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prepare-var: Do not remount stateroot var in-place, and unmount the temporary var mount after real /var is mounted #3363

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prepare-var: Do not remount stateroot var in-place, and unmount the temporary var mount after real /var is mounted #3363

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48f5ced
prepare-root: Bind var under /run instead of inplace
ruihe774 Dec 18, 2024
d25cd57
prepare-root: Unmount temporary var mount after /var is mounted
ruihe774 Dec 19, 2024
d472e60
prepare-root: It's not necessary to make /var slave anymore
ruihe774 Dec 20, 2024
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156 changes: 66 additions & 90 deletions src/libostree/ostree-impl-system-generator.c
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Original file line number Diff line number Diff line change
Expand Up @@ -126,31 +126,32 @@ require_internal_units (const char *normal_dir, const char *early_dir, const cha
#endif
}

// Resolve symlink to return osname
static gboolean
_ostree_sysroot_parse_bootlink_aboot (const char *bootlink, char **out_osname, GError **error)
write_unit_file (int dir_fd, const char *path, GCancellable *cancellable, GError **error, const char *fmt, ...)
{
static gsize regex_initialized;
static GRegex *regex;
g_autofree char *symlink_val = glnx_readlinkat_malloc (-1, bootlink, NULL, error);
if (!symlink_val)
return glnx_prefix_error (error, "Failed to read '%s' symlink", bootlink);

if (g_once_init_enter (&regex_initialized))
{
regex = g_regex_new ("^deploy/([^/]+)/", 0, 0, NULL);
g_assert (regex);
g_once_init_leave (&regex_initialized, 1);
}

g_autoptr (GMatchInfo) match = NULL;
if (!g_regex_match (regex, symlink_val, 0, &match))
return glnx_throw (error,
"Invalid aboot symlink in /ostree, expected symlink to resolve to "
"deploy/OSNAME/... instead it resolves to '%s'",
symlink_val);

*out_osname = g_match_info_fetch (match, 1);
g_auto (GLnxTmpfile) tmpf = {
0,
};
if (!glnx_open_tmpfile_linkable_at (dir_fd, ".", O_WRONLY | O_CLOEXEC, &tmpf, error))
return FALSE;
g_autoptr (GOutputStream) outstream = g_unix_output_stream_new (tmpf.fd, FALSE);
gsize bytes_written;
va_list args;
va_start (args, fmt);
const gboolean r = g_output_stream_vprintf (outstream, &bytes_written, cancellable, error, fmt, args);
va_end (args);
if (!r)
return FALSE;
if (!g_output_stream_flush (outstream, cancellable, error))
return FALSE;
g_clear_object (&outstream);
/* It should be readable */
if (!glnx_fchmod (tmpf.fd, 0644, error))
return FALSE;
/* Error out if somehow it already exists, that'll help us debug conflicts */
if (!glnx_link_tmpfile_at (&tmpf, GLNX_LINK_TMPFILE_NOREPLACE, dir_fd, path,
error))
return FALSE;
return TRUE;
}

Expand All @@ -163,22 +164,37 @@ fstab_generator (const char *ostree_target, const bool is_aboot, const char *nor
/* Not currently cancellable, but define a var in case we care later */
GCancellable *cancellable = NULL;
/* Some path constants to avoid typos */
static const char fstab_path[] = "/etc/fstab";
static const char var_path[] = "/var";
const char *fstab_path = "/etc/fstab";
const char *var_dst = "/var";
const char *var_src = OTCORE_RUN_OSTREE_PRIVATE "/var";

/* Written by ostree-sysroot-deploy.c. We parse out the stateroot here since we
* need to know it to mount /var. Unfortunately we can't easily use the
* libostree API to find the booted deployment since /boot might not have been
* mounted yet.
/* Prepare to write to the output unit dir; we use the "normal" dir
* that overrides /usr, but not /etc.
*/
g_autofree char *stateroot = NULL;
if (is_aboot)
{
if (!_ostree_sysroot_parse_bootlink_aboot (ostree_target, &stateroot, error))
return glnx_prefix_error (error, "Parsing aboot stateroot");
}
else if (!_ostree_sysroot_parse_bootlink (ostree_target, NULL, &stateroot, NULL, NULL, error))
return glnx_prefix_error (error, "Parsing stateroot");
glnx_autofd int normal_dir_dfd = -1;
if (!glnx_opendirat (AT_FDCWD, normal_dir, TRUE, &normal_dir_dfd, error))
return FALSE;

/* Generate a unit to unmount var_src */
if (!write_unit_file (normal_dir_dfd, "ostree-unmount-temp-var.service", cancellable, error,
"##\n# Automatically generated by ostree-system-generator\n##\n\n"
"[Unit]\n"
"Documentation=man:ostree(1)\n"
"ConditionPathIsMountPoint=%s\n"
"After=var.mount\n"
"\n"
"[Service]\n"
"Type=oneshot\n"
"ExecStart=/usr/bin/umount --lazy %s\n",
var_src, var_src))
return FALSE;

if (!glnx_shutil_mkdir_p_at (normal_dir_dfd, "local-fs.target.wants", 0755, cancellable,
error))
return FALSE;
if (symlinkat ("../ostree-unmount-temp-var.service", normal_dir_dfd,
"local-fs.target.wants/ostree-unmount-temp-var.service") < 0)
return glnx_throw_errno_prefix (error, "symlinkat");

/* Load /etc/fstab if it exists, and look for a /var mount */
g_autoptr (OtLibMountFile) fstab = setmntent (fstab_path, "re");
Expand All @@ -199,7 +215,7 @@ fstab_generator (const char *ostree_target, const bool is_aboot, const char *nor
path_kill_slashes (where);

/* We're only looking for /var here */
if (strcmp (where, var_path) != 0)
if (strcmp (where, var_dst) != 0)
continue;

found_var_mnt = TRUE;
Expand All @@ -211,59 +227,19 @@ fstab_generator (const char *ostree_target, const bool is_aboot, const char *nor
if (found_var_mnt)
return TRUE;

/* Prepare to write to the output unit dir; we use the "normal" dir
* that overrides /usr, but not /etc.
*/
glnx_autofd int normal_dir_dfd = -1;
if (!glnx_opendirat (AT_FDCWD, normal_dir, TRUE, &normal_dir_dfd, error))
return FALSE;

/* Generate our bind mount unit */
const char *stateroot_var_path = glnx_strjoina ("/sysroot/ostree/deploy/", stateroot, "/var");

g_auto (GLnxTmpfile) tmpf = {
0,
};
if (!glnx_open_tmpfile_linkable_at (normal_dir_dfd, ".", O_WRONLY | O_CLOEXEC, &tmpf, error))
return FALSE;
g_autoptr (GOutputStream) outstream = g_unix_output_stream_new (tmpf.fd, FALSE);
gsize bytes_written;
/* This code is inspired by systemd's fstab-generator.c.
*
* Note that our unit doesn't run if systemd.volatile is enabled;
* see https://github.com/ostreedev/ostree/pull/856
*
* To avoid having submounts of /var propagate into $stateroot/var, the mount
* is made with slave+shared propagation. This means that /var will receive
* mount events from the parent /sysroot mount, but not vice versa. Adding a
* shared peer group below the slave group means that submounts of /var will
* inherit normal shared propagation. See mount_namespaces(7), Linux
* Documentation/filesystems/sharedsubtree.txt and
* https://github.com/ostreedev/ostree/issues/2086. This also happens in
* ostree-prepare-root.c for the INITRAMFS_MOUNT_VAR case.
*/
if (!g_output_stream_printf (outstream, &bytes_written, cancellable, error,
"##\n# Automatically generated by ostree-system-generator\n##\n\n"
"[Unit]\n"
"Documentation=man:ostree(1)\n"
"ConditionKernelCommandLine=!systemd.volatile\n"
"Before=local-fs.target\n"
"\n"
"[Mount]\n"
"Where=%s\n"
"What=%s\n"
"Options=bind,slave,shared\n",
var_path, stateroot_var_path))
return FALSE;
if (!g_output_stream_flush (outstream, cancellable, error))
return FALSE;
g_clear_object (&outstream);
/* It should be readable */
if (!glnx_fchmod (tmpf.fd, 0644, error))
return FALSE;
/* Error out if somehow it already exists, that'll help us debug conflicts */
if (!glnx_link_tmpfile_at (&tmpf, GLNX_LINK_TMPFILE_NOREPLACE, normal_dir_dfd, "var.mount",
error))
if (!write_unit_file (normal_dir_dfd, "var.mount", cancellable, error,
"##\n# Automatically generated by ostree-system-generator\n##\n\n"
"[Unit]\n"
"Documentation=man:ostree(1)\n"
"ConditionKernelCommandLine=!systemd.volatile\n"
"Before=local-fs.target\n"
"\n"
"[Mount]\n"
"Where=%s\n"
"What=%s\n"
"Options=bind\n",
var_dst, var_src))
return FALSE;

/* And ensure it's required; newer systemd will auto-inject fs dependencies
Expand Down
54 changes: 21 additions & 33 deletions src/switchroot/ostree-prepare-root.c
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Original file line number Diff line number Diff line change
Expand Up @@ -389,19 +389,16 @@ main (int argc, char *argv[])

g_autofree char *expected_digest = NULL;

// For now we just stick the transient root on the default /run tmpfs;
// however, see
// https://github.com/systemd/systemd/blob/604b2001081adcbd64ee1fbe7de7a6d77c5209fe/src/basic/mountpoint-util.h#L36
// which bumps up these defaults for the rootfs a bit.
g_autofree char *root_upperdir
= root_transient ? g_build_filename (OTCORE_RUN_OSTREE_PRIVATE, "root/upper", NULL)
: NULL;
g_autofree char *root_workdir
= root_transient ? g_build_filename (OTCORE_RUN_OSTREE_PRIVATE, "root/work", NULL) : NULL;

// Propagate these options for transient root, if provided
if (root_transient)
{
// For now we just stick the transient root on the default /run tmpfs;
// however, see
// https://github.com/systemd/systemd/blob/604b2001081adcbd64ee1fbe7de7a6d77c5209fe/src/basic/mountpoint-util.h#L36
// which bumps up these defaults for the rootfs a bit.
const char *root_upperdir = OTCORE_RUN_OSTREE_PRIVATE "/root/upper";
const char *root_workdir = OTCORE_RUN_OSTREE_PRIVATE "/root/work";

if (!glnx_shutil_mkdir_p_at (AT_FDCWD, root_upperdir, 0755, NULL, &error))
errx (EXIT_FAILURE, "Failed to create %s: %s", root_upperdir, error->message);
if (!glnx_shutil_mkdir_p_at (AT_FDCWD, root_workdir, 0700, NULL, &error))
Expand Down Expand Up @@ -611,17 +608,15 @@ main (int argc, char *argv[])
err (EXIT_FAILURE, "failed to bind mount (class:readonly) /usr");
}

/* Prepare /var.
* When a read-only sysroot is configured, this adds a dedicated bind-mount (to itself)
* so that the stateroot location stays writable. */
if (sysroot_readonly)
{
/* Bind-mount /var (at stateroot path), and remount as writable. */
if (mount ("../../var", "../../var", NULL, MS_BIND | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to prepare /var bind-mount at %s", srcpath);
if (mount ("../../var", "../../var", NULL, MS_BIND | MS_REMOUNT | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to make writable /var bind-mount at %s", srcpath);
}
const char *var_dir = OTCORE_RUN_OSTREE_PRIVATE "/var";

/* Bind-mount /var, and remount as writable. */
if (mkdirat (AT_FDCWD, var_dir, 0) < 0)
err (EXIT_FAILURE, "failed to mkdir %s", var_dir);
if (mount ("../../var", var_dir, NULL, MS_BIND | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to prepare /var bind-mount at %s", var_dir);
if (mount (var_dir, var_dir, NULL, MS_BIND | MS_REMOUNT | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to make writable /var bind-mount at %s", var_dir);

/* When running under systemd, /var will be handled by a 'var.mount' unit outside
* of initramfs.
Expand All @@ -640,18 +635,11 @@ main (int argc, char *argv[])
*/
if (mount_var)
{
if (mount ("../../var", TMP_SYSROOT "/var", NULL, MS_BIND | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to bind mount ../../var to var");

/* To avoid having submounts of /var propagate into $stateroot/var, the
* mount is made with slave+shared propagation. See the comment in
* ostree-impl-system-generator.c when /var isn't mounted in the
* initramfs for further explanation.
*/
if (mount (NULL, TMP_SYSROOT "/var", NULL, MS_SLAVE | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to change /var to slave mount");
if (mount (NULL, TMP_SYSROOT "/var", NULL, MS_SHARED | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to change /var to slave+shared mount");
if (mount (var_dir, TMP_SYSROOT "/var", NULL, MS_BIND | MS_SILENT, NULL) < 0)
err (EXIT_FAILURE, "failed to bind mount %s to /var", var_dir);

if (umount2 (var_dir, MNT_DETACH) < 0)
err (EXIT_FAILURE, "failed to umount %s", var_dir);
}

/* This can be used by other things to signal ostree is in use */
Expand Down
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