nixpkgs/pkgs/applications/virtualization/qemu/9p-ignore-noatime.patch

commit cdc3e7eeafa9f683214d2c15d52ef384c3de6611
Author: aszlig <aszlig@nix.build>
Date:   Mon Mar 18 13:21:01 2019 +0100

    9pfs: Ignore O_NOATIME open flag
    
    Since Linux 4.19, overlayfs uses the O_NOATIME flag on its lowerdir,
    which in turn causes errors when the Nix store is mounted in the guest
    because the file owner of the store paths typically don't match the
    owner of the QEMU process.
    
    After submitting a patch to the overlayfs mailing list[1], it turns out
    that my patch was incomplete[2] and needs a bit more rework.
    
    So instead of using an incomplete kernel patch in nixpkgs, which affects
    *all* users of overlayfs, not just NixOS VM tests, I decided that for
    now it's better to patch QEMU instead.
    
    The change here really only ignores the O_NOATIME flag so that the
    behaviour is similar to what NFS does. From open(2):
    
      This flag may not be effective on all filesystems. One example is NFS,
      where the server maintains the access time.
    
    This change is therefore only temporary until the final fix lands in the
    stable kernel releases.
    
    [1]: https://www.spinics.net/lists/linux-unionfs/msg06755.html
    [2]: https://www.spinics.net/lists/linux-unionfs/msg06756.html
    
    Signed-off-by: aszlig <aszlig@nix.build>

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 55821343e5..0b8425fe18 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -127,7 +127,6 @@ static int dotl_to_open_flags(int flags)
         { P9_DOTL_LARGEFILE, O_LARGEFILE },
         { P9_DOTL_DIRECTORY, O_DIRECTORY },
         { P9_DOTL_NOFOLLOW, O_NOFOLLOW },
-        { P9_DOTL_NOATIME, O_NOATIME },
         { P9_DOTL_SYNC, O_SYNC },
     };