[Bug 1889033] Re: qemu-img permission denied on vmdk creation on CIFS share

[Hgkamath <1889033@bugs.launchpad.net>]

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"

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https://bugs.launchpad.net/bugs/1889033

Title:
  qemu-img permission denied on vmdk creation on CIFS share

Status in QEMU:
  New

Bug description:
  
  - 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"
  ```

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