colin/nixpkgs
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

nixos/qemu-vm: Allow building a Nix store image instead of using 9p

Browse Source 
Add the `useNixStoreImage` option, allowing a disk image with the
necessary contents from the Nix store to be built using
make-disk-image.nix. The image will be mounted at `/nix/store` and
acts as a drop-in replacement for the usual 9p mounting of the host's
Nix store.

This removes the performance penalty of 9p, drastically improving
execution speed of applications which do lots of reads from the Nix
store. The caveats are increased disk space usage and image build
time.
This commit is contained in:
talyz 2021-10-05 22:32:56 +02:00 committed by Yuka
parent 87d8eec069
commit 84839b395f
1 changed files with 56 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

59
nixos/modules/virtualisation/qemu-vm.nix
View File

@ -122,6 +122,12 @@ let
TMPDIR=$(mktemp -d nix-vm.XXXXXXXXXX --tmpdir)
fi
${lib.optionalString cfg.useNixStoreImage
''
# Create a writable copy/snapshot of the store image.
${qemu}/bin/qemu-img create -f qcow2 -F qcow2 -b ${storeImage}/nixos.qcow2 "$TMPDIR"/store.img
''}
# Create a directory for exchanging data with the VM.
mkdir -p "$TMPDIR/xchg"
@ -263,6 +269,18 @@ let
'' # */
);
storeImage = import ../../lib/make-disk-image.nix {
inherit pkgs config lib;
additionalPaths = [ regInfo ];
format = "qcow2";
onlyNixStore = true;
partitionTableType = "none";
installBootLoader = false;
diskSize = "auto";
additionalSpace = "0M";
copyChannel = false;
};
in
{
@ -608,6 +626,20 @@ in
};
};
virtualisation.useNixStoreImage =
mkOption {
type = types.bool;
default = false;
description = ''
Build and use a disk image for the Nix store, instead of
accessing the host's one through 9p.
For applications which do a lot of reads from the store,
this can drastically improve performance, but at the cost of
disk space and image build time.
'';
};
virtualisation.useBootLoader =
mkOption {
type = types.bool;
@ -762,9 +794,18 @@ in
virtualisation.pathsInNixDB = [ config.system.build.toplevel ];
virtualisation.sharedDirectories = {
nix-store = { source = "/nix/store"; target = "/nix/store"; };
xchg = { source = ''"$TMPDIR"/xchg''; target = "/tmp/xchg"; };
shared = { source = ''"''${SHARED_DIR:-$TMPDIR/xchg}"''; target = "/tmp/shared"; };
nix-store = mkIf (!cfg.useNixStoreImage) {
source = builtins.storeDir;
target = "/nix/store";
};
xchg = {
source = ''"$TMPDIR"/xchg'';
target = "/tmp/xchg";
};
shared = {
source = ''"''${SHARED_DIR:-$TMPDIR/xchg}"'';
target = "/tmp/shared";
};
};
virtualisation.qemu.networkingOptions =
@ -815,6 +856,11 @@ in
driveExtraOpts.cache = "writeback";
driveExtraOpts.werror = "report";
}]
(mkIf cfg.useNixStoreImage [{
name = "nix-store";
file = ''"$TMPDIR"/store.img'';
deviceExtraOpts.bootindex = if cfg.useBootLoader then "3" else "2";
}])
(mkIf cfg.useBootLoader [
# The order of this list determines the device names, see
# note [Disk layout with `useBootLoader`].
@ -865,6 +911,13 @@ in
options = [ "mode=1777" "strictatime" "nosuid" "nodev" "size=${toString config.boot.tmpOnTmpfsSize}" ];
};
"/nix/${if cfg.writableStore then ".ro-store" else "store"}" =
mkIf cfg.useNixStoreImage
{ device = "${lookupDriveDeviceName "nix-store" cfg.qemu.drives}";
neededForBoot = true;
options = [ "ro" ];
};
"/nix/.rw-store" = mkIf (cfg.writableStore && cfg.writableStoreUseTmpfs)
{ fsType = "tmpfs";
options = [ "mode=0755" ];