diff --git a/manual/filesys.texi b/manual/filesys.texi
index 73e630842e..5ee4291867 100644
--- a/manual/filesys.texi
+++ b/manual/filesys.texi
@@ -15,6 +15,7 @@ access permissions and modification times.
 @menu
 * Working Directory::           This is used to resolve relative
 				 file names.
+* Descriptor-Relative Access::  Ways to control pathname lookup.
 * Accessing Directories::       Finding out what files a directory
 				 contains.
 * Working with Directory Trees:: Apply actions to all files or a selectable
@@ -206,6 +207,110 @@ An I/O error occurred.
 @end table
 @end deftypefun
 
+@node Descriptor-Relative Access
+@section Descriptor-Relative Access
+@cindex pathname resolution based on descriptors
+@cindex descriptor-based pathname resolution
+@cindex @code{@dots{}at} functions
+
+Many functions that accept pathnames have variants have @code{@dots{}at}
+variants which accept a file descriptor and pathname argument instead of
+just a pathname argument.  For example, @code{fstatat} is the
+descriptor-based variant of the @code{fstat} function.  Most of such
+functions also accept an additional flags argument which changes the
+behavior of the pathname lookup based on the @code{AT_@dots{}} flags
+specified.
+
+The file descriptor used by these @code{@dots{}at} functions has the
+following uses:
+
+@itemize @bullet
+@item
+It can be a file descriptor referring to a directory.  Such a descriptor
+can be created explicitly using the @code{open} function, with or
+without the @code{O_DIRECTORY} flag.  @xref{Opening and Closing Files}.
+Or it can be created implicity by @code{opendir} and retrieved using the
+@code{dirfd} function.  @xref{Opening a Directory}.
+
+If a directory descriptor is used with one of the @code{@dots{}at}
+functions, a relative pathname argument is resolved relatively to that
+directory, just as if the directory were the current working directory.
+Absolute pathname arguments (starting with @samp{/}) are resolved
+against the file system root, and the descriptor argument is effectively
+ignored for the purposes of pathname lookup.
+
+This means that pathname lookup is not constrained to the directory of
+the descriptor.  For example, it is possible to access a file
+@file{example} in the parent directory using a pathname argument
+@code{"../example"}, or in the root directory using @code{"/example"}.
+
+@item
+@vindex @code{AT_FDCWD}
+The special value @code{AT_FDCWD}.  This means that the current working
+directory is used for the lookup if the pathname is a relative.  For
+@code{@dots{}at} functions with an @code{AT_@dots{}} flags argument,
+this provides a shortcut to use those flags with regular (not
+descriptor-based) pathname lookups.
+
+@item
+An arbitrary file descriptor, along with an empty string @code{""} as
+the pathname argument, and the @code{AT_EMPTY_PATH} flag.  In this case,
+the operation uses the file descriptor directly, without further
+pathname resolution.  On Linux, this allows operations on descriptors
+opened with the @code{O_PATH} flag.  For regular descriptors (without
+@code{O_PATH}), the same functionality is also available through the
+plain descriptor-based functions (for example, @code{fstat} instead of
+@code{fstatat}).
+
+This is a GNU extension.
+@end itemize
+
+@cindex pathname resolution flags
+@cindex @code{AT_*} pathname resolution flags
+The flags argument in @code{@dots{}at} functions can be a combination of
+the following flags, defined in @file{fcntl.h}.  Not all such functions
+support all flags, and some (such as @code{openat}) do not accept a
+flags argument at all.
+
+In the flag descriptions below, the @dfn{effective final pathname
+component} refers to the final component (basename) of the full path
+constructed from the descriptor and pathname arguments, using pathname
+lookup, as described above.
+
+@vtable @code
+@item AT_EMPTY_PATH
+This flag is used with an empty pathname @code{""} and a descriptor
+which does not necessarily refer to a directory.  It is most useful with
+@code{O_PATH} descriptors, as described above.  This flag is a GNU
+extension.
+
+@item AT_NO_AUTOMOUNT
+If the effective final pathname component refers to a potential file
+system mount point controlled by an auto-mounting service, the operation
+does not trigger auto-mounting and refers to the unmounted mount point
+instead.  @xref{Mount-Unmount-Remount}.  If a file system has already
+been mounted at the effective final pathname component, the operation
+applies to the mounted file system, not the underlying file system that
+was mounted over.  This flag is a GNU extension.
+
+@item AT_SYMLINK_FOLLOW
+If the effective final pathname component is a symbolic link, the
+operation follows the symbolic link and operates on its target.  (For
+most functions, this is the default behavior.)
+
+@item AT_SYMLINK_NOFOLLOW
+If the effective final pathname component is a symbolic link, the
+operation operates on the symbolic link, without following it.  The
+difference in behavior enabled by this flag is similar to the difference
+between the @code{lstat} and @code{stat} functions, or the behavior
+activated by the @code{O_NOFOLLOW} argument to the @code{open} function.
+Even with the @code{AT_SYMLINK_NOFOLLOW} flag present, symbolic links in
+a non-final position of the pathname are still followed.
+@end vtable
+
+There is no relationship between these flags and the type argument to
+the @code{getauxval} function (with @code{AT_@dots{}} constants defined
+in @file{elf.h}).
 
 @node Accessing Directories
 @section Accessing Directories
@@ -1250,10 +1355,11 @@ A hardware error occurred while trying to read or write the to filesystem.
 
 The @code{linkat} function is analogous to the @code{link} function,
 except that it identifies its source and target using a combination of a
-file descriptor (referring to a directory) and a pathname.  If a
-pathnames is not absolute, it is resolved relative to the corresponding
-file descriptor.  The special file descriptor @code{AT_FDCWD} denotes
-the current directory.
+file descriptor (referring to a directory) and a pathname.
+@xref{Descriptor-Relative Access}.  For @code{linkat}, if a pathname is
+not absolute, it is resolved relative to the corresponding file
+descriptor.  As usual, the special file descriptor @code{AT_FDCWD}
+denotes the current directory.
 
 The @var{flags} argument is a combination of the following flags:
 
@@ -2091,9 +2197,36 @@ function is available under the name @code{fstat} and so transparently
 replaces the interface for small files on 32-bit machines.
 @end deftypefun
 
-@c fstatat will call alloca and snprintf if the syscall is not
-@c available.
-@c @safety{@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}}
+@deftypefun int fstatat (int @var{filedes}, const char *@var{filename}, struct stat *@var{buf}, int @var{flags})
+@standards{POSIX.1, sys/stat.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function is a descriptor-relative version of the @code{fstat}
+function above.  @xref{Descriptor-Relative Access}.  The @var{flags}
+argument can contain a combination of the flags @code{AT_EMPTY_PATH},
+@code{AT_NO_AUTOMOUNT}, @code{AT_SYMLINK_NOFOLLOW}.
+
+Compared to @code{fstat}, the following additional error conditions can
+occur:
+
+@table @code
+@item EBADF
+The @var{filedes} argument is not a valid file descriptor.
+
+@item EINVAL
+The @var{flags} argument is not valid for this function.
+
+@item ENOTDIR
+The descriptor @var{filedes} is not associated with a directory, and
+@var{filename} is a relative pathname.
+@end table
+@end deftypefun
+
+@deftypefun int fstatat64 (int @var{filedes}, const char *@var{filename}, struct stat64 *@var{buf}, int @var{flags})
+@standards{GNU, sys/stat.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+This function is the large-file variant of @code{fstatat}, similar to
+how @code{fstat64} is the variant of @code{fstat}.
+@end deftypefun
 
 @deftypefun int lstat (const char *@var{filename}, struct stat *@var{buf})
 @standards{BSD, sys/stat.h}
@@ -3582,12 +3715,10 @@ The @code{mkdtemp} function comes from OpenBSD.
 @c fchmodat
 @c fchownat
 @c futimesat
-@c fstatat (there's a commented-out safety assessment for this one)
 @c statx
 @c mkdirat
 @c mkfifoat
 @c name_to_handle_at
-@c openat
 @c open_by_handle_at
 @c readlinkat
 @c renameat
diff --git a/manual/llio.texi b/manual/llio.texi
index fe59002915..48fe2dc862 100644
--- a/manual/llio.texi
+++ b/manual/llio.texi
@@ -180,6 +180,34 @@ new, extended API using 64 bit file sizes and offsets transparently
 replaces the old API.
 @end deftypefun
 
+@deftypefun int openat (int @var{filedes}, const char *@var{filename}, int @var{flags}[, mode_t @var{mode}])
+@standards{POSIX.1, fcntl.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
+This function is the descriptor-relative variant of the @code{open}
+function.  @xref{Descriptor-Relative Access}.
+
+Note that the @var{flags} argument of @code{openat} does not accept
+@code{AT_@dots{}} flags, only the flags described for the @code{open}
+function above.
+
+The @code{openat} function can fail for additional reasons:
+
+@table @code
+@item EBADF
+The @var{filedes} argument is not a valid file descriptor.
+
+@item ENOTDIR
+The descriptor @var{filedes} is not associated with a directory, and
+@var{filename} is a relative pathname.
+@end table
+@end deftypefun
+
+@deftypefun int openat (int @var{filedes}, const char *@var{filename}, int @var{flags}[, mode_t @var{mode}])
+@standards{GNU, fcntl.h}
+The large-file variant of the @code{openat}, similar to how
+@code{open64} is the large-file variant of @code{open}.
+@end deftypefun
+
 @deftypefn {Obsolete function} int creat (const char *@var{filename}, mode_t @var{mode})
 @standards{POSIX.1, fcntl.h}
 @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
diff --git a/manual/startup.texi b/manual/startup.texi
index 21c48cd037..b2577cc0c4 100644
--- a/manual/startup.texi
+++ b/manual/startup.texi
@@ -664,9 +664,10 @@ basis there may be information that is not available any other way.
 @c Reads from hwcap or iterates over constant auxv.
 This function is used to inquire about the entries in the auxiliary
 vector.  The @var{type} argument should be one of the @samp{AT_} symbols
-defined in @file{elf.h}.  If a matching entry is found, the value is
-returned; if the entry is not found, zero is returned and @code{errno} is
-set to @code{ENOENT}.
+defined in @file{elf.h}.  (There is no relationship between these types
+and the pathname lookup flags in @file{fcntl.h}.)  If a matching entry
+is found, the value is returned; if the entry is not found, zero is
+returned and @code{errno} is set to @code{ENOENT}.
 @end deftypefun
 
 For some platforms, the key @code{AT_HWCAP} is the easiest way to inquire
