[Bug 1336794] Re: 9pfs does not honor open file handles on unlinked files

[Thomas Huth <1336794@bugs.launchpad.net>]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/103


** Changed in: qemu
       Status: Confirmed => Expired

** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #103
   https://gitlab.com/qemu-project/qemu/-/issues/103

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https://bugs.launchpad.net/bugs/1336794

Title:
  9pfs does not honor open file handles on unlinked files

Status in QEMU:
  Expired
Status in Ubuntu:
  Confirmed

Bug description:
  This was originally filed over here:
  https://bugzilla.redhat.com/show_bug.cgi?id=1114221

  The open-unlink-fstat idiom used in some places to create an anonymous
  private temporary file does not work in a QEMU guest over a virtio-9p
  filesystem.

  Version-Release number of selected component (if applicable):

  qemu-kvm-1.6.2-6.fc20.x86_64
  qemu-system-x86-1.6.2-6.fc20.x86_64
  (those are fedora RPMs)

  How reproducible:

  Always. See this example C program:

  https://bugzilla.redhat.com/attachment.cgi?id=913069

  Steps to Reproduce:
  1. Export a filesystem with virt-manager for the guest.
        (type: mount, driver: default, mode: passthrough)
  2. Start guest and mount that filesystem
        (mount -t 9p -o trans=virtio,version=9p2000.L  ...)
  3. Run a program that uses open-unlink-fstat
        (in my case it was trying to compile Perl 5.20)

  Actual results:

  fstat fails:

  open("/home/tst/filename", O_RDWR|O_CREAT|O_EXCL, 0600) = 3
  unlink("/home/tst/filename")            = 0
  fstat(3, 0x23aa1a8)                     = -1 ENOENT (No such file or directory)
  close(3)

  Expected results:

  open("/home/tst/filename", O_RDWR|O_CREAT|O_EXCL, 0600) = 3
  unlink("/home/tst/filename")            = 0
  fstat(3, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0
  fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
  close(3) 

  Additional info:

  There was a patch put into the kernel back in '07 to handle this very
  problem for other filesystems; maybe its helpful:

        http://lwn.net/Articles/251228/

  There is also a thread on LKML from last December specifically about
  this very problem:

        https://lkml.org/lkml/2013/12/31/163

  There was a discussion on the QEMU list back in '11 that doesn't seem
  to have come to a conclusion, but did provide the test program that
  i've attached to this report:

        http://marc.info/?l=qemu-devel&m=130443605720648&w=2

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