Switch to using a systemd generator for /var
If one wants to set up a mount for `/var` in `/etc/fstab`, it won't be mounted since `ostree-prepare-root` set up a bind mount for `/var` to `/sysroot/ostree/$stateroot/var`, and systemd will take the already extant mount over what's in `/etc/fstab`. There are a few options to fix this, but what I settled on is parsing `/etc/fstab` in a generator (exactly like `systemd-fstab-generator` does), except here we look for an explicit mount for `/var`, and if one *isn't* found, synthesize the default ostree mount to the stateroot. Another nice property is that if an admin creates a `var.mount` unit in `/etc` for example, that will also override our mount. Note that today ostree doesn't hard depend on systemd, so this behavior only kicks in if we're built with systemd *and* libmount support (for parsing `/etc/fstab`). I didn't really test that case though. Initially I started writing this as a "pure libc" program, but at one point decided to use `libostree.so` to find the booted deployment. That didn't work out because `/boot` wasn't necessarily mounted and hence we couldn't find the bootloader config. A leftover artifact from this is that the generator code calls into libostree via the "cmd private" infrastructure. But it's an easy way to share code, and doesn't hurt. Closes: #859 Approved by: jlebon
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/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
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*
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* Copyright (C) 2017 Colin Walters <walters@verbum.org>
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 02111-1307, USA.
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*/
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#include "config.h"
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#include <glib-unix.h>
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#include <gio/gunixoutputstream.h>
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#include <errno.h>
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#include <stdio.h>
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#ifdef HAVE_LIBMOUNT
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#include <libmount.h>
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#endif
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#include <stdbool.h>
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#include "otutil.h"
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#include "ostree.h"
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#include "ostree-core-private.h"
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#include "ostree-cmdprivate.h"
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#ifdef HAVE_LIBMOUNT
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typedef FILE OtLibMountFile;
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G_DEFINE_AUTOPTR_CLEANUP_FUNC(OtLibMountFile, endmntent);
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/* Taken from systemd path-util.c */
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static bool
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is_path (const char *p)
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{
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return !!strchr (p, '/');
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}
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/* Taken from systemd path-util.c */
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static char*
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path_kill_slashes (char *path)
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{
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char *f, *t;
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bool slash = false;
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/* Removes redundant inner and trailing slashes. Modifies the
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* passed string in-place.
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*
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* For example: ///foo///bar/ becomes /foo/bar
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*/
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for (f = path, t = path; *f; f++)
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{
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if (*f == '/')
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{
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slash = true;
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continue;
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}
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if (slash)
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{
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slash = false;
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*(t++) = '/';
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}
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*(t++) = *f;
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}
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/* Special rule, if we are talking of the root directory, a
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trailing slash is good */
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if (t == path && slash)
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*(t++) = '/';
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*t = 0;
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return path;
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}
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/* Written by ostree-sysroot-deploy.c. We parse out the stateroot here since we
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* need to know it to mount /var. Unfortunately we can't easily use the
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* libostree API to find the booted deployment since /boot might not have been
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* mounted yet.
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*/
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static char *
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stateroot_from_ostree_cmdline (const char *ostree_cmdline,
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GError **error)
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{
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static GRegex *regex;
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static gsize regex_initialized;
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if (g_once_init_enter (®ex_initialized))
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{
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regex = g_regex_new ("^/ostree/boot.[01]/([^/]+)/", 0, 0, NULL);
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g_assert (regex);
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g_once_init_leave (®ex_initialized, 1);
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}
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g_autoptr(GMatchInfo) match = NULL;
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if (!g_regex_match (regex, ostree_cmdline, 0, &match))
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return glnx_null_throw (error, "Failed to parse %s", ostree_cmdline);
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return g_match_info_fetch (match, 1);
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}
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#endif
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/* Implementation of ostree-system-generator */
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gboolean
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_ostree_impl_system_generator (const char *ostree_cmdline,
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const char *normal_dir,
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const char *early_dir,
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const char *late_dir,
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GError **error)
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{
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#ifdef HAVE_LIBMOUNT
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/* Not currently cancellable, but define a var in case we care later */
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GCancellable *cancellable = NULL;
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/* Some path constants to avoid typos */
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static const char fstab_path[] = "/etc/fstab";
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static const char var_path[] = "/var";
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/* ostree-prepare-root was patched to write the stateroot to this file */
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g_autofree char *stateroot = stateroot_from_ostree_cmdline (ostree_cmdline, error);
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if (!stateroot)
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return FALSE;
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/* Load /etc/fstab if it exists, and look for a /var mount */
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g_autoptr(OtLibMountFile) fstab = setmntent (fstab_path, "re");
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gboolean found_var_mnt = FALSE;
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if (!fstab)
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{
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if (errno != ENOENT)
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return glnx_throw_errno_prefix (error, "Reading %s", fstab_path);
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}
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else
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{
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/* Parse it */
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struct mntent *me;
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while ((me = getmntent (fstab)))
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{
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g_autofree char *where = g_strdup (me->mnt_dir);
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if (is_path (where))
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path_kill_slashes (where);
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/* We're only looking for /var here */
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if (strcmp (where, var_path) != 0)
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continue;
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found_var_mnt = TRUE;
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break;
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}
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}
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/* If we found /var, we're done */
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if (found_var_mnt)
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return TRUE;
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/* Prepare to write to the output unit dir; we use the "normal" dir
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* that overrides /usr, but not /etc.
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*/
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glnx_fd_close int normal_dir_dfd = -1;
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if (!glnx_opendirat (AT_FDCWD, normal_dir, TRUE, &normal_dir_dfd, error))
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return FALSE;
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/* Generate our bind mount unit */
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const char *stateroot_var_path = glnx_strjoina ("/sysroot/ostree/deploy/", stateroot, "/var");
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glnx_fd_close int tmpfd = -1;
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g_autofree char *tmppath = NULL;
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if (!glnx_open_tmpfile_linkable_at (normal_dir_dfd, ".", O_WRONLY,
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&tmpfd, &tmppath, error))
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return FALSE;
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g_autoptr(GOutputStream) outstream = g_unix_output_stream_new (tmpfd, FALSE);
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gsize bytes_written;
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/* This code is inspired by systemd's fstab-generator.c.
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*
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* Note that our unit doesn't run if systemd.volatile is enabled;
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* see https://github.com/ostreedev/ostree/pull/856
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*/
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if (!g_output_stream_printf (outstream, &bytes_written, cancellable, error,
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"##\n# Automatically generated by ostree-system-generator\n##\n\n"
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"[Unit]\n"
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"Documentation=man:ostree(1)\n"
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"ConditionKernelCommandLine=!systemd.volatile\n"
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/* We need /sysroot mounted writable first */
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"After=ostree-remount.service\n"
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"Before=local-fs.target\n"
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"\n"
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"[Mount]\n"
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"Where=%s\n"
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"What=%s\n"
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"Options=bind\n",
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var_path,
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stateroot_var_path))
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return FALSE;
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if (!g_output_stream_flush (outstream, cancellable, error))
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return FALSE;
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g_clear_object (&outstream);
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/* It should be readable */
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if (fchmod (tmpfd, 0644) < 0)
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return glnx_throw_errno_prefix (error, "fchmod");
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/* Error out if somehow it already exists, that'll help us debug conflicts */
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if (!glnx_link_tmpfile_at (normal_dir_dfd, GLNX_LINK_TMPFILE_NOREPLACE,
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tmpfd, tmppath, normal_dir_dfd,
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"var.mount", error))
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return FALSE;
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return TRUE;
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#else
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return glnx_throw (error, "Not implemented");
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#endif
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}
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