mkfs-util: Add support to populate vfat without mounting using mcopy

mkfs.vfat doesn't support specifying a root directory to bootstrap
the filesystem from (see dosfstools/dosfstools#183).
Instead, we can use the mcopy tool from the mtools package to copy
files into the vfat filesystem after creating it without needing to
mount the vfat filesystem.

mkosi.conf.d/10-systemd.conf

@@ -21,6 +21,7 @@ Packages=
  coreutils
  diffutils
  dnsmasq
+ dosfstools
  e2fsprogs
  findutils
  gcc # For sanitizer libraries
@@ -30,6 +31,7 @@ Packages=
  kexec-tools
  kmod
  less
+ mtools
  nano
  nftables
  openssl

src/shared/mkfs-util.c

@@ -2,12 +2,15 @@
 
 #include <unistd.h>
 
+#include "dirent-util.h"
+#include "fd-util.h"
 #include "fileio.h"
 #include "id128-util.h"
 #include "mkfs-util.h"
 #include "mountpoint-util.h"
 #include "path-util.h"
 #include "process-util.h"
+#include "stat-util.h"
 #include "stdio-util.h"
 #include "string-util.h"
 #include "utf8.h"
@@ -35,7 +38,7 @@ int mkfs_exists(const char *fstype) {
 }
 
 int mkfs_supports_root_option(const char *fstype) {
- return fstype_is_ro(fstype) || STR_IN_SET(fstype, "ext2", "ext3", "ext4", "btrfs");
+ return fstype_is_ro(fstype) || STR_IN_SET(fstype, "ext2", "ext3", "ext4", "btrfs", "vfat");
 }
 
 static int mangle_linux_fs_label(const char *s, size_t max_len, char **ret) {
@@ -121,6 +124,65 @@ static int setup_userns(uid_t uid, gid_t gid) {
  return 0;
 }
 
+static int do_mcopy(const char *node, const char *root) {
+ _cleanup_strv_free_ char **argv = NULL;
+ _cleanup_closedir_ DIR *rootdir = NULL;
+ struct stat st;
+ int r;
+
+ assert(node);
+ assert(root);
+
+ /* Return early if there's nothing to copy. */
+ if (dir_is_empty(root, /*ignore_hidden_or_backup=*/ false))
+ return 0;
+
+ argv = strv_new("mcopy", "-b", "-s", "-p", "-Q", "-n", "-m", "-i", node);
+ if (!argv)
+ return log_oom();
+
+ /* mcopy copies the top level directory instead of everything in it so we have to pass all
+ * the subdirectories to mcopy instead to end up with the correct directory structure. */
+
+ rootdir = opendir(root);
+ if (!rootdir)
+ return log_error_errno(errno, "Failed to open directory '%s'", root);
+
+ FOREACH_DIRENT(de, rootdir, return -errno) {
+ char *p = path_join(root, de->d_name);
+ if (!p)
+ return log_oom();
+
+ r = strv_consume(&argv, TAKE_PTR(p));
+ if (r < 0)
+ return log_oom();
+ }
+
+ r = strv_extend(&argv, "::");
+ if (r < 0)
+ return log_oom();
+
+ if (stat(root, &st) < 0)
+ return log_error_errno(errno, "Failed to stat %s: %m", root);
+
+ r = safe_fork("(mcopy)", FORK_RESET_SIGNALS|FORK_RLIMIT_NOFILE_SAFE|FORK_DEATHSIG|FORK_LOG|FORK_WAIT|FORK_STDOUT_TO_STDERR|FORK_NEW_USERNS, NULL);
+ if (r < 0)
+ return r;
+ if (r == 0) {
+ r = setup_userns(st.st_uid, st.st_gid);
+ if (r < 0)
+ _exit(EXIT_FAILURE);
+
+ execvp("mcopy", argv);
+
+ log_error_errno(errno, "Failed to execute mcopy: %m");
+
+ _exit(EXIT_FAILURE);
+ }
+
+ return 0;
+}
+
 int make_filesystem(
  const char *node,
  const char *fstype,
@@ -344,6 +406,12 @@ int make_filesystem(
  _exit(EXIT_FAILURE);
  }
 
+ if (root && streq(fstype, "vfat")) {
+ r = do_mcopy(node, root);
+ if (r < 0)
+ return r;
+ }
+
  if (STR_IN_SET(fstype, "ext2", "ext3", "ext4", "btrfs", "f2fs", "xfs", "vfat", "swap"))
  log_info("%s successfully formatted as %s (label \"%s\", uuid %s)",
  node, fstype, label, vol_id);

test/TEST-58-REPART/test.sh

@@ -13,6 +13,7 @@ test_append_files() {
  if command -v openssl >/dev/null 2>&1; then
  inst_binary openssl
  fi
+ inst_binary mcopy
  instmods dm_verity =md
  generate_module_dependencies
  fi