util-lib: move mount related utility calls to mount-util.[ch]

1 files changed, 483 insertions, 0 deletions

diff --git a/src/basic/mount-util.c b/src/basic/mount-util.c
new file mode 100644
index 0000000000..6b33d43024
--- /dev/null
+++ b/src/basic/mount-util.c
@@ -0,0 +1,483 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2010 Lennart Poettering
+
+  systemd 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 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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 systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/statvfs.h>
+
+#include "escape.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "mount-util.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "set.h"
+#include "string-util.h"
+#include "util.h"
+
+static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id) {
+        char path[strlen("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)];
+        _cleanup_free_ char *fdinfo = NULL;
+        _cleanup_close_ int subfd = -1;
+        char *p;
+        int r;
+
+        if ((flags & AT_EMPTY_PATH) && isempty(filename))
+                xsprintf(path, "/proc/self/fdinfo/%i", fd);
+        else {
+                subfd = openat(fd, filename, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_PATH);
+                if (subfd < 0)
+                        return -errno;
+
+                xsprintf(path, "/proc/self/fdinfo/%i", subfd);
+        }
+
+        r = read_full_file(path, &fdinfo, NULL);
+        if (r == -ENOENT) /* The fdinfo directory is a relatively new addition */
+                return -EOPNOTSUPP;
+        if (r < 0)
+                return -errno;
+
+        p = startswith(fdinfo, "mnt_id:");
+        if (!p) {
+                p = strstr(fdinfo, "\nmnt_id:");
+                if (!p) /* The mnt_id field is a relatively new addition */
+                        return -EOPNOTSUPP;
+
+                p += 8;
+        }
+
+        p += strspn(p, WHITESPACE);
+        p[strcspn(p, WHITESPACE)] = 0;
+
+        return safe_atoi(p, mnt_id);
+}
+
+
+int fd_is_mount_point(int fd, const char *filename, int flags) {
+        union file_handle_union h = FILE_HANDLE_INIT, h_parent = FILE_HANDLE_INIT;
+        int mount_id = -1, mount_id_parent = -1;
+        bool nosupp = false, check_st_dev = true;
+        struct stat a, b;
+        int r;
+
+        assert(fd >= 0);
+        assert(filename);
+
+        /* First we will try the name_to_handle_at() syscall, which
+         * tells us the mount id and an opaque file "handle". It is
+         * not supported everywhere though (kernel compile-time
+         * option, not all file systems are hooked up). If it works
+         * the mount id is usually good enough to tell us whether
+         * something is a mount point.
+         *
+         * If that didn't work we will try to read the mount id from
+         * /proc/self/fdinfo/<fd>. This is almost as good as
+         * name_to_handle_at(), however, does not return the
+         * opaque file handle. The opaque file handle is pretty useful
+         * to detect the root directory, which we should always
+         * consider a mount point. Hence we use this only as
+         * fallback. Exporting the mnt_id in fdinfo is a pretty recent
+         * kernel addition.
+         *
+         * As last fallback we do traditional fstat() based st_dev
+         * comparisons. This is how things were traditionally done,
+         * but unionfs breaks breaks this since it exposes file
+         * systems with a variety of st_dev reported. Also, btrfs
+         * subvolumes have different st_dev, even though they aren't
+         * real mounts of their own. */
+
+        r = name_to_handle_at(fd, filename, &h.handle, &mount_id, flags);
+        if (r < 0) {
+                if (errno == ENOSYS)
+                        /* This kernel does not support name_to_handle_at()
+                         * fall back to simpler logic. */
+                        goto fallback_fdinfo;
+                else if (errno == EOPNOTSUPP)
+                        /* This kernel or file system does not support
+                         * name_to_handle_at(), hence let's see if the
+                         * upper fs supports it (in which case it is a
+                         * mount point), otherwise fallback to the
+                         * traditional stat() logic */
+                        nosupp = true;
+                else
+                        return -errno;
+        }
+
+        r = name_to_handle_at(fd, "", &h_parent.handle, &mount_id_parent, AT_EMPTY_PATH);
+        if (r < 0) {
+                if (errno == EOPNOTSUPP) {
+                        if (nosupp)
+                                /* Neither parent nor child do name_to_handle_at()?
+                                   We have no choice but to fall back. */
+                                goto fallback_fdinfo;
+                        else
+                                /* The parent can't do name_to_handle_at() but the
+                                 * directory we are interested in can?
+                                 * If so, it must be a mount point. */
+                                return 1;
+                } else
+                        return -errno;
+        }
+
+        /* The parent can do name_to_handle_at() but the
+         * directory we are interested in can't? If so, it
+         * must be a mount point. */
+        if (nosupp)
+                return 1;
+
+        /* If the file handle for the directory we are
+         * interested in and its parent are identical, we
+         * assume this is the root directory, which is a mount
+         * point. */
+
+        if (h.handle.handle_bytes == h_parent.handle.handle_bytes &&
+            h.handle.handle_type == h_parent.handle.handle_type &&
+            memcmp(h.handle.f_handle, h_parent.handle.f_handle, h.handle.handle_bytes) == 0)
+                return 1;
+
+        return mount_id != mount_id_parent;
+
+fallback_fdinfo:
+        r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id);
+        if (r == -EOPNOTSUPP)
+                goto fallback_fstat;
+        if (r < 0)
+                return r;
+
+        r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id_parent);
+        if (r < 0)
+                return r;
+
+        if (mount_id != mount_id_parent)
+                return 1;
+
+        /* Hmm, so, the mount ids are the same. This leaves one
+         * special case though for the root file system. For that,
+         * let's see if the parent directory has the same inode as we
+         * are interested in. Hence, let's also do fstat() checks now,
+         * too, but avoid the st_dev comparisons, since they aren't
+         * that useful on unionfs mounts. */
+        check_st_dev = false;
+
+fallback_fstat:
+        /* yay for fstatat() taking a different set of flags than the other
+         * _at() above */
+        if (flags & AT_SYMLINK_FOLLOW)
+                flags &= ~AT_SYMLINK_FOLLOW;
+        else
+                flags |= AT_SYMLINK_NOFOLLOW;
+        if (fstatat(fd, filename, &a, flags) < 0)
+                return -errno;
+
+        if (fstatat(fd, "", &b, AT_EMPTY_PATH) < 0)
+                return -errno;
+
+        /* A directory with same device and inode as its parent? Must
+         * be the root directory */
+        if (a.st_dev == b.st_dev &&
+            a.st_ino == b.st_ino)
+                return 1;
+
+        return check_st_dev && (a.st_dev != b.st_dev);
+}
+
+/* flags can be AT_SYMLINK_FOLLOW or 0 */
+int path_is_mount_point(const char *t, int flags) {
+        _cleanup_close_ int fd = -1;
+        _cleanup_free_ char *canonical = NULL, *parent = NULL;
+
+        assert(t);
+
+        if (path_equal(t, "/"))
+                return 1;
+
+        /* we need to resolve symlinks manually, we can't just rely on
+         * fd_is_mount_point() to do that for us; if we have a structure like
+         * /bin -> /usr/bin/ and /usr is a mount point, then the parent that we
+         * look at needs to be /usr, not /. */
+        if (flags & AT_SYMLINK_FOLLOW) {
+                canonical = canonicalize_file_name(t);
+                if (!canonical)
+                        return -errno;
+
+                t = canonical;
+        }
+
+        parent = dirname_malloc(t);
+        if (!parent)
+                return -ENOMEM;
+
+        fd = openat(AT_FDCWD, parent, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_PATH);
+        if (fd < 0)
+                return -errno;
+
+        return fd_is_mount_point(fd, basename(t), flags);
+}
+
+int umount_recursive(const char *prefix, int flags) {
+        bool again;
+        int n = 0, r;
+
+        /* Try to umount everything recursively below a
+         * directory. Also, take care of stacked mounts, and keep
+         * unmounting them until they are gone. */
+
+        do {
+                _cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
+
+                again = false;
+                r = 0;
+
+                proc_self_mountinfo = fopen("/proc/self/mountinfo", "re");
+                if (!proc_self_mountinfo)
+                        return -errno;
+
+                for (;;) {
+                        _cleanup_free_ char *path = NULL, *p = NULL;
+                        int k;
+
+                        k = fscanf(proc_self_mountinfo,
+                                   "%*s "       /* (1) mount id */
+                                   "%*s "       /* (2) parent id */
+                                   "%*s "       /* (3) major:minor */
+                                   "%*s "       /* (4) root */
+                                   "%ms "       /* (5) mount point */
+                                   "%*s"        /* (6) mount options */
+                                   "%*[^-]"     /* (7) optional fields */
+                                   "- "         /* (8) separator */
+                                   "%*s "       /* (9) file system type */
+                                   "%*s"        /* (10) mount source */
+                                   "%*s"        /* (11) mount options 2 */
+                                   "%*[^\n]",   /* some rubbish at the end */
+                                   &path);
+                        if (k != 1) {
+                                if (k == EOF)
+                                        break;
+
+                                continue;
+                        }
+
+                        r = cunescape(path, UNESCAPE_RELAX, &p);
+                        if (r < 0)
+                                return r;
+
+                        if (!path_startswith(p, prefix))
+                                continue;
+
+                        if (umount2(p, flags) < 0) {
+                                r = -errno;
+                                continue;
+                        }
+
+                        again = true;
+                        n++;
+
+                        break;
+                }
+
+        } while (again);
+
+        return r ? r : n;
+}
+
+static int get_mount_flags(const char *path, unsigned long *flags) {
+        struct statvfs buf;
+
+        if (statvfs(path, &buf) < 0)
+                return -errno;
+        *flags = buf.f_flag;
+        return 0;
+}
+
+int bind_remount_recursive(const char *prefix, bool ro) {
+        _cleanup_set_free_free_ Set *done = NULL;
+        _cleanup_free_ char *cleaned = NULL;
+        int r;
+
+        /* Recursively remount a directory (and all its submounts)
+         * read-only or read-write. If the directory is already
+         * mounted, we reuse the mount and simply mark it
+         * MS_BIND|MS_RDONLY (or remove the MS_RDONLY for read-write
+         * operation). If it isn't we first make it one. Afterwards we
+         * apply MS_BIND|MS_RDONLY (or remove MS_RDONLY) to all
+         * submounts we can access, too. When mounts are stacked on
+         * the same mount point we only care for each individual
+         * "top-level" mount on each point, as we cannot
+         * influence/access the underlying mounts anyway. We do not
+         * have any effect on future submounts that might get
+         * propagated, they migt be writable. This includes future
+         * submounts that have been triggered via autofs. */
+
+        cleaned = strdup(prefix);
+        if (!cleaned)
+                return -ENOMEM;
+
+        path_kill_slashes(cleaned);
+
+        done = set_new(&string_hash_ops);
+        if (!done)
+                return -ENOMEM;
+
+        for (;;) {
+                _cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
+                _cleanup_set_free_free_ Set *todo = NULL;
+                bool top_autofs = false;
+                char *x;
+                unsigned long orig_flags;
+
+                todo = set_new(&string_hash_ops);
+                if (!todo)
+                        return -ENOMEM;
+
+                proc_self_mountinfo = fopen("/proc/self/mountinfo", "re");
+                if (!proc_self_mountinfo)
+                        return -errno;
+
+                for (;;) {
+                        _cleanup_free_ char *path = NULL, *p = NULL, *type = NULL;
+                        int k;
+
+                        k = fscanf(proc_self_mountinfo,
+                                   "%*s "       /* (1) mount id */
+                                   "%*s "       /* (2) parent id */
+                                   "%*s "       /* (3) major:minor */
+                                   "%*s "       /* (4) root */
+                                   "%ms "       /* (5) mount point */
+                                   "%*s"        /* (6) mount options (superblock) */
+                                   "%*[^-]"     /* (7) optional fields */
+                                   "- "         /* (8) separator */
+                                   "%ms "       /* (9) file system type */
+                                   "%*s"        /* (10) mount source */
+                                   "%*s"        /* (11) mount options (bind mount) */
+                                   "%*[^\n]",   /* some rubbish at the end */
+                                   &path,
+                                   &type);
+                        if (k != 2) {
+                                if (k == EOF)
+                                        break;
+
+                                continue;
+                        }
+
+                        r = cunescape(path, UNESCAPE_RELAX, &p);
+                        if (r < 0)
+                                return r;
+
+                        /* Let's ignore autofs mounts.  If they aren't
+                         * triggered yet, we want to avoid triggering
+                         * them, as we don't make any guarantees for
+                         * future submounts anyway.  If they are
+                         * already triggered, then we will find
+                         * another entry for this. */
+                        if (streq(type, "autofs")) {
+                                top_autofs = top_autofs || path_equal(cleaned, p);
+                                continue;
+                        }
+
+                        if (path_startswith(p, cleaned) &&
+                            !set_contains(done, p)) {
+
+                                r = set_consume(todo, p);
+                                p = NULL;
+
+                                if (r == -EEXIST)
+                                        continue;
+                                if (r < 0)
+                                        return r;
+                        }
+                }
+
+                /* If we have no submounts to process anymore and if
+                 * the root is either already done, or an autofs, we
+                 * are done */
+                if (set_isempty(todo) &&
+                    (top_autofs || set_contains(done, cleaned)))
+                        return 0;
+
+                if (!set_contains(done, cleaned) &&
+                    !set_contains(todo, cleaned)) {
+                        /* The prefix directory itself is not yet a
+                         * mount, make it one. */
+                        if (mount(cleaned, cleaned, NULL, MS_BIND|MS_REC, NULL) < 0)
+                                return -errno;
+
+                        orig_flags = 0;
+                        (void) get_mount_flags(cleaned, &orig_flags);
+                        orig_flags &= ~MS_RDONLY;
+
+                        if (mount(NULL, prefix, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0)
+                                return -errno;
+
+                        x = strdup(cleaned);
+                        if (!x)
+                                return -ENOMEM;
+
+                        r = set_consume(done, x);
+                        if (r < 0)
+                                return r;
+                }
+
+                while ((x = set_steal_first(todo))) {
+
+                        r = set_consume(done, x);
+                        if (r == -EEXIST || r == 0)
+                                continue;
+                        if (r < 0)
+                                return r;
+
+                        /* Try to reuse the original flag set, but
+                         * don't care for errors, in case of
+                         * obstructed mounts */
+                        orig_flags = 0;
+                        (void) get_mount_flags(x, &orig_flags);
+                        orig_flags &= ~MS_RDONLY;
+
+                        if (mount(NULL, x, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0) {
+
+                                /* Deal with mount points that are
+                                 * obstructed by a later mount */
+
+                                if (errno != ENOENT)
+                                        return -errno;
+                        }
+
+                }
+        }
+}
+
+int mount_move_root(const char *path) {
+        assert(path);
+
+        if (chdir(path) < 0)
+                return -errno;
+
+        if (mount(path, "/", NULL, MS_MOVE, NULL) < 0)
+                return -errno;
+
+        if (chroot(".") < 0)
+                return -errno;
+
+        if (chdir("/") < 0)
+                return -errno;
+
+        return 0;
+}