[Qemu-devel] [Bug 1599539] Re: 2.6.0: vvfat driver generates bad FAT entries

[felix]

I noticed another bug in vvfat disk image generation. Applying the patch
I attached earlier made testing easier. I'm less sure what the actual
problem is.

Steps to reproduce (you'll need to have cpio, md5sum and GNU GRUB 2.x 
installed):
0. Apply the patch and build qemu-img.
1. Create a directory, cd into it and unpack the attached cpio file.
2. Run: qemu-img convert fat:. ../xxx.img
3. Run: for fname in $(grub-fstest ../xxx.img ls '(loop0,msdos1)/'); do 
grub-fstest ../xxx.img cat "(loop0,msdos1)/$fname" | md5sum | sed -e 
"s,-,$fname,"; done | md5sum -c
4. Observe how almost all checksum tests fail.

Alternatively, the image can be tested inside a virtual machine. You
probably get the idea.

(File names and data have been changed for the sake of anonymity and
better compressibility)

** Attachment added: "Bug-triggering file structure"
   
https://bugs.launchpad.net/qemu/+bug/1599539/+attachment/4707220/+files/xxx.cpio.xz

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https://bugs.launchpad.net/bugs/1599539

Title:
  2.6.0: vvfat driver generates bad FAT entries

Status in QEMU:
  New

Bug description:
  The vvfat driver sometimes generates entries about which file system
  checking utilities generate complaints.

  For example, dosfsck will complain that the volume label entry has
  non-zero size. ScanDisk from Windows 9x complains about invalid dot
  (".") and dot-dot ("..") entries in directories and also about invalid
  long file name entries. MS-DOS ScanDisk also often manages to find
  "lost clusters" on the drive.

  Tangentially: qemu-img convert fat:test test.img doesn't seem to work
  -- it generates an 504MiB of zero bytes and hangs. qemu-img map
  fat:test generates an assertion failure. Having qemu-img working might
  have helped with debugging the above issue.

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