[Bug 1091430] Re: 9p fails with readonly+non-root due to O_NOATIME

[Serge Hallyn]

** Description changed:

  http://lists.gnu.org/archive/html/qemu-devel/2012-01/msg02053.html
  
  Upstream QEMU commit: eed968607d656a218712df47a5e0432c21fd6994
  hw/9pfs: Remove O_NOATIME flag from 9pfs open() calls in readonly mode
  
  When a 9p filesystem is exported with the readonly flag, QEMU adds the
  O_NOATIME flag to all accesses. This causes all reads to fail when qemu
  is run as non-root and the runas user doesn't own the files being
  accessed. The patch is a one-liner; please add it to the distribution
  patches.
  
  Steps to reproduce:
  1. Download ubuntu-12.04.1-desktop-amd64.iso
  2. As a non-root user,
  
  $ mkdir testdir
  $ echo "value" > testdir/testfile
  $ sudo chown -R root:root testdir
  
  3. Start the VM, again as a non-root user:
  
  $ qemu-system-x86_64 -cdrom /path/to/ubuntu-12.04.1-desktop-amd64.iso -vga std -m 2048 \
  -fsdev local,id=foo,path=testdir,security_model=none,readonly \
  -device virtio-9p-pci,fsdev=foo,mount_tag=foo
  
  4. Inside the VM, select "Try Ubuntu", open a terminal, and run:
  
  $ sudo mount -t 9p -o trans=virtio,version=9p2000.L,ro foo /mnt
  $ ls /mnt
  testfile
  $ cat /mnt/testfile
  
  Expected results:
  value
  
  Actual results:
  cat: /mnt/testfile: operation not permitted
+ 
+ =======================
+ SRU Justification:
+ 1. Impact: cannot use 9p fs in ro mode as nonroot.
+ 2. Development fix: a patch upstream fixes the attempt to use a flag which only root may use (when not needed)
+ 3. Stable fix: cherrypick of development fix
+ 4. Test case: detailed above
+ 5. Regression potential: this patch only affects 9pfs, and is cherrypicked from upstream, so should have no adverse effect on any other qemu code.
+ ======================

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https://bugs.launchpad.net/bugs/1091430

Title:
  9p fails with readonly+non-root due to O_NOATIME

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