#include "strv.h"
#include "path-util.h"
#include "missing.h"
+#include "fileio.h"
bool path_is_absolute(const char *p) {
return p[0] == '/';
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) {
union file_handle_union h = FILE_HANDLE_INIT, h_parent = FILE_HANDLE_INIT;
int mount_id = -1, mount_id_parent = -1;
- bool nosupp = false;
+ bool nosupp = false, check_st_dev = false;
struct stat a, b;
int r;
assert(fd >= 0);
- /* We are not actually interested in the file handles, but
- * name_to_handle_at() also passes us the mount ID, hence use
- * it but throw the handle away */
+ /* 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 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, "", &h.handle, &mount_id, AT_EMPTY_PATH);
if (r < 0) {
if (errno == ENOSYS)
/* This kernel does not support name_to_handle_at()
- * fall back to the traditional stat() logic. */
- goto fallback;
+ * 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
if (nosupp)
/* Neither parent nor child do name_to_handle_at()?
We have no choice but to fall back. */
- goto fallback;
+ goto fallback_fdinfo;
else
/* The parent can't do name_to_handle_at() but the
* directory we are interested in can?
return 1;
} else
return -errno;
- } else if (nosupp)
- /* 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. */
+ }
+
+ /* 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;
- else {
- /* 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;
- }
+ /* 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:
- r = fstatat(fd, "", &a, AT_EMPTY_PATH);
+fallback_fdinfo:
+ r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id);
+ if (r == -EOPNOTSUPP)
+ goto fallback_fstat;
if (r < 0)
- return -errno;
+ return r;
- r = fstatat(fd, "..", &b, 0);
+ r = fd_fdinfo_mnt_id(fd, "..", 0, &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:
+ if (fstatat(fd, "", &a, AT_EMPTY_PATH) < 0)
+ return -errno;
+
+ if (fstatat(fd, "..", &b, 0) < 0)
return -errno;
/* A directory with same device and inode as its parent? Must
a.st_ino == b.st_ino)
return 1;
- return a.st_dev != b.st_dev;
+ return check_st_dev && (a.st_dev != b.st_dev);
}
int path_is_mount_point(const char *t, bool allow_symlink) {
~ianmdlvl / elogind.git / commitdiff