ac2474e4ff
The function returns true if the specified filesystem requires a block device.
455 lines
16 KiB
C
455 lines
16 KiB
C
/* SPDX-License-Identifier: LGPL-2.1+ */
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#include <errno.h>
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#include <fcntl.h>
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#include <sys/mount.h>
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#include "alloc-util.h"
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#include "fd-util.h"
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#include "fileio.h"
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#include "fs-util.h"
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#include "mountpoint-util.h"
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#include "parse-util.h"
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#include "path-util.h"
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#include "stdio-util.h"
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#include "strv.h"
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/* This is the original MAX_HANDLE_SZ definition from the kernel, when the API was introduced. We use that in place of
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* any more currently defined value to future-proof things: if the size is increased in the API headers, and our code
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* is recompiled then it would cease working on old kernels, as those refuse any sizes larger than this value with
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* EINVAL right-away. Hence, let's disconnect ourselves from any such API changes, and stick to the original definition
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* from when it was introduced. We use it as a start value only anyway (see below), and hence should be able to deal
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* with large file handles anyway. */
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#define ORIGINAL_MAX_HANDLE_SZ 128
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int name_to_handle_at_loop(
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int fd,
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const char *path,
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struct file_handle **ret_handle,
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int *ret_mnt_id,
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int flags) {
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_cleanup_free_ struct file_handle *h = NULL;
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size_t n = ORIGINAL_MAX_HANDLE_SZ;
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/* We need to invoke name_to_handle_at() in a loop, given that it might return EOVERFLOW when the specified
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* buffer is too small. Note that in contrast to what the docs might suggest, MAX_HANDLE_SZ is only good as a
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* start value, it is not an upper bound on the buffer size required.
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*
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* This improves on raw name_to_handle_at() also in one other regard: ret_handle and ret_mnt_id can be passed
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* as NULL if there's no interest in either. */
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for (;;) {
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int mnt_id = -1;
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h = malloc0(offsetof(struct file_handle, f_handle) + n);
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if (!h)
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return -ENOMEM;
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h->handle_bytes = n;
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if (name_to_handle_at(fd, path, h, &mnt_id, flags) >= 0) {
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if (ret_handle)
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*ret_handle = TAKE_PTR(h);
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if (ret_mnt_id)
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*ret_mnt_id = mnt_id;
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return 0;
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}
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if (errno != EOVERFLOW)
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return -errno;
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if (!ret_handle && ret_mnt_id && mnt_id >= 0) {
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/* As it appears, name_to_handle_at() fills in mnt_id even when it returns EOVERFLOW when the
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* buffer is too small, but that's undocumented. Hence, let's make use of this if it appears to
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* be filled in, and the caller was interested in only the mount ID an nothing else. */
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*ret_mnt_id = mnt_id;
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return 0;
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}
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/* If name_to_handle_at() didn't increase the byte size, then this EOVERFLOW is caused by something
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* else (apparently EOVERFLOW is returned for untriggered nfs4 mounts sometimes), not by the too small
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* buffer. In that case propagate EOVERFLOW */
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if (h->handle_bytes <= n)
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return -EOVERFLOW;
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/* The buffer was too small. Size the new buffer by what name_to_handle_at() returned. */
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n = h->handle_bytes;
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if (offsetof(struct file_handle, f_handle) + n < n) /* check for addition overflow */
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return -EOVERFLOW;
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h = mfree(h);
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}
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}
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static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id) {
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char path[STRLEN("/proc/self/fdinfo/") + DECIMAL_STR_MAX(int)];
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_cleanup_free_ char *fdinfo = NULL;
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_cleanup_close_ int subfd = -1;
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char *p;
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int r;
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if ((flags & AT_EMPTY_PATH) && isempty(filename))
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xsprintf(path, "/proc/self/fdinfo/%i", fd);
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else {
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subfd = openat(fd, filename, O_CLOEXEC|O_PATH|(flags & AT_SYMLINK_FOLLOW ? 0 : O_NOFOLLOW));
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if (subfd < 0)
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return -errno;
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xsprintf(path, "/proc/self/fdinfo/%i", subfd);
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}
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r = read_full_file(path, &fdinfo, NULL);
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if (r == -ENOENT) /* The fdinfo directory is a relatively new addition */
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return -EOPNOTSUPP;
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if (r < 0)
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return r;
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p = startswith(fdinfo, "mnt_id:");
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if (!p) {
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p = strstr(fdinfo, "\nmnt_id:");
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if (!p) /* The mnt_id field is a relatively new addition */
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return -EOPNOTSUPP;
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p += 8;
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}
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p += strspn(p, WHITESPACE);
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p[strcspn(p, WHITESPACE)] = 0;
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return safe_atoi(p, mnt_id);
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}
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int fd_is_mount_point(int fd, const char *filename, int flags) {
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_cleanup_free_ struct file_handle *h = NULL, *h_parent = NULL;
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int mount_id = -1, mount_id_parent = -1;
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bool nosupp = false, check_st_dev = true;
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struct stat a, b;
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int r;
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assert(fd >= 0);
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assert(filename);
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/* First we will try the name_to_handle_at() syscall, which
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* tells us the mount id and an opaque file "handle". It is
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* not supported everywhere though (kernel compile-time
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* option, not all file systems are hooked up). If it works
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* the mount id is usually good enough to tell us whether
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* something is a mount point.
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*
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* If that didn't work we will try to read the mount id from
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* /proc/self/fdinfo/<fd>. This is almost as good as
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* name_to_handle_at(), however, does not return the
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* opaque file handle. The opaque file handle is pretty useful
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* to detect the root directory, which we should always
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* consider a mount point. Hence we use this only as
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* fallback. Exporting the mnt_id in fdinfo is a pretty recent
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* kernel addition.
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*
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* As last fallback we do traditional fstat() based st_dev
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* comparisons. This is how things were traditionally done,
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* but unionfs breaks this since it exposes file
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* systems with a variety of st_dev reported. Also, btrfs
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* subvolumes have different st_dev, even though they aren't
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* real mounts of their own. */
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r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags);
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if (IN_SET(r, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL))
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/* This kernel does not support name_to_handle_at() at all (ENOSYS), or the syscall was blocked
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* (EACCES/EPERM; maybe through seccomp, because we are running inside of a container?), or the mount
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* point is not triggered yet (EOVERFLOW, think nfs4), or some general name_to_handle_at() flakiness
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* (EINVAL): fall back to simpler logic. */
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goto fallback_fdinfo;
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else if (r == -EOPNOTSUPP)
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/* This kernel or file system does not support name_to_handle_at(), hence let's see if the upper fs
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* supports it (in which case it is a mount point), otherwise fallback to the traditional stat()
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* logic */
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nosupp = true;
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else if (r < 0)
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return r;
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r = name_to_handle_at_loop(fd, "", &h_parent, &mount_id_parent, AT_EMPTY_PATH);
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if (r == -EOPNOTSUPP) {
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if (nosupp)
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/* Neither parent nor child do name_to_handle_at()? We have no choice but to fall back. */
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goto fallback_fdinfo;
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else
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/* The parent can't do name_to_handle_at() but the directory we are interested in can? If so,
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* it must be a mount point. */
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return 1;
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} else if (r < 0)
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return r;
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/* The parent can do name_to_handle_at() but the
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* directory we are interested in can't? If so, it
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* must be a mount point. */
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if (nosupp)
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return 1;
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/* If the file handle for the directory we are
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* interested in and its parent are identical, we
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* assume this is the root directory, which is a mount
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* point. */
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if (h->handle_bytes == h_parent->handle_bytes &&
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h->handle_type == h_parent->handle_type &&
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memcmp(h->f_handle, h_parent->f_handle, h->handle_bytes) == 0)
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return 1;
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return mount_id != mount_id_parent;
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fallback_fdinfo:
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r = fd_fdinfo_mnt_id(fd, filename, flags, &mount_id);
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if (IN_SET(r, -EOPNOTSUPP, -EACCES, -EPERM))
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goto fallback_fstat;
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if (r < 0)
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return r;
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r = fd_fdinfo_mnt_id(fd, "", AT_EMPTY_PATH, &mount_id_parent);
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if (r < 0)
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return r;
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if (mount_id != mount_id_parent)
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return 1;
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/* Hmm, so, the mount ids are the same. This leaves one
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* special case though for the root file system. For that,
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* let's see if the parent directory has the same inode as we
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* are interested in. Hence, let's also do fstat() checks now,
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* too, but avoid the st_dev comparisons, since they aren't
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* that useful on unionfs mounts. */
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check_st_dev = false;
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fallback_fstat:
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/* yay for fstatat() taking a different set of flags than the other
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* _at() above */
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if (flags & AT_SYMLINK_FOLLOW)
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flags &= ~AT_SYMLINK_FOLLOW;
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else
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flags |= AT_SYMLINK_NOFOLLOW;
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if (fstatat(fd, filename, &a, flags) < 0)
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return -errno;
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if (fstatat(fd, "", &b, AT_EMPTY_PATH) < 0)
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return -errno;
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/* A directory with same device and inode as its parent? Must
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* be the root directory */
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if (a.st_dev == b.st_dev &&
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a.st_ino == b.st_ino)
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return 1;
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return check_st_dev && (a.st_dev != b.st_dev);
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}
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/* flags can be AT_SYMLINK_FOLLOW or 0 */
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int path_is_mount_point(const char *t, const char *root, int flags) {
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_cleanup_free_ char *canonical = NULL;
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_cleanup_close_ int fd = -1;
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int r;
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assert(t);
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assert((flags & ~AT_SYMLINK_FOLLOW) == 0);
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if (path_equal(t, "/"))
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return 1;
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/* we need to resolve symlinks manually, we can't just rely on
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* fd_is_mount_point() to do that for us; if we have a structure like
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* /bin -> /usr/bin/ and /usr is a mount point, then the parent that we
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* look at needs to be /usr, not /. */
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if (flags & AT_SYMLINK_FOLLOW) {
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r = chase_symlinks(t, root, CHASE_TRAIL_SLASH, &canonical, NULL);
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if (r < 0)
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return r;
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t = canonical;
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}
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fd = open_parent(t, O_PATH|O_CLOEXEC, 0);
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if (fd < 0)
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return -errno;
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return fd_is_mount_point(fd, last_path_component(t), flags);
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}
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int path_get_mnt_id(const char *path, int *ret) {
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int r;
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r = name_to_handle_at_loop(AT_FDCWD, path, NULL, ret, 0);
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if (IN_SET(r, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL)) /* kernel/fs don't support this, or seccomp blocks access, or untriggered mount, or name_to_handle_at() is flaky */
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return fd_fdinfo_mnt_id(AT_FDCWD, path, 0, ret);
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return r;
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}
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bool fstype_is_network(const char *fstype) {
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const char *x;
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x = startswith(fstype, "fuse.");
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if (x)
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fstype = x;
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return STR_IN_SET(fstype,
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"afs",
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"ceph",
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"cifs",
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"smb3",
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"smbfs",
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"sshfs",
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"ncpfs",
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"ncp",
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"nfs",
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"nfs4",
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"gfs",
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"gfs2",
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"glusterfs",
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"pvfs2", /* OrangeFS */
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"ocfs2",
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"lustre",
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"davfs");
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}
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bool fstype_is_api_vfs(const char *fstype) {
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return STR_IN_SET(fstype,
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"autofs",
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"bpf",
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"cgroup",
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"cgroup2",
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"configfs",
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"cpuset",
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"debugfs",
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"devpts",
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"devtmpfs",
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"efivarfs",
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"fusectl",
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"hugetlbfs",
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"mqueue",
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"proc",
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"pstore",
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"ramfs",
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"securityfs",
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"sysfs",
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"tmpfs",
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"tracefs");
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}
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bool fstype_is_blockdev_backed(const char *fstype) {
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const char *x;
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x = startswith(fstype, "fuse.");
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if (x)
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fstype = x;
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return !streq(fstype, "9p") && !fstype_is_network(fstype) && !fstype_is_api_vfs(fstype);
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}
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bool fstype_is_ro(const char *fstype) {
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/* All Linux file systems that are necessarily read-only */
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return STR_IN_SET(fstype,
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"DM_verity_hash",
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"iso9660",
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"squashfs");
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}
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bool fstype_can_discard(const char *fstype) {
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return STR_IN_SET(fstype,
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"btrfs",
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"ext4",
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"vfat",
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"xfs");
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}
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bool fstype_can_uid_gid(const char *fstype) {
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/* All file systems that have a uid=/gid= mount option that fixates the owners of all files and directories,
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* current and future. */
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return STR_IN_SET(fstype,
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"adfs",
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"exfat",
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"fat",
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"hfs",
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"hpfs",
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"iso9660",
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"msdos",
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"ntfs",
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"vfat");
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}
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int dev_is_devtmpfs(void) {
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_cleanup_fclose_ FILE *proc_self_mountinfo = NULL;
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int mount_id, r;
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char *e;
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r = path_get_mnt_id("/dev", &mount_id);
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if (r < 0)
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return r;
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r = fopen_unlocked("/proc/self/mountinfo", "re", &proc_self_mountinfo);
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if (r < 0)
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return r;
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for (;;) {
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_cleanup_free_ char *line = NULL;
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int mid;
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r = read_line(proc_self_mountinfo, LONG_LINE_MAX, &line);
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if (r < 0)
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return r;
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if (r == 0)
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break;
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if (sscanf(line, "%i", &mid) != 1)
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continue;
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if (mid != mount_id)
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continue;
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e = strstr(line, " - ");
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if (!e)
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continue;
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/* accept any name that starts with the currently expected type */
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if (startswith(e + 3, "devtmpfs"))
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return true;
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}
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return false;
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}
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const char *mount_propagation_flags_to_string(unsigned long flags) {
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switch (flags & (MS_SHARED|MS_SLAVE|MS_PRIVATE)) {
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case 0:
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return "";
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case MS_SHARED:
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return "shared";
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case MS_SLAVE:
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return "slave";
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case MS_PRIVATE:
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return "private";
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}
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return NULL;
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}
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int mount_propagation_flags_from_string(const char *name, unsigned long *ret) {
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if (isempty(name))
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*ret = 0;
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else if (streq(name, "shared"))
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*ret = MS_SHARED;
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else if (streq(name, "slave"))
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*ret = MS_SLAVE;
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else if (streq(name, "private"))
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*ret = MS_PRIVATE;
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else
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return -EINVAL;
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return 0;
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}
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