tmp
- same effect as root or non-root
- same effect with selinux setenforce 0

a) I would have expected that the monolithic flat would have created only one large file just like sparse, but it seems to create a description file, in addition to the storing file.
b) I am aware that qemu-img may have problem opening very large files on CIFS, however, this file is not very large

Windows-10 latest updated 2004 19041.388
Linux VM, Fedora-32 in Virtualbox 6.1.12
# rpm -qa | grep qemu-img
qemu-img-4.2.0-7.fc32.x86_64

mount options:
mount -t cifs //10.x,x,x/$shname /mnt/hshare -o defaults,username=gana,rw,uid=1000,gid=1000,vers=3.0

[root@fedora ~]# cd /mnt/hshare/some/folder/createvmdk/
[root@fedora createvmdk]# qemu-img create -f vmdk test1.vmdk 100M -o subformat=monolithicFlat
Formatting 'test1.vmdk', fmt=vmdk size=104857600 compat6=off hwversion=undefined subformat=monolithicFlat
qemu-img: test1.vmdk: Could not write description: Permission denied
[root@fedora createvmdk]# ls -l test1*.*
-rwxr-xr-x. 1 gana gana 104857600 Jul 26 23:02 test1-flat.vmdk
-rwxr-xr-x. 1 gana gana 0 Jul 26 23:02 test1.vmdk
[root@fedora createvmdk]# du -k test1*.*
0 test1-flat.vmdk
0 test1.vmdk
# (doesn't seem to be really flat)

creation in /tmp works
# cd /tmp
[root@fedora tmp]# qemu-img create -f vmdk test1.vmdk 100M -o subformat=monolithicFlat
Formatting 'test1.vmdk', fmt=vmdk size=104857600 compat6=off hwversion=undefined subformat=monolithicFlat
[root@fedora tmp]# ls -l /tmp/test1*.*
-rw-r--r--. 1 root root 104857600 Jul 26 22:43 /tmp/test1-flat.vmdk
-rw-r--r--. 1 root root 313 Jul 26 22:43 /tmp/test1.vmdk
[root@fedora createvmdk]# du -k /tmp/test1*.*
4 /tmp/test1-flat.vmdk
4 /tmp/test1.vmdk

[root@fedora createvmdk]# cat /tmp/test1.vmdk
# Disk DescriptorFile
version=1
CID=5f13c13d
parentCID=ffffffff
createType="monolithicFlat"

# Extent description
RW 204800 FLAT "test1-flat.vmdk" 0

# The Disk Data Base
#DDB

ddb.virtualHWVersion = "4"
ddb.geometry.cylinders = "203"
ddb.geometry.heads = "16"
ddb.geometry.sectors = "63"
ddb.adapterType = "ide"

On the other-hand creating a sparse file works
cd /mnt/hshare/some/folder/createvmdk/
[root@fedora createvmdk]# qemu-img create -f vmdk test2.vmdk 100M -o subformat=monolithicSparse
Formatting 'test2.vmdk', fmt=vmdk size=104857600 compat6=off hwversion=undefined subformat=monolithicSparse
[root@fedora createvmdk]# ls l test2*.*
-rwxr-xr-x. 1 gana gana 65536 Jul 26 22:52 test2.vmdk
[root@fedora createvmdk]# du -k /tmp/test2*.*
12 /tmp/test2.vmdk

test2.vmdk is a binary file
inside it, located among garbled ascii characters is an embedded VMDK description
````
# Disk DescriptorFile
version=1
CID=cf302a20
parentCID=ffffffff
createType="monolithicSparse"

# Extent description
RW 204800 SPARSE "test2.vmdk"

# The Disk Data Base
#DDB

ddb.virtualHWVersion = "4"
ddb.geometry.cylinders = "203"
ddb.geometry.heads = "16"
ddb.geometry.sectors = "63"
ddb.adapterType = "ide"
```

[Hgkamath (hgkamath)]

I retract comment "a)I would have expected that the monolithic flat would have created only one large file just like sparse, but it seems to create a description file, in addition to the storing file."

pdf vmdk_specs-1.pdf "Virtual Disk Format 1.1" (https://www.vmware.com/app/vmdk/?src=vmdk) on page 7, line-34, a note is mentioned that says that is just how it is.
"A virtual disk described as monolithic and flat consists of two files. One file contains the descriptor. The other file is the extent used to store virtual machine data"

[Thomas Huth (th-huth)]

The QEMU project is currently moving its bug tracking to another system.
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If the bug has already been fixed in the latest upstream version of QEMU,
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[Launchpad Janitor (janitor)]

[Expired for QEMU because there has been no activity for 60 days.]