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mountpoint-util: make is_mount_point_at() take usual dir_fd + path style arguments

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This commit is contained in:
Yu Watanabe
2026-01-13 10:21:05 +09:00
parent a98a6eb95c
commit 7f6cf19513
7 changed files with 49 additions and 74 deletions
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src/basic/mountpoint-util.c
+34 -57
View File
@@ -163,29 +163,6 @@ static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *ret_mn
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);
}
bool file_handle_equal(const struct file_handle *a, const struct file_handle *b) {
if (a == b)
return true;
@@ -197,37 +174,30 @@ bool file_handle_equal(const struct file_handle *a, const struct file_handle *b)
return memcmp_nn(a->f_handle, a->handle_bytes, b->f_handle, b->handle_bytes) == 0;
}
int is_mount_point_at(int fd, const char *filename, int flags) {
int is_mount_point_at(int dir_fd, const char *path, int flags) {
int r;
assert(fd >= 0 || fd == AT_FDCWD);
assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
assert((flags & ~AT_SYMLINK_FOLLOW) == 0);
if (isempty(filename)) {
if (fd == AT_FDCWD)
filename = ".";
else {
/* If the file name is empty we'll see if the specified 'fd' is a mount point.
* That's only supported by 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 = "";
}
if (path_equal(path, "/"))
return true;
} else if (!STR_IN_SET(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. */
if (!filename_possibly_with_slash_suffix(filename))
return -EINVAL;
if (isempty(path)) {
if (dir_fd == AT_FDCWD)
path = ".";
else {
flags |= AT_EMPTY_PATH;
path = "";
}
}
struct statx sx = {}; /* explicitly initialize the struct to make msan silent. */
if (statx(fd, filename,
if (statx(dir_fd, path,
at_flags_normalize_nofollow(flags) |
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,
STATX_TYPE|STATX_INO,
&sx) < 0)
return -errno;
@@ -235,30 +205,37 @@ int is_mount_point_at(int fd, const char *filename, int flags) {
if (r < 0)
return r;
return FLAGS_SET(sx.stx_attributes, STATX_ATTR_MOUNT_ROOT);
if (FLAGS_SET(sx.stx_attributes, STATX_ATTR_MOUNT_ROOT))
return true;
/* When running on chroot environment, the root may not be a mount point, but we unconditionally
* return true when the input is "/" in the above, but the shortcut may not work e.g. when the path
* is relative. */
struct statx sx2 = {}; /* explicitly initialize the struct to make msan silent. */
if (statx(AT_FDCWD, "/", AT_STATX_DONT_SYNC, STATX_TYPE|STATX_INO, &sx2) < 0)
return -errno;
return statx_inode_same(&sx, &sx2);
}
/* flags can be AT_SYMLINK_FOLLOW or 0 */
int path_is_mount_point_full(const char *path, const char *root, int flags) {
_cleanup_close_ int dfd = -EBADF;
_cleanup_free_ char *fn = NULL;
_cleanup_close_ int dir_fd = -EBADF;
int r;
assert(path);
assert((flags & ~AT_SYMLINK_FOLLOW) == 0);
if (path_equal(path, "/"))
return 1;
if (empty_or_root(root))
return is_mount_point_at(AT_FDCWD, path, flags);
/* we need to resolve symlinks manually, we can't just rely on is_mount_point_at() 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 /. */
dfd = chase_and_open_parent(path, root,
CHASE_TRAIL_SLASH|(FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : CHASE_NOFOLLOW),
&fn);
if (dfd < 0)
return dfd;
r = chase(path, root,
FLAGS_SET(flags, AT_SYMLINK_FOLLOW) ? 0 : CHASE_NOFOLLOW,
/* ret_path= */ NULL, &dir_fd);
if (r < 0)
return r;
return is_mount_point_at(dfd, fn, flags);
return is_mount_point_at(dir_fd, /* path= */ NULL, flags);
}
int path_get_mnt_id_at_fallback(int dir_fd, const char *path, int *ret) {
src/basic/mountpoint-util.h
+1 -1
View File
@@ -45,7 +45,7 @@ static inline int path_get_mnt_id(const char *path, int *ret) {
return path_get_mnt_id_at(AT_FDCWD, path, ret);
}
int is_mount_point_at(int fd, const char *filename, int flags);
int is_mount_point_at(int dir_fd, const char *path, int flags);
int path_is_mount_point_full(const char *path, const char *root, int flags);
static inline int path_is_mount_point(const char *path) {
return path_is_mount_point_full(path, NULL, 0);