Add ROSETTA virtiofs directory share exposed to guest linux OS

README.md

@@ -1,3 +1,65 @@
+# Rosetta Support for Linux guests
+
+This fork adds a commandline option `-g <rosetta directory share tag>` to specify the name of the directory share tag
+used to expose the Rosetta virtiofs directory share to the arm64 Linux guest. The tag can be any name you choose so long
+as it conforms to virtiofs naming conventions.
+
+The virtiofs directory share contains a single linux/arm64 executable named `rosetta`. This executable is an amd64
+emulator which uses the native Rosetta functionality on MacOS to execute amd64 Linux binaries on the arm64 host
+running Apple Silicon.
+
+To actually make use of it in your arm64 Linux guest you must explicitly register a custom binfmt handler in the arm64
+Linux guest by following the installation steps below.
+
+Example usage of `vftool` with `-g ROSETTA`:
+```shell
+vftool/build/vftool -k vmlinux -i initrd -g ROSETTA -d root.img -d varlibdocker.img -m 8192 -p 6 -t 0 -a "root=/dev/vda" "$@"
+```
+
+## PREREQUISITES
+The `binfmt-support` Ubuntu package must be installed in the arm64 Linux guest; this package contains the required
+`update-binfmts` tool.
+```shell
+% sudo apt install binfmt-support
+```
+
+## INSTALLATION
+Run these commands in your arm64 Linux guest on every boot:
+```shell
+% mkdir /tmp/rosetta
+% sudo mount -t virtiofs ROSETTA /tmp/rosetta
+% sudo /usr/sbin/update-binfmts --install rosetta /tmp/rosetta/rosetta \
+    --magic "\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x3e\x00" \
+    --mask "\xff\xff\xff\xff\xff\xfe\xfe\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff" \
+    --credentials yes --preserve no --fix-binary yes
+```
+
+The token `ROSETTA` in the `mount` command above MUST MATCH the tag name given to vftool `-g` commandline option.
+
+You may see this error on first use of `update-binfmts`; ignore it and repeat the command and it should succeed.
+```
+update-binfmts: warning: unable to close /proc/sys/fs/binfmt_misc/register: No such file or directory
+update-binfmts: warning: unable to enable binary format rosetta
+update-binfmts: exiting due to previous errors
+```
+
+If you intend to use `docker` in the arm64 Linux guest to run containers with the `linux/amd64` platform, it's a good
+idea to set this environment variable in your MacOS host for the MacOS `docker` client to use as a default:
+
+```shell
+export DOCKER_DEFAULT_PLATFORM=linux/amd64
+```
+
+This environment variable could also be specified in the `/lib/systemd/system/docker.service` systemd unit file on the
+arm64 Linux guest by adding this line to the `[Service]` stanza:
+
+```ini
+Environment=DOCKER_DEFAULT_PLATFORM=linux/amd64
+```
+
+## Original README follows
+
+---
 #  Virtualization.framework tool (vftool)
 
 Here lies a _really minimalist_ and very noddy command-line wrapper to run VMs in the macOS Big Sur Virtualization.framework.

vftool/main.m

@@ -96,7 +96,8 @@ static int createPty(bool waitForConnection)
                                                   NSString *initrd_path,
                                                   struct disc_info *dinfo,
                                                   unsigned int num_discs,
-                                                  NSString *bridged_eth)
+                                                  NSString *bridged_eth,
+                                                  NSString *rosetta_tag)
 {
     /* **************************************************************** */
     /* Linux bootloader setup:
@@ -210,6 +211,27 @@ static int createPty(bool waitForConnection)
 
     [conf setStorageDevices:discs];
 
+    // expose the Rosetta directory share as value of rosetta_tag NSString:
+    if (rosetta_tag) {
+        NSError *validationError;
+        if (![VZVirtioFileSystemDeviceConfiguration validateTag:rosetta_tag error:&validationError]) {
+            // Handle validation error here.
+            NSLog(@"-- Configuration validation failure! %@\n", validationError);
+            return nil;
+        }
+
+        VZLinuxRosettaDirectoryShare *rosettaDirectoryShare = [[VZLinuxRosettaDirectoryShare alloc] initWithError:&validationError];
+        if (validationError) {
+            NSLog(@"-- Configuration validation failure! %@\n", validationError);
+            return nil;
+        }
+
+        VZVirtioFileSystemDeviceConfiguration *fileSystemDevice = [[VZVirtioFileSystemDeviceConfiguration alloc] initWithTag:rosetta_tag];
+        fileSystemDevice.share = rosettaDirectoryShare;
+
+        conf.directorySharingDevices = @[fileSystemDevice];
+    }
+
     return conf;
 }
 
@@ -228,6 +250,7 @@ static void usage(const char *me)
                     "\t-p <number of processors>        (Default 1)\n"
                     "\t-m <memory size in MB>           (Default 512MB)\n"
                     "\t-t <tty type>                    (0 = stdio, 1 = pty (default))\n"
+                    "\t-g <rosetta directory share tag>\n"
                     "\n\tSpecify multiple discs with multiple -d/-c options, in order (max %d)\n",
                     me, MAX_DISCS);
 }
@@ -242,6 +265,7 @@ int main(int argc, char *argv[])
         NSString *disc_path = NULL;
         NSString *cdrom_path = NULL;
         NSString *eth_if = NULL;
+        NSString *rosetta_tag = NULL;
         unsigned int cpus = 0;
         unsigned int mem = 0;
         unsigned int tty_type = 1;
@@ -250,7 +274,7 @@ int main(int argc, char *argv[])
         unsigned int num_discs = 0;
 
         int ch;
-        while ((ch = getopt(argc, argv, "k:a:i:d:c:b:p:m:t:h")) != -1) {
+        while ((ch = getopt(argc, argv, "k:a:i:d:c:b:p:m:t:g:h")) != -1) {
             switch (ch) {
                 case 'k':
                     kern_path = [NSString stringWithUTF8String:optarg];
@@ -289,6 +313,9 @@ int main(int argc, char *argv[])
                         return 1;
                     }
                     break;
+                case 'g':
+                    rosetta_tag = [NSString stringWithUTF8String:optarg];
+                    break;
 
                 case 'h':
                 default:
@@ -323,7 +350,8 @@ int main(int argc, char *argv[])
         VZVirtualMachineConfiguration *conf = getVMConfig(mem, cpus, tty_type, cmdline,
                                                           kern_path, initrd_path,
                                                           dinfo, num_discs,
-                                                          eth_if);
+                                                          eth_if,
+                                                          rosetta_tag);
 
         if (!conf) {
             NSLog(@"Couldn't create configuration for VM.\n");