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In the OSTree model, executables go in `/usr`, state in `/var` and configuration in `/etc`. Software that lives in `/opt` however messes this up because it often mixes code *and* state, making it harder to manage. More generally, it's sometimes useful to have the OSTree commit contain code under a certain path, but still allow that path to be writable by software and the sysadmin at runtime (`/usr/local` is another instance). Add the concept of state overlays. A state overlay is an overlayfs mount whose upper directory, which contains unmanaged state, is carried forward on top of a lower directory, containing OSTree-managed files. In the example of `/usr/local`, OSTree commits can ship content there, all while allowing users to e.g. add scripts in `/usr/local/bin` when booted into that commit. Some reconciliation logic is executed whenever the base is updated so that newer files in the base are never shadowed by a copied up version in the upper directory. This matches RPM semantics when upgrading packages whose files may have been modified. For ease of integration, this is exposed as a systemd template unit which any downstream distro/user can enable. The instance name is the mountpath in escaped systemd path notation (e.g. `ostree-state-overlay@usr-local.service`). See discussions in #3113 for more details.
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# Copyright (C) 2023 Red Hat Inc. | ||
# | ||
# This library is free software; you can redistribute it and/or | ||
# modify it under the terms of the GNU Lesser General Public | ||
# License as published by the Free Software Foundation; either | ||
# version 2 of the License, or (at your option) any later version. | ||
# | ||
# This library is distributed in the hope that it will be useful, | ||
# but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
# Lesser General Public License for more details. | ||
# | ||
# You should have received a copy of the GNU Lesser General Public | ||
# License along with this library. If not, see <https://www.gnu.org/licenses/>. | ||
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[Unit] | ||
Description=OSTree State Overlay On /%I | ||
Documentation=man:ostree(1) | ||
DefaultDependencies=no | ||
ConditionKernelCommandLine=ostree | ||
# run after /var is setup since that's where the upperdir is stored | ||
# and after boot.mount so we can load the sysroot | ||
After=var.mount boot.mount | ||
# but before local-fs.target, which we consider ourselves a part of | ||
Before=local-fs.target | ||
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[Service] | ||
Type=oneshot | ||
RemainAfterExit=yes | ||
ExecStart=/usr/bin/ostree admin state-overlay %i /%I | ||
StandardInput=null | ||
StandardOutput=journal | ||
StandardError=journal+console | ||
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[Install] | ||
WantedBy=local-fs.target |
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/* Copyright (C) 2023 Red Hat, Inc. | ||
* | ||
* SPDX-License-Identifier: LGPL-2.0+ | ||
* | ||
* This library is free software; you can redistribute it and/or | ||
* modify it under the terms of the GNU Lesser General Public | ||
* License as published by the Free Software Foundation; either | ||
* version 2 of the License, or (at your option) any later version. | ||
* | ||
* This library is distributed in the hope that it will be useful, | ||
* but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
* Lesser General Public License for more details. | ||
* | ||
* You should have received a copy of the GNU Lesser General Public | ||
* License along with this library. If not, see <https://www.gnu.org/licenses/>. | ||
*/ | ||
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#include "config.h" | ||
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#include <fcntl.h> | ||
#include <glib-unix.h> | ||
#include <sched.h> | ||
#include <stdlib.h> | ||
#include <sys/mount.h> | ||
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#include "glnx-errors.h" | ||
#include "glnx-fdio.h" | ||
#include "glnx-local-alloc.h" | ||
#include "glnx-shutil.h" | ||
#include "glnx-xattrs.h" | ||
#include "ostree-core.h" | ||
#include "ostree-deployment.h" | ||
#include "ot-admin-builtins.h" | ||
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#define OSTREE_STATEOVERLAYS_DIR "/var/ostree/state-overlays" | ||
#define OSTREE_STATEOVERLAY_UPPER_DIR "upper" | ||
#define OSTREE_STATEOVERLAY_WORK_DIR "work" | ||
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#define OSTREE_STATEOVERLAY_XATTR_DEPLOYMENT_CSUM "user.ostree.deploymentcsum" | ||
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/* https://www.kernel.org/doc/html/latest/filesystems/overlayfs.html */ | ||
#define OVERLAYFS_DIR_XATTR_OPAQUE "trusted.overlay.opaque" | ||
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static GOptionEntry options[] = { { NULL } }; | ||
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static gboolean | ||
ensure_overlay_dirs (const char *overlay_dir, int *out_overlay_dfd, GCancellable *cancellable, | ||
GError **error) | ||
{ | ||
glnx_autofd int overlay_dfd = -1; | ||
if (!glnx_shutil_mkdir_p_at_open (AT_FDCWD, overlay_dir, 0700, &overlay_dfd, cancellable, error)) | ||
return FALSE; | ||
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if (!glnx_shutil_mkdir_p_at (overlay_dfd, OSTREE_STATEOVERLAY_WORK_DIR, 0700, cancellable, error)) | ||
return FALSE; | ||
if (!glnx_shutil_mkdir_p_at (overlay_dfd, OSTREE_STATEOVERLAY_UPPER_DIR, 0700, cancellable, | ||
error)) | ||
return FALSE; | ||
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*out_overlay_dfd = glnx_steal_fd (&overlay_dfd); | ||
return TRUE; | ||
} | ||
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/* XXX: upstream to libglnx */ | ||
static gboolean | ||
lgetxattrat_allow_noent (int dfd, const char *path, const char *attribute, GBytes **out_bytes, | ||
GError **error) | ||
{ | ||
g_autoptr (GError) local_error = NULL; | ||
*out_bytes = glnx_lgetxattrat (dfd, path, attribute, &local_error); | ||
if (!*out_bytes) | ||
{ | ||
if (g_error_matches (local_error, G_IO_ERROR, G_IO_ERROR_INVALID_DATA)) | ||
return TRUE; | ||
g_propagate_error (error, g_steal_pointer (&local_error)); | ||
return FALSE; | ||
} | ||
return TRUE; | ||
} | ||
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static gboolean | ||
is_opaque_dir (int dfd, const char *dname, gboolean *out_is_opaque, GError **error) | ||
{ | ||
g_autoptr (GBytes) data = NULL; | ||
if (!lgetxattrat_allow_noent (dfd, dname, OVERLAYFS_DIR_XATTR_OPAQUE, &data, error)) | ||
return FALSE; | ||
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if (!data) | ||
*out_is_opaque = FALSE; | ||
else | ||
{ | ||
gsize size; | ||
const guint8 *buf = g_bytes_get_data (data, &size); | ||
*out_is_opaque = (size == 1 && buf[0] == 'y'); | ||
} | ||
return TRUE; | ||
} | ||
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static gboolean | ||
prune_upperdir_recurse (int lower_dfd, int upper_dfd, GCancellable *cancellable, GError **error) | ||
{ | ||
g_auto (GLnxDirFdIterator) dfd_iter = { 0 }; | ||
if (!glnx_dirfd_iterator_init_at (upper_dfd, ".", FALSE, &dfd_iter, error)) | ||
return FALSE; | ||
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while (TRUE) | ||
{ | ||
struct dirent *dent = NULL; | ||
if (!glnx_dirfd_iterator_next_dent_ensure_dtype (&dfd_iter, &dent, cancellable, error)) | ||
return FALSE; | ||
if (dent == NULL) | ||
break; | ||
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/* do we have an entry of the same name in the lowerdir? */ | ||
struct stat stbuf; | ||
if (!glnx_fstatat_allow_noent (lower_dfd, dent->d_name, &stbuf, AT_SYMLINK_NOFOLLOW, error)) | ||
return FALSE; | ||
if (errno == ENOENT) | ||
continue; /* state file (i.e. upperdir only); carry on */ | ||
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/* ok, it shadows; are they both directories? */ | ||
if (dent->d_type == DT_DIR && S_ISDIR (stbuf.st_mode)) | ||
{ | ||
/* is the directory opaque? */ | ||
gboolean is_opaque = FALSE; | ||
if (!is_opaque_dir (upper_dfd, dent->d_name, &is_opaque, error)) | ||
return FALSE; | ||
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if (!is_opaque) | ||
{ | ||
/* recurse */ | ||
glnx_autofd int lower_subdfd = -1; | ||
if (!glnx_opendirat (lower_dfd, dent->d_name, FALSE, &lower_subdfd, error)) | ||
return FALSE; | ||
glnx_autofd int upper_subdfd = -1; | ||
if (!glnx_opendirat (upper_dfd, dent->d_name, FALSE, &upper_subdfd, error)) | ||
return FALSE; | ||
if (!prune_upperdir_recurse (lower_subdfd, upper_subdfd, cancellable, error)) | ||
return glnx_prefix_error (error, "in %s", dent->d_name); | ||
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continue; | ||
} | ||
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/* fallthrough; implicitly delete opaque directories */ | ||
} | ||
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/* any other case, we prune (this also implicitly covers whiteouts and opaque dirs) */ | ||
if (dent->d_type == DT_DIR) | ||
{ | ||
if (!glnx_shutil_rm_rf_at (upper_dfd, dent->d_name, cancellable, error)) | ||
return FALSE; | ||
} | ||
else | ||
{ | ||
/* just unlinkat(); saves one openat() call */ | ||
if (!glnx_unlinkat (upper_dfd, dent->d_name, 0, error)) | ||
return FALSE; | ||
} | ||
} | ||
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return TRUE; | ||
} | ||
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static gboolean | ||
prune_upperdir (int sysroot_fd, const char *mountpath, int overlay_dfd, GCancellable *cancellable, | ||
GError **error) | ||
{ | ||
glnx_autofd int lower_dfd = -1; | ||
if (!glnx_opendirat (AT_FDCWD, mountpath, FALSE, &lower_dfd, error)) | ||
return FALSE; | ||
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glnx_autofd int upper_dfd = -1; | ||
if (!glnx_opendirat (overlay_dfd, OSTREE_STATEOVERLAY_UPPER_DIR, FALSE, &upper_dfd, error)) | ||
return FALSE; | ||
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if (!prune_upperdir_recurse (lower_dfd, upper_dfd, cancellable, error)) | ||
return FALSE; | ||
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return TRUE; | ||
} | ||
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static gboolean | ||
mount_overlay (const char *mountpath, const char *name, GError **error) | ||
{ | ||
/* we could use /proc/self/... with overlay_dfd to avoid these allocations, | ||
* but this gets stringified into the options field in the mount table, and | ||
* being cryptic is not helpful */ | ||
g_autofree char *upperdir | ||
= g_build_filename (OSTREE_STATEOVERLAYS_DIR, name, OSTREE_STATEOVERLAY_UPPER_DIR, NULL); | ||
g_autofree char *workdir | ||
= g_build_filename (OSTREE_STATEOVERLAYS_DIR, name, OSTREE_STATEOVERLAY_WORK_DIR, NULL); | ||
g_autofree char *ovl_options | ||
= g_strdup_printf ("lowerdir=%s,upperdir=%s,workdir=%s", mountpath, upperdir, workdir); | ||
if (mount ("overlay", mountpath, "overlay", MS_SILENT, ovl_options) < 0) | ||
return glnx_throw_errno_prefix (error, "mount(%s)", mountpath); | ||
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return TRUE; | ||
} | ||
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static gboolean | ||
get_overlay_deployment_checksum (int overlay_dfd, char **out_checksum, GCancellable *cancellable, | ||
GError **error) | ||
{ | ||
g_autoptr (GBytes) bytes = NULL; | ||
if (!lgetxattrat_allow_noent (overlay_dfd, OSTREE_STATEOVERLAY_UPPER_DIR, | ||
OSTREE_STATEOVERLAY_XATTR_DEPLOYMENT_CSUM, &bytes, error)) | ||
return FALSE; | ||
if (!bytes) | ||
return TRUE; /* probably newly created */ | ||
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gsize len; | ||
const char *data = g_bytes_get_data (bytes, &len); | ||
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if (len != OSTREE_SHA256_STRING_LEN) | ||
return TRUE; /* invalid; gracefully handle as missing */ | ||
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*out_checksum = g_strndup (data, len); | ||
return TRUE; | ||
} | ||
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static gboolean | ||
set_overlay_deployment_checksum (int overlay_dfd, const char *checksum, GCancellable *cancellable, | ||
GError **error) | ||
{ | ||
g_assert_cmpuint (strlen (checksum), ==, OSTREE_SHA256_STRING_LEN); | ||
/* we could store it in binary of course, but let's make it more accessible for debugging */ | ||
if (!glnx_lsetxattrat (overlay_dfd, OSTREE_STATEOVERLAY_UPPER_DIR, | ||
OSTREE_STATEOVERLAY_XATTR_DEPLOYMENT_CSUM, (guint8 *)checksum, | ||
OSTREE_SHA256_STRING_LEN, 0, error)) | ||
return FALSE; | ||
return TRUE; | ||
} | ||
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/* Called by ostree-state-overlay@.service. */ | ||
gboolean | ||
ot_admin_builtin_state_overlay (int argc, char **argv, OstreeCommandInvocation *invocation, | ||
GCancellable *cancellable, GError **error) | ||
{ | ||
g_autoptr (GOptionContext) context = g_option_context_new ("NAME MOUNTPATH"); | ||
g_autoptr (OstreeSysroot) sysroot = NULL; | ||
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/* First parse the args without loading the sysroot to see what options are | ||
* set. */ | ||
if (!ostree_admin_option_context_parse (context, options, &argc, &argv, | ||
OSTREE_ADMIN_BUILTIN_FLAG_NONE, invocation, &sysroot, | ||
cancellable, error)) | ||
return FALSE; | ||
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if (argc < 3) | ||
return glnx_throw (error, "Missing NAME or MOUNTPATH"); | ||
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/* Sanity-check */ | ||
OstreeDeployment *booted_deployment = ostree_sysroot_get_booted_deployment (sysroot); | ||
if (booted_deployment == NULL) | ||
return glnx_throw (error, "Must be booted into an OSTree deployment"); | ||
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const char *overlay_name = argv[1]; | ||
const char *mountpath = argv[2]; | ||
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glnx_autofd int overlay_dfd = -1; | ||
g_autofree char *overlay_dir = g_build_filename (OSTREE_STATEOVERLAYS_DIR, overlay_name, NULL); | ||
if (!ensure_overlay_dirs (overlay_dir, &overlay_dfd, cancellable, error)) | ||
return FALSE; | ||
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g_autofree char *current_checksum = NULL; | ||
if (!get_overlay_deployment_checksum (overlay_dfd, ¤t_checksum, cancellable, error)) | ||
return FALSE; | ||
/* note current_checksum could still be NULL */ | ||
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const char *target_checksum = ostree_deployment_get_csum (booted_deployment); | ||
if (g_strcmp0 (current_checksum, target_checksum) != 0) | ||
{ | ||
/* the lowerdir was updated; prune the upperdir */ | ||
if (!prune_upperdir (ostree_sysroot_get_fd (sysroot), mountpath, overlay_dfd, cancellable, | ||
error)) | ||
return glnx_prefix_error (error, "Pruning upperdir for %s", overlay_name); | ||
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if (!set_overlay_deployment_checksum (overlay_dfd, target_checksum, cancellable, error)) | ||
return FALSE; | ||
} | ||
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return mount_overlay (mountpath, overlay_name, error); | ||
} |
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