hst/fs: implement overlay fstype

This finally exposes overlay mounts in the high level hakurei API.

Signed-off-by: Ophestra <cat@gensokyo.uk>

test/sandbox/case/device.nix

@@ -47,7 +47,10 @@ in
     ];
 
     fs = fs "dead" {
-      ".hakurei" = fs "800001ed" { } null;
+      ".hakurei" = fs "800001ed" {
+        ".ro-store" = fs "801001fd" null null;
+        store = fs "800001ff" null null;
+      } null;
       bin = fs "800001ed" { sh = fs "80001ff" null null; } null;
       dev = fs "800001ed" null null;
       etc = fs "800001ed" {
@@ -218,6 +221,8 @@ in
       (ent "/devices" "/sys/devices" "ro,nosuid,nodev,noexec,relatime" "sysfs" "sysfs" "rw")
       (ent "/dri" "/dev/dri" "rw,nosuid" "devtmpfs" "devtmpfs" ignore)
       (ent "/var/cache" "/var/cache" "rw,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
+      (ent "/" "/.hakurei/.ro-store" "rw,relatime" "overlay" "overlay" "ro,lowerdir=/host/nix/.ro-store:/host/nix/.rw-store/upper,redirect_dir=nofollow,userxattr")
+      (ent "/" "/.hakurei/store" "rw,relatime" "overlay" "overlay" "rw,lowerdir=/host/nix/.ro-store:/host/nix/.rw-store/upper,upperdir=/host/tmp/.hakurei-store-rw/upper,workdir=/host/tmp/.hakurei-store-rw/work,redirect_dir=nofollow,userxattr")
       (ent "/etc" ignore "ro,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
       (ent "/" "/run/user" "rw,nosuid,nodev,relatime" "tmpfs" "ephemeral" "rw,size=4k,mode=755,uid=1000004,gid=1000004")
       (ent "/tmp/hakurei.1000/runtime/4" "/run/user/65534" "rw,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")

test/sandbox/case/mapuid.nix

@@ -56,7 +56,10 @@ in
     ];
 
     fs = fs "dead" {
-      ".hakurei" = fs "800001ed" { } null;
+      ".hakurei" = fs "800001ed" {
+        ".ro-store" = fs "801001fd" null null;
+        store = fs "800001ff" null null;
+      } null;
       bin = fs "800001ed" { sh = fs "80001ff" null null; } null;
       dev = fs "800001ed" {
         core = fs "80001ff" null null;
@@ -248,6 +251,8 @@ in
       (ent "/devices" "/sys/devices" "ro,nosuid,nodev,noexec,relatime" "sysfs" "sysfs" "rw")
       (ent "/dri" "/dev/dri" "rw,nosuid" "devtmpfs" "devtmpfs" ignore)
       (ent "/var/cache" "/var/cache" "rw,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
+      (ent "/" "/.hakurei/.ro-store" "rw,relatime" "overlay" "overlay" "ro,lowerdir=/host/nix/.ro-store:/host/nix/.rw-store/upper,redirect_dir=nofollow,userxattr")
+      (ent "/" "/.hakurei/store" "rw,relatime" "overlay" "overlay" "rw,lowerdir=/host/nix/.ro-store:/host/nix/.rw-store/upper,upperdir=/host/tmp/.hakurei-store-rw/upper,workdir=/host/tmp/.hakurei-store-rw/work,redirect_dir=nofollow,userxattr")
       (ent "/etc" ignore "ro,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
       (ent "/" "/run/user" "rw,nosuid,nodev,relatime" "tmpfs" "ephemeral" "rw,size=4k,mode=755,uid=1000003,gid=1000003")
       (ent "/tmp/hakurei.1000/runtime/3" "/run/user/1000" "rw,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")

test/sandbox/case/tty.nix

@@ -56,7 +56,10 @@ in
     ];
 
     fs = fs "dead" {
-      ".hakurei" = fs "800001ed" { } null;
+      ".hakurei" = fs "800001ed" {
+        ".ro-store" = fs "801001fd" null null;
+        store = fs "800001ff" null null;
+      } null;
       bin = fs "800001ed" { sh = fs "80001ff" null null; } null;
       dev = fs "800001ed" {
         console = fs "4200190" null null;
@@ -250,6 +253,8 @@ in
       (ent "/devices" "/sys/devices" "ro,nosuid,nodev,noexec,relatime" "sysfs" "sysfs" "rw")
       (ent "/dri" "/dev/dri" "rw,nosuid" "devtmpfs" "devtmpfs" ignore)
       (ent "/var/cache" "/var/cache" "rw,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
+      (ent "/" "/.hakurei/.ro-store" "rw,relatime" "overlay" "overlay" "ro,lowerdir=/host/nix/.ro-store:/host/nix/.rw-store/upper,redirect_dir=nofollow,userxattr")
+      (ent "/" "/.hakurei/store" "rw,relatime" "overlay" "overlay" "rw,lowerdir=/host/nix/.ro-store:/host/nix/.rw-store/upper,upperdir=/host/tmp/.hakurei-store-rw/upper,workdir=/host/tmp/.hakurei-store-rw/work,redirect_dir=nofollow,uuid=on,userxattr")
       (ent "/etc" ignore "ro,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")
       (ent "/" "/run/user" "rw,nosuid,nodev,relatime" "tmpfs" "ephemeral" "rw,size=4k,mode=755,uid=1000002,gid=1000002")
       (ent "/tmp/hakurei.1000/runtime/2" "/run/user/65534" "rw,nosuid,nodev,relatime" "ext4" "/dev/disk/by-label/nixos" "rw")

test/sandbox/configuration.nix

@@ -82,6 +82,24 @@ in
         src = "/var/cache";
         write = true;
       }
+      {
+        type = "overlay";
+        dst = "/.hakurei/.ro-store";
+        lower = [
+          "/nix/.ro-store"
+          "/nix/.rw-store/upper"
+        ];
+      }
+      {
+        type = "overlay";
+        dst = "/.hakurei/store";
+        lower = [
+          "/nix/.ro-store"
+          "/nix/.rw-store/upper"
+        ];
+        upper = "/tmp/.hakurei-store-rw/upper";
+        work = "/tmp/.hakurei-store-rw/work";
+      }
     ];
 
     inherit (testCases) apps;

test/sandbox/test.py

@@ -55,6 +55,7 @@ print(machine.fail("sudo -u alice -i hakurei run capsh --has-p=CAP_SYS_ADMIN"))
 print(machine.fail("sudo -u alice -i hakurei run umount -R /dev"))
 
 # Check sandbox outcome:
+machine.succeed("install -dm0777 /tmp/.hakurei-store-rw/{upper,work}")
 check_offset = 0
 def check_sandbox(name):
     global check_offset