util-lib: move mount related utility calls to mount-util.[ch]
This commit is contained in:
Lennart Poettering
@@ -454,205 +454,6 @@ char* path_join(const char *root, const char *path, const char *rest) {
|
||||
NULL);
|
||||
}
|
||||
|
||||
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 path_is_read_only_fs(const char *path) {
|
||||
struct statvfs st;
|
||||
|
||||
|
||||
Reference in New Issue
Block a user