/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include #include #include #if WANT_LINUX_FS_H #include #endif #include "alloc-util.h" #include "chase.h" #include "fd-util.h" #include "fileio.h" #include "filesystems.h" #include "fs-util.h" #include "missing_fs.h" #include "missing_mount.h" #include "missing_stat.h" #include "missing_syscall.h" #include "mkdir.h" #include "mountpoint-util.h" #include "nulstr-util.h" #include "parse-util.h" #include "path-util.h" #include "stat-util.h" #include "stdio-util.h" #include "strv.h" #include "user-util.h" /* This is the original MAX_HANDLE_SZ definition from the kernel, when the API was introduced. We use that in place of * any more currently defined value to future-proof things: if the size is increased in the API headers, and our code * is recompiled then it would cease working on old kernels, as those refuse any sizes larger than this value with * EINVAL right-away. Hence, let's disconnect ourselves from any such API changes, and stick to the original definition * from when it was introduced. We use it as a start value only anyway (see below), and hence should be able to deal * with large file handles anyway. */ #define ORIGINAL_MAX_HANDLE_SZ 128 int name_to_handle_at_loop( int fd, const char *path, struct file_handle **ret_handle, int *ret_mnt_id, int flags) { size_t n = ORIGINAL_MAX_HANDLE_SZ; assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0); /* We need to invoke name_to_handle_at() in a loop, given that it might return EOVERFLOW when the specified * buffer is too small. Note that in contrast to what the docs might suggest, MAX_HANDLE_SZ is only good as a * start value, it is not an upper bound on the buffer size required. * * This improves on raw name_to_handle_at() also in one other regard: ret_handle and ret_mnt_id can be passed * as NULL if there's no interest in either. */ for (;;) { _cleanup_free_ struct file_handle *h = NULL; int mnt_id = -1; h = malloc0(offsetof(struct file_handle, f_handle) + n); if (!h) return -ENOMEM; h->handle_bytes = n; if (name_to_handle_at(fd, strempty(path), h, &mnt_id, flags) >= 0) { if (ret_handle) *ret_handle = TAKE_PTR(h); if (ret_mnt_id) *ret_mnt_id = mnt_id; return 0; } if (errno != EOVERFLOW) return -errno; if (!ret_handle && ret_mnt_id && mnt_id >= 0) { /* As it appears, name_to_handle_at() fills in mnt_id even when it returns EOVERFLOW when the * buffer is too small, but that's undocumented. Hence, let's make use of this if it appears to * be filled in, and the caller was interested in only the mount ID an nothing else. */ *ret_mnt_id = mnt_id; return 0; } /* If name_to_handle_at() didn't increase the byte size, then this EOVERFLOW is caused by something * else (apparently EOVERFLOW is returned for untriggered nfs4 mounts sometimes), not by the too small * buffer. In that case propagate EOVERFLOW */ if (h->handle_bytes <= n) return -EOVERFLOW; /* The buffer was too small. Size the new buffer by what name_to_handle_at() returned. */ n = h->handle_bytes; /* paranoia: check for overflow (note that .handle_bytes is unsigned only) */ if (n > UINT_MAX - offsetof(struct file_handle, f_handle)) return -EOVERFLOW; } } static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *ret_mnt_id) { char path[STRLEN("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)]; _cleanup_free_ char *fdinfo = NULL; _cleanup_close_ int subfd = -EBADF; char *p; int r; assert(ret_mnt_id); assert((flags & ~(AT_SYMLINK_FOLLOW|AT_EMPTY_PATH)) == 0); if ((flags & AT_EMPTY_PATH) && isempty(filename)) xsprintf(path, "/proc/self/fdinfo/%i", fd); else { subfd = openat(fd, filename, O_CLOEXEC|O_PATH|(flags & AT_SYMLINK_FOLLOW ? 0 : O_NOFOLLOW)); if (subfd < 0) return -errno; xsprintf(path, "/proc/self/fdinfo/%i", subfd); } r = read_full_virtual_file(path, &fdinfo, NULL); if (r == -ENOENT) /* The fdinfo directory is a relatively new addition */ return proc_mounted() > 0 ? -EOPNOTSUPP : -ENOSYS; if (r < 0) return r; p = find_line_startswith(fdinfo, "mnt_id:"); if (!p) /* The mnt_id field is a relatively new addition */ return -EOPNOTSUPP; p += strspn(p, WHITESPACE); p[strcspn(p, WHITESPACE)] = 0; return safe_atoi(p, ret_mnt_id); } static bool filename_possibly_with_slash_suffix(const char *s) { const char *slash, *copied; /* Checks whether the specified string is either file name, or a filename with a suffix of * slashes. But nothing else. * * this is OK: foo, bar, foo/, bar/, foo//, bar/// * this is not OK: "", "/", "/foo", "foo/bar", ".", ".." … */ slash = strchr(s, '/'); if (!slash) return filename_is_valid(s); if (slash - s > PATH_MAX) /* We want to allocate on the stack below, hence do a size check first */ return false; if (slash[strspn(slash, "/")] != 0) /* Check that the suffix consist only of one or more slashes */ return false; copied = strndupa_safe(s, slash - s); return filename_is_valid(copied); } static bool is_name_to_handle_at_fatal_error(int err) { /* name_to_handle_at() can return "acceptable" errors that are due to the context. For * example the kernel does not support name_to_handle_at() at all (ENOSYS), or the syscall * was blocked (EACCES/EPERM; maybe through seccomp, because we are running inside of a * container), or the mount point is not triggered yet (EOVERFLOW, think nfs4), or some * general name_to_handle_at() flakiness (EINVAL). However other errors are not supposed to * happen and therefore are considered fatal ones. */ assert(err < 0); return !IN_SET(err, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL); } int fd_is_mount_point(int fd, const char *filename, int flags) { _cleanup_free_ struct file_handle *h = NULL, *h_parent = NULL; int mount_id = -1, mount_id_parent = -1; bool nosupp = false, check_st_dev = true; STRUCT_STATX_DEFINE(sx); struct stat a, b; int r; assert(fd >= 0); assert((flags & ~AT_SYMLINK_FOLLOW) == 0); if (!filename) { /* If the file name is specified as NULL we'll see if the specified 'fd' is a mount * point. That's only supported if the kernel supports statx(), or if the inode specified via * 'fd' refers to a directory. Otherwise, we'll have to fail (ENOTDIR), because we have no * kernel API to query the information we need. */ flags |= AT_EMPTY_PATH; filename = ""; } else if (!filename_possibly_with_slash_suffix(filename)) /* Insist that the specified filename is actually a filename, and not a path, i.e. some inode further * up or down the tree then immediately below the specified directory fd. */ return -EINVAL; /* First we will try statx()' STATX_ATTR_MOUNT_ROOT attribute, which is our ideal API, available * since kernel 5.8. * * If that fails, our second try is 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/. 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 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. */ if (statx(fd, filename, (FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : AT_SYMLINK_NOFOLLOW) | (flags & AT_EMPTY_PATH) | AT_NO_AUTOMOUNT | /* don't trigger automounts – mounts are a local concept, hence no need to trigger automounts to determine STATX_ATTR_MOUNT_ROOT */ AT_STATX_DONT_SYNC, /* don't go to the network for this – for similar reasons */ STATX_TYPE, &sx) < 0) { if (!ERRNO_IS_NOT_SUPPORTED(errno) && /* statx() is not supported by the kernel. */ !ERRNO_IS_PRIVILEGE(errno) && /* maybe filtered by seccomp. */ errno != EINVAL) /* glibc's fallback method returns EINVAL when AT_STATX_DONT_SYNC is set. */ return -errno; /* If statx() is not available or forbidden, fall back to name_to_handle_at() below */ } else if (FLAGS_SET(sx.stx_attributes_mask, STATX_ATTR_MOUNT_ROOT)) /* yay! */ return FLAGS_SET(sx.stx_attributes, STATX_ATTR_MOUNT_ROOT); r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags); if (r < 0) { if (is_name_to_handle_at_fatal_error(r)) return r; if (r != -EOPNOTSUPP) goto fallback_fdinfo; /* 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 fall * back to the traditional stat() logic */ nosupp = true; } if (isempty(filename)) r = name_to_handle_at_loop(fd, "..", &h_parent, &mount_id_parent, 0); /* can't work for non-directories 😢 */ else r = name_to_handle_at_loop(fd, "", &h_parent, &mount_id_parent, AT_EMPTY_PATH); if (r < 0) { if (is_name_to_handle_at_fatal_error(r)) return r; if (r != -EOPNOTSUPP) goto fallback_fdinfo; if (nosupp) /* Both the parent and the directory can't do name_to_handle_at() */ goto fallback_fdinfo; /* 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; } /* 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_type == h_parent->handle_type && memcmp_nn(h->f_handle, h->handle_bytes, h_parent->f_handle, h_parent->handle_bytes) == 0) return 1; return mount_id != mount_id_parent; fallback_fdinfo: r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id); if (IN_SET(r, -EOPNOTSUPP, -EACCES, -EPERM, -ENOSYS)) goto fallback_fstat; if (r < 0) return r; if (isempty(filename)) r = fd_fdinfo_mnt_id(fd, "..", 0, &mount_id_parent); /* can't work for non-directories 😢 */ else 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 (isempty(filename)) r = fstatat(fd, "..", &b, 0); else r = fstatat(fd, "", &b, AT_EMPTY_PATH); if (r < 0) return -errno; /* A directory with same device and inode as its parent? Must be the root directory */ if (stat_inode_same(&a, &b)) 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, const char *root, int flags) { _cleanup_free_ char *canonical = NULL; _cleanup_close_ int fd = -EBADF; int r; assert(t); assert((flags & ~AT_SYMLINK_FOLLOW) == 0); 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) { r = chase(t, root, CHASE_TRAIL_SLASH, &canonical, NULL); if (r < 0) return r; t = canonical; } fd = open_parent(t, O_PATH|O_CLOEXEC, 0); if (fd < 0) return fd; return fd_is_mount_point(fd, last_path_component(t), flags); } int path_get_mnt_id_at_fallback(int dir_fd, const char *path, int *ret) { int r; assert(dir_fd >= 0 || dir_fd == AT_FDCWD); assert(ret); r = name_to_handle_at_loop(dir_fd, path, NULL, ret, isempty(path) ? AT_EMPTY_PATH : 0); if (r == 0 || is_name_to_handle_at_fatal_error(r)) return r; return fd_fdinfo_mnt_id(dir_fd, path, isempty(path) ? AT_EMPTY_PATH : 0, ret); } int path_get_mnt_id_at(int dir_fd, const char *path, int *ret) { STRUCT_NEW_STATX_DEFINE(buf); assert(dir_fd >= 0 || dir_fd == AT_FDCWD); assert(ret); if (statx(dir_fd, strempty(path), (isempty(path) ? AT_EMPTY_PATH : AT_SYMLINK_NOFOLLOW) | AT_NO_AUTOMOUNT | /* don't trigger automounts, mnt_id is a local concept */ AT_STATX_DONT_SYNC, /* don't go to the network, mnt_id is a local concept */ STATX_MNT_ID, &buf.sx) < 0) { if (!ERRNO_IS_NOT_SUPPORTED(errno) && /* statx() is not supported by the kernel. */ !ERRNO_IS_PRIVILEGE(errno) && /* maybe filtered by seccomp. */ errno != EINVAL) /* glibc's fallback method returns EINVAL when AT_STATX_DONT_SYNC is set. */ return -errno; /* Fall back to name_to_handle_at() and then fdinfo if statx is not supported or we lack * privileges */ } else if (FLAGS_SET(buf.nsx.stx_mask, STATX_MNT_ID)) { *ret = buf.nsx.stx_mnt_id; return 0; } return path_get_mnt_id_at_fallback(dir_fd, path, ret); } bool fstype_is_network(const char *fstype) { const char *x; x = startswith(fstype, "fuse."); if (x) fstype = x; if (nulstr_contains(filesystem_sets[FILESYSTEM_SET_NETWORK].value, fstype)) return true; /* Filesystems not present in the internal database */ return STR_IN_SET(fstype, "davfs", "glusterfs", "lustre", "sshfs"); } bool fstype_needs_quota(const char *fstype) { /* 1. quotacheck needs to be run for some filesystems after they are mounted * if the filesystem was not unmounted cleanly. * 2. You may need to run quotaon to enable quota usage tracking and/or * enforcement. * ext2 - needs 1) and 2) * ext3 - needs 2) if configured using usrjquota/grpjquota mount options * ext4 - needs 1) if created without journal, needs 2) if created without QUOTA * filesystem feature * reiserfs - needs 2). * jfs - needs 2) * f2fs - needs 2) if configured using usrjquota/grpjquota/prjjquota mount options * xfs - nothing needed * gfs2 - nothing needed * ocfs2 - nothing needed * btrfs - nothing needed * for reference see filesystem and quota manpages */ return STR_IN_SET(fstype, "ext2", "ext3", "ext4", "reiserfs", "jfs", "f2fs"); } bool fstype_is_api_vfs(const char *fstype) { const FilesystemSet *fs; FOREACH_POINTER(fs, filesystem_sets + FILESYSTEM_SET_BASIC_API, filesystem_sets + FILESYSTEM_SET_AUXILIARY_API, filesystem_sets + FILESYSTEM_SET_PRIVILEGED_API, filesystem_sets + FILESYSTEM_SET_TEMPORARY) if (nulstr_contains(fs->value, fstype)) return true; /* Filesystems not present in the internal database */ return STR_IN_SET(fstype, "autofs", "cpuset", "devtmpfs"); } bool fstype_is_blockdev_backed(const char *fstype) { const char *x; x = startswith(fstype, "fuse."); if (x) fstype = x; return !streq(fstype, "9p") && !fstype_is_network(fstype) && !fstype_is_api_vfs(fstype); } bool fstype_is_ro(const char *fstype) { /* All Linux file systems that are necessarily read-only */ return STR_IN_SET(fstype, "DM_verity_hash", "cramfs", "erofs", "iso9660", "squashfs"); } bool fstype_can_discard(const char *fstype) { assert(fstype); /* Use a curated list as first check, to avoid calling fsopen() which might load kmods, which might * not be allowed in our MAC context. */ if (STR_IN_SET(fstype, "btrfs", "f2fs", "ext4", "vfat", "xfs")) return true; /* On new kernels we can just ask the kernel */ return mount_option_supported(fstype, "discard", NULL) > 0; } const char* fstype_norecovery_option(const char *fstype) { int r; assert(fstype); /* Use a curated list as first check, to avoid calling fsopen() which might load kmods, which might * not be allowed in our MAC context. */ if (STR_IN_SET(fstype, "ext3", "ext4", "xfs")) return "norecovery"; /* btrfs dropped support for the "norecovery" option in 6.8 * (https://github.com/torvalds/linux/commit/a1912f712188291f9d7d434fba155461f1ebef66) and replaced * it with rescue=nologreplay, so we check for the new name first and fall back to checking for the * old name if the new name doesn't work. */ if (streq(fstype, "btrfs")) { r = mount_option_supported(fstype, "rescue=nologreplay", NULL); if (r == -EAGAIN) { log_debug_errno(r, "Failed to check for btrfs 'rescue=nologreplay' option, assuming old kernel with 'norecovery': %m"); return "norecovery"; } if (r < 0) log_debug_errno(r, "Failed to check for btrfs 'rescue=nologreplay' option, assuming it is not supported: %m"); if (r > 0) return "rescue=nologreplay"; } /* On new kernels we can just ask the kernel */ return mount_option_supported(fstype, "norecovery", NULL) > 0 ? "norecovery" : NULL; } bool fstype_can_umask(const char *fstype) { assert(fstype); /* Use a curated list as first check, to avoid calling fsopen() which might load kmods, which might * not be allowed in our MAC context. If we don't know ourselves, on new kernels we can just ask the * kernel. */ return streq(fstype, "vfat") || mount_option_supported(fstype, "umask", "0077") > 0; } bool fstype_can_uid_gid(const char *fstype) { /* All file systems that have a uid=/gid= mount option that fixates the owners of all files and * directories, current and future. Note that this does *not* ask the kernel via * mount_option_supported() here because the uid=/gid= setting of various file systems mean different * things: some apply it only to the root dir inode, others to all inodes in the file system. Thus we * maintain the curated list below. 😢 */ return STR_IN_SET(fstype, "adfs", "exfat", "fat", "hfs", "hpfs", "iso9660", "msdos", "ntfs", "vfat"); } int dev_is_devtmpfs(void) { _cleanup_fclose_ FILE *proc_self_mountinfo = NULL; int mount_id, r; char *e; r = path_get_mnt_id("/dev", &mount_id); if (r < 0) return r; r = fopen_unlocked("/proc/self/mountinfo", "re", &proc_self_mountinfo); if (r == -ENOENT) return proc_mounted() > 0 ? -ENOENT : -ENOSYS; if (r < 0) return r; for (;;) { _cleanup_free_ char *line = NULL; int mid; r = read_line(proc_self_mountinfo, LONG_LINE_MAX, &line); if (r < 0) return r; if (r == 0) break; if (sscanf(line, "%i", &mid) != 1) continue; if (mid != mount_id) continue; e = strstrafter(line, " - "); if (!e) continue; /* accept any name that starts with the currently expected type */ if (startswith(e, "devtmpfs")) return true; } return false; } int mount_fd(const char *source, int target_fd, const char *filesystemtype, unsigned long mountflags, const void *data) { if (mount(source, FORMAT_PROC_FD_PATH(target_fd), filesystemtype, mountflags, data) < 0) { if (errno != ENOENT) return -errno; /* ENOENT can mean two things: either that the source is missing, or that /proc/ isn't * mounted. Check for the latter to generate better error messages. */ if (proc_mounted() == 0) return -ENOSYS; return -ENOENT; } return 0; } int mount_nofollow( const char *source, const char *target, const char *filesystemtype, unsigned long mountflags, const void *data) { _cleanup_close_ int fd = -EBADF; /* In almost all cases we want to manipulate the mount table without following symlinks, hence * mount_nofollow() is usually the way to go. The only exceptions are environments where /proc/ is * not available yet, since we need /proc/self/fd/ for this logic to work. i.e. during the early * initialization of namespacing/container stuff where /proc is not yet mounted (and maybe even the * fs to mount) we can only use traditional mount() directly. * * Note that this disables following only for the final component of the target, i.e symlinks within * the path of the target are honoured, as are symlinks in the source path everywhere. */ fd = open(target, O_PATH|O_CLOEXEC|O_NOFOLLOW); if (fd < 0) return -errno; return mount_fd(source, fd, filesystemtype, mountflags, data); } const char *mount_propagation_flag_to_string(unsigned long flags) { switch (flags & (MS_SHARED|MS_SLAVE|MS_PRIVATE)) { case 0: return ""; case MS_SHARED: return "shared"; case MS_SLAVE: return "slave"; case MS_PRIVATE: return "private"; } return NULL; } int mount_propagation_flag_from_string(const char *name, unsigned long *ret) { if (isempty(name)) *ret = 0; else if (streq(name, "shared")) *ret = MS_SHARED; else if (streq(name, "slave")) *ret = MS_SLAVE; else if (streq(name, "private")) *ret = MS_PRIVATE; else return -EINVAL; return 0; } bool mount_propagation_flag_is_valid(unsigned long flag) { return IN_SET(flag, 0, MS_SHARED, MS_PRIVATE, MS_SLAVE); } bool mount_new_api_supported(void) { static int cache = -1; int r; if (cache >= 0) return cache; /* This is the newer API among the ones we use, so use it as boundary */ r = RET_NERRNO(mount_setattr(-EBADF, NULL, 0, NULL, 0)); if (r == 0 || ERRNO_IS_NOT_SUPPORTED(r)) /* This should return an error if it is working properly */ return (cache = false); return (cache = true); } unsigned long ms_nosymfollow_supported(void) { _cleanup_close_ int fsfd = -EBADF, mntfd = -EBADF; static int cache = -1; /* Returns MS_NOSYMFOLLOW if it is supported, zero otherwise. */ if (cache >= 0) return cache ? MS_NOSYMFOLLOW : 0; if (!mount_new_api_supported()) goto not_supported; /* Checks if MS_NOSYMFOLLOW is supported (which was added in 5.10). We use the new mount API's * mount_setattr() call for that, which was added in 5.12, which is close enough. */ fsfd = fsopen("tmpfs", FSOPEN_CLOEXEC); if (fsfd < 0) { if (ERRNO_IS_NOT_SUPPORTED(errno)) goto not_supported; log_debug_errno(errno, "Failed to open superblock context for tmpfs: %m"); return 0; } if (fsconfig(fsfd, FSCONFIG_CMD_CREATE, NULL, NULL, 0) < 0) { if (ERRNO_IS_NOT_SUPPORTED(errno)) goto not_supported; log_debug_errno(errno, "Failed to create tmpfs superblock: %m"); return 0; } mntfd = fsmount(fsfd, FSMOUNT_CLOEXEC, 0); if (mntfd < 0) { if (ERRNO_IS_NOT_SUPPORTED(errno)) goto not_supported; log_debug_errno(errno, "Failed to turn superblock fd into mount fd: %m"); return 0; } if (mount_setattr(mntfd, "", AT_EMPTY_PATH|AT_RECURSIVE, &(struct mount_attr) { .attr_set = MOUNT_ATTR_NOSYMFOLLOW, }, sizeof(struct mount_attr)) < 0) { if (ERRNO_IS_NOT_SUPPORTED(errno)) goto not_supported; log_debug_errno(errno, "Failed to set MOUNT_ATTR_NOSYMFOLLOW mount attribute: %m"); return 0; } cache = true; return MS_NOSYMFOLLOW; not_supported: cache = false; return 0; } int mount_option_supported(const char *fstype, const char *key, const char *value) { _cleanup_close_ int fd = -EBADF; int r; /* Checks if the specified file system supports a mount option. Returns > 0 if it supports it, == 0 if * it does not. Return -EAGAIN if we can't determine it. And any other error otherwise. */ assert(fstype); assert(key); fd = fsopen(fstype, FSOPEN_CLOEXEC); if (fd < 0) { if (ERRNO_IS_NOT_SUPPORTED(errno)) return -EAGAIN; /* new mount API not available → don't know */ return log_debug_errno(errno, "Failed to open superblock context for '%s': %m", fstype); } /* Various file systems have not been converted to the new mount API yet. For such file systems * fsconfig() with FSCONFIG_SET_STRING/FSCONFIG_SET_FLAG never fail. Which sucks, because we want to * use it for testing support, after all. Let's hence do a check if the file system got converted yet * first. */ if (fsconfig(fd, FSCONFIG_SET_FD, "adefinitelynotexistingmountoption", NULL, fd) < 0) { /* If FSCONFIG_SET_FD is not supported for the fs, then the file system was not converted to * the new mount API yet. If it returns EINVAL the mount option doesn't exist, but the fstype * is converted. */ if (errno == EOPNOTSUPP) return -EAGAIN; /* FSCONFIG_SET_FD not supported on the fs, hence not converted to new mount API → don't know */ if (errno != EINVAL) return log_debug_errno(errno, "Failed to check if file system has been converted to new mount API: %m"); /* So FSCONFIG_SET_FD worked, but the option didn't exist (we got EINVAL), this means the fs * is converted. Let's now ask the actual question we wonder about. */ } else return log_debug_errno(SYNTHETIC_ERRNO(EAGAIN), "FSCONFIG_SET_FD worked unexpectedly for '%s', whoa!", fstype); if (value) r = fsconfig(fd, FSCONFIG_SET_STRING, key, value, 0); else r = fsconfig(fd, FSCONFIG_SET_FLAG, key, NULL, 0); if (r < 0) { if (errno == EINVAL) return false; /* EINVAL means option not supported. */ return log_debug_errno(errno, "Failed to set '%s%s%s' on '%s' superblock context: %m", key, value ? "=" : "", strempty(value), fstype); } return true; /* works! */ }