[Bug 1854878] Re: Physical USB thumbdrive treated as read-only

[Thomas Huth]

The QEMU project is currently considering to move its bug tracking to
another system. For this we need to know which bugs are still valid
and which could be closed already. Thus we are setting older bugs to
"Incomplete" now.

If you still think this bug report here is valid, then please switch
the state back to "New" within the next 60 days, otherwise this report
will be marked as "Expired". Or please mark it as "Fix Released" if
the problem has been solved with a newer version of QEMU already.

Thank you and sorry for the inconvenience.


** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1854878

Title:
  Physical USB thumbdrive treated as read-only

Status in QEMU:
  Incomplete

Bug description:
  So I have installed FreeDOS on my USB thumbdrive, by using Rufus.
  Everything goes as expected so far. That's good.

  When I run QEMU with this command line:
  qemu-system-x86_64.exe -drive file=\\.\PhysicalDrive1

  it of course is read-only, just like the resulting console message says:
  WARNING: Image format was not specified for '\\.\PhysicalDrive1' and probing 
guessed raw.
           Automatically detecting the format is dangerous for raw images, 
write operations on block 0 will be restricted.
           Specify the 'raw' format explicitly to remove the restrictions.

  
  So what I then did, was I ran QEMU with this command line:
  qemu-system-x86_64.exe -drive file=\\.\PhysicalDrive1,format=raw

  As expected, the above mentioned console message no longer appears.
  However, beyond that, QEMU doesn't behave as it should regarding read-only 
status. When I try any operation that involves writing to the drive, it becomes 
quite clear that the drive is still read-only. Any writing operations to the 
drive result in FreeDOS giving me the error message:
  Error writing to drive C: DOS area: sector not found.

  The above situation is clearly a bug. QEMU should not be treating it
  as read-only once I specify format=raw.

  Note that drive C is how the guest OS refers to the USB thumbdrive
  (it's drive E in my host OS, and drive C in my host OS is the actual
  system drive).

  And yes, it is a QEMU bug. It's not a FreeDOS bug I tested it with this 
command line, so that all changes would be written to a temporary snapshot file:
  qemu-system-x86_64.exe -drive file=\\.\PhysicalDrive1,format=raw,snapshot
  That last drive option "snapshot" tells QEMU to create a temporary snapshot 
file, and to write all changes to that. When I do that, all write operations 
are successful. So it seems that there is a bug in QEMU where it keeps 
read-only mode in place for a physical drive, even when format=raw is 
specified. Please fix this bug. Thanks in advance.

  Here's my current setup.
  Host OS: Windows 10 (64bit)
  Guest OS: FreeDOS
  QEMU version: 4.1.0

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