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

[felix]

I believe commits f82d92bb028a1d674bab4ccc7e6cde6c04956230 and
6817efea3a0d1bf87be815970cdb014c5a64b628 have fixed this particular bug;
although I've since noticed the vvfat driver remains quite fragile,
especially FAT32 and writing support. I've got some patches for it of my
own, which I might submit someday (they aren't quite ready yet).

Also, after some testing, it turns one can simply grow the fixed-size
root directory table above 512 entries, and it doesn't seem to actually
cause any problems after all; although I haven't tested any extreme
cases or obscure implementations. Shrinking it (entry-wise) should be
fine in any case: 1440 KiB floppy disks typically allow 224 root
directory entries, which is 14 clusters = 14 sectors.

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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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