2020-03-30 06:34:45 +00:00
|
|
|
.\" Copyright (C) 2019 Aleksa Sarai <cyphar@cyphar.com>
|
|
|
|
.\"
|
|
|
|
.\" %%%LICENSE_START(VERBATIM)
|
|
|
|
.\" Permission is granted to make and distribute verbatim copies of this
|
|
|
|
.\" manual provided the copyright notice and this permission notice are
|
|
|
|
.\" preserved on all copies.
|
|
|
|
.\"
|
|
|
|
.\" Permission is granted to copy and distribute modified versions of this
|
|
|
|
.\" manual under the conditions for verbatim copying, provided that the
|
|
|
|
.\" entire resulting derived work is distributed under the terms of a
|
|
|
|
.\" permission notice identical to this one.
|
|
|
|
.\"
|
|
|
|
.\" Since the Linux kernel and libraries are constantly changing, this
|
|
|
|
.\" manual page may be incorrect or out-of-date. The author(s) assume no
|
|
|
|
.\" responsibility for errors or omissions, or for damages resulting from
|
|
|
|
.\" the use of the information contained herein. The author(s) may not
|
|
|
|
.\" have taken the same level of care in the production of this manual,
|
|
|
|
.\" which is licensed free of charge, as they might when working
|
|
|
|
.\" professionally.
|
|
|
|
.\"
|
|
|
|
.\" Formatted or processed versions of this manual, if unaccompanied by
|
|
|
|
.\" the source, must acknowledge the copyright and authors of this work.
|
|
|
|
.\" %%%LICENSE_END
|
getent.1, ldd.1, locale.1, localedef.1, memusage.1, memusagestat.1, mtrace.1, _exit.2, _syscall.2, accept.2, access.2, acct.2, add_key.2, adjtimex.2, alloc_hugepages.2, arch_prctl.2, bdflush.2, bind.2, bpf.2, brk.2, cacheflush.2, capget.2, chdir.2, chmod.2, chown.2, chroot.2, clock_getres.2, clock_nanosleep.2, clone.2, close.2, close_range.2, connect.2, copy_file_range.2, create_module.2, delete_module.2, dup.2, epoll_create.2, epoll_ctl.2, epoll_wait.2, eventfd.2, execve.2, execveat.2, fanotify_init.2, fanotify_mark.2, fcntl.2, flock.2, fork.2, fsync.2, futex.2, get_kernel_syms.2, get_mempolicy.2, get_robust_list.2, getcpu.2, getdents.2, getdomainname.2, getgid.2, getgroups.2, gethostname.2, getitimer.2, getpagesize.2, getpeername.2, getpid.2, getpriority.2, getrandom.2, getresuid.2, getrlimit.2, getrusage.2, getsid.2, getsockname.2, getsockopt.2, gettid.2, gettimeofday.2, getuid.2, getunwind.2, getxattr.2, idle.2, init_module.2, inotify_add_watch.2, inotify_rm_watch.2, io_cancel.2, io_destroy.2, io_getevents.2, io_setup.2, io_submit.2, ioctl.2, ioctl_console.2, ioctl_fat.2, ioctl_ficlonerange.2, ioctl_fideduperange.2, ioctl_fslabel.2, ioctl_getfsmap.2, ioctl_ns.2, ioctl_tty.2, ioctl_userfaultfd.2, ioperm.2, iopl.2, ipc.2, kcmp.2, kexec_load.2, keyctl.2, kill.2, link.2, listen.2, listxattr.2, llseek.2, lookup_dcookie.2, lseek.2, madvise.2, mbind.2, membarrier.2, memfd_create.2, migrate_pages.2, mincore.2, mkdir.2, mknod.2, mlock.2, mmap.2, mmap2.2, modify_ldt.2, mount.2, move_pages.2, mprotect.2, mq_getsetattr.2, mremap.2, msgctl.2, msgget.2, msgop.2, msync.2, nanosleep.2, nfsservctl.2, nice.2, open.2, open_by_handle_at.2, openat2.2, pause.2, pciconfig_read.2, perf_event_open.2, perfmonctl.2, personality.2, pidfd_getfd.2, pidfd_open.2, pidfd_send_signal.2, pipe.2, pivot_root.2, pkey_alloc.2, poll.2, posix_fadvise.2, prctl.2, pread.2, process_vm_readv.2, ptrace.2, query_module.2, quotactl.2, read.2, readahead.2, readdir.2, readlink.2, readv.2, reboot.2, recv.2, remap_file_pages.2, removexattr.2, rename.2, request_key.2, restart_syscall.2, rmdir.2, rt_sigqueueinfo.2, s390_guarded_storage.2, s390_pci_mmio_write.2, s390_runtime_instr.2, s390_sthyi.2, sched_get_priority_max.2, sched_rr_get_interval.2, sched_setaffinity.2, sched_setattr.2, sched_setparam.2, sched_setscheduler.2, sched_yield.2, seccomp.2, select.2, select_tut.2, semctl.2, semget.2, semop.2, send.2, sendfile.2, set_thread_area.2, seteuid.2, setfsgid.2, setfsuid.2, setgid.2, setpgid.2, setresuid.2, setreuid.2, setsid.2, setuid.2, setup.2, setxattr.2, sgetmask.2, shmctl.2, shmget.2, shmop.2, shutdown.2, sigaction.2, sigaltstack.2, signal.2, signalfd.2, sigpending.2, sigprocmask.2, sigreturn.2, sigsuspend.2, sigwaitinfo.2, socket.2, socketcall.2, socketpair.2, splice.2, spu_create.2, spu_run.2, stat.2, statfs.2, statx.2, stime.2, subpage_prot.2, swapon.2, symlink.2, sync.2, sync_file_range.2, syscall.2, syscalls.2, sysctl.2, sysfs.2, sysinfo.2, syslog.2, time.2, timer_create.2, timer_delete.2, timer_getoverrun.2, timer_settime.2, timerfd_create.2, times.2, tkill.2, truncate.2, umask.2, umount.2, uname.2, unimplemented.2, unlink.2, unshare.2, uselib.2, userfaultfd.2, ustat.2, utime.2, utimensat.2, vfork.2, vhangup.2, vm86.2, vmsplice.2, wait.2, wait4.2, write.2, CPU_SET.3, __ppc_get_timebase.3, __ppc_set_ppr_med.3, __ppc_yield.3, __setfpucw.3, a64l.3, abort.3, abs.3, acos.3, acosh.3, addseverity.3, adjtime.3, aio_cancel.3, aio_error.3, aio_fsync.3, aio_read.3, aio_return.3, aio_suspend.3, aio_write.3, alloca.3, argz_add.3, asin.3, asinh.3, asprintf.3, assert.3, assert_perror.3, atan.3, atan2.3, atanh.3, atexit.3, atof.3, atoi.3, backtrace.3, basename.3, bcmp.3, bcopy.3, bindresvport.3, bsd_signal.3, bsearch.3, bstring.3, btowc.3, byteorder.3, bzero.3, cabs.3, cacos.3, cacosh.3, canonicalize_file_name.3, carg.3, casin.3, casinh.3, catan.3, catanh.3, catgets.3, catopen.3, cbrt.3, ccos.3, ccosh.3, ceil.3, cexp.3, cexp2.3, cfree.3, cimag.3, circleq.3, clearenv.3, clock.3, clock_getcpuclockid.3, clog.3, clog10.3, clog2.3, closedir.3, cmsg.3, confstr.3, conj.3, copysign.3, cos.3, cosh.3, cpow.3, cproj.3, creal.3, crypt.3, csin.3, csinh.3, csqrt.3, ctan.3, ctanh.3, ctermid.3, ctime.3, daemon.3, des_crypt.3, difftime.3, dirfd.3, div.3, dl_iterate_phdr.3, dladdr.3, dlerror.3, dlinfo.3, dlopen.3, dlsym.3, drand48.3, drand48_r.3, duplocale.3, dysize.3, ecvt.3, ecvt_r.3, encrypt.3, endian.3, envz_add.3, erf.3, erfc.3, err.3, errno.3, error.3, ether_aton.3, euidaccess.3, exec.3, exit.3, exp.3, exp10.3, exp2.3, expm1.3, fabs.3, fclose.3, fcloseall.3, fdim.3, fenv.3, ferror.3, fexecve.3, fflush.3, ffs.3, fgetc.3, fgetgrent.3, fgetpwent.3, fgetwc.3, fgetws.3, fileno.3, finite.3, flockfile.3, floor.3, fma.3, fmax.3, fmemopen.3, fmin.3, fmod.3, fmtmsg.3, fnmatch.3, fopen.3, fopencookie.3, fpathconf.3, fpclassify.3, fpurge.3, fputwc.3, fputws.3, fread.3, frexp.3, fseek.3, fseeko.3, ftime.3, ftok.3, fts.3, ftw.3, futimes.3, fwide.3, gamma.3, gcvt.3, get_nprocs_conf.3, get_phys_pages.3, getaddrinfo.3, getaddrinfo_a.3, getauxval.3, getcontext.3, getcwd.3, getdate.3, getdirentries.3, getdtablesize.3, getentropy.3, getenv.3, getfsent.3, getgrent.3, getgrent_r.3, getgrnam.3, getgrouplist.3, gethostbyname.3, gethostid.3, getifaddrs.3, getipnodebyname.3, getline.3, getloadavg.3, getlogin.3, getmntent.3, getnameinfo.3, getnetent.3, getnetent_r.3, getopt.3, getpass.3, getprotoent.3, getprotoent_r.3, getpt.3, getpw.3, getpwent.3, getpwent_r.3, getpwnam.3, getrpcent.3, getrpcent_r.3, getrpcport.3, gets.3, getservent.3, getservent_r.3, getspnam.3, getsubopt.3, getttyent.3, getumask.3, getusershell.3, getutent.3, getutmp.3, getw.3, getwchar.3, glob.3, gnu_get_libc_version.3, grantpt.3, group_member.3, gsignal.3, hsearch.3, hypot.3, iconv.3, iconv_close.3, iconv_open.3, if_nameindex.3, if_nametoindex.3, ilogb.3, index.3, inet.3, inet_net_pton.3, inet_ntop.3, inet_pton.3, initgroups.3, insque.3, isalpha.3, isatty.3, isfdtype.3, isgreater.3, iswalnum.3, iswalpha.3, iswblank.3, iswcntrl.3, iswctype.3, iswdigit.3, iswgraph.3, iswlower.3, iswprint.3, iswpunct.3, iswspace.3, iswupper.3, iswxdigit.3, j0.3, key_setsecret.3, killpg.3, ldexp.3, lgamma.3, lio_listio.3, list.3, localeconv.3, lockf.3, log.3, log10.3, log1p.3, log2.3, logb.3, login.3, lrint.3, lround.3, lsearch.3, lseek64.3, makecontext.3, makedev.3, mallinfo.3, malloc.3, malloc_get_state.3, malloc_hook.3, malloc_info.3, malloc_stats.3, malloc_trim.3, malloc_usable_size.3, mallopt.3, matherr.3, mblen.3, mbrlen.3, mbrtowc.3, mbsinit.3, mbsnrtowcs.3, mbsrtowcs.3, mbstowcs.3, mbtowc.3, mcheck.3, memccpy.3, memchr.3, memcmp.3, memcpy.3, memfrob.3, memmem.3, memmove.3, mempcpy.3, memset.3, mkdtemp.3, mkfifo.3, mkstemp.3, mktemp.3, modf.3, mpool.3, mq_close.3, mq_getattr.3, mq_notify.3, mq_open.3, mq_receive.3, mq_send.3, mq_unlink.3, mtrace.3, nan.3, newlocale.3, nextafter.3, nextup.3, nl_langinfo.3, ntp_gettime.3, on_exit.3, open_memstream.3, opendir.3, openpty.3, perror.3, popen.3, posix_fallocate.3, posix_madvise.3, posix_memalign.3, posix_openpt.3, posix_spawn.3, pow.3, pow10.3, printf.3, profil.3, psignal.3, pthread_attr_init.3, pthread_attr_setaffinity_np.3, pthread_attr_setdetachstate.3, pthread_attr_setguardsize.3, pthread_attr_setinheritsched.3, pthread_attr_setschedparam.3, pthread_attr_setschedpolicy.3, pthread_attr_setscope.3, pthread_attr_setsigmask_np.3, pthread_attr_setstack.3, pthread_attr_setstackaddr.3, pthread_attr_setstacksize.3, pthread_cancel.3, pthread_cleanup_push.3, pthread_cleanup_push_defer_np.3, pthread_create.3, pthread_detach.3, pthread_equal.3, pthread_exit.3, pthread_getattr_default_np.3, pthread_getattr_np.3, pthread_getcpuclockid.3, pthread_join.3, pthread_kill.3, pthread_kill_other_threads_np.3, pthread_mutex_consistent.3, pthread_mutexattr_getpshared.3, pthread_mutexattr_setrobust.3, pthread_rwlockattr_setkind_np.3, pthread_self.3, pthread_setaffinity_np.3, pthread_setcancelstate.3, pthread_setconcurrency.3, pthread_setname_np.3, pthread_setschedparam.3, pthread_setschedprio.3, pthread_sigmask.3, pthread_sigqueue.3, pthread_spin_init.3, pthread_spin_lock.3, pthread_testcancel.3, pthread_tryjoin_np.3, pthread_yield.3, ptsname.3, putenv.3, putgrent.3, putpwent.3, puts.3, putwchar.3, qecvt.3, qsort.3, raise.3, rand.3, random.3, random_r.3, rcmd.3, re_comp.3, readdir.3, readdir_r.3, realpath.3, regex.3, remainder.3, remove.3, remquo.3, resolver.3, rewinddir.3, rexec.3, rint.3, round.3, rpc.3, rpmatch.3, rtime.3, rtnetlink.3, scalb.3, scalbln.3, scandir.3, scanf.3, sched_getcpu.3, seekdir.3, sem_close.3, sem_destroy.3, sem_getvalue.3, sem_init.3, sem_open.3, sem_post.3, sem_unlink.3, sem_wait.3, setaliasent.3, setbuf.3, setenv.3, setjmp.3, setlocale.3, setlogmask.3, setnetgrent.3, shm_open.3, siginterrupt.3, signbit.3, significand.3, sigpause.3, sigqueue.3, sigset.3, sigsetops.3, sigvec.3, sigwait.3, sin.3, sincos.3, sinh.3, sleep.3, slist.3, sockatmark.3, sqrt.3, stailq.3, statvfs.3, stdarg.3, stdio.3, stdio_ext.3, stpcpy.3, stpncpy.3, strcasecmp.3, strcat.3, strchr.3, strcmp.3, strcoll.3, strcpy.3, strdup.3, strerror.3, strfmon.3, strfromd.3, strfry.3, strftime.3, string.3, strlen.3, strnlen.3, strpbrk.3, strptime.3, strsep.3, strsignal.3, strspn.3, strstr.3, strtod.3, strtoimax.3, strtok.3, strtol.3, strtoul.3, strverscmp.3, strxfrm.3, swab.3, sysconf.3, syslog.3, system.3, sysv_signal.3, tailq.3, tan.3, tanh.3, tcgetpgrp.3, tcgetsid.3, telldir.3, tempnam.3, termios.3, tgamma.3, timegm.3, timeradd.3, tmpfile.3, tmpnam.3, toascii.3, toupper.3, towctrans.3, towlower.3, towupper.3, trunc.3, tsearch.3, ttyname.3, ttyslot.3, tzset.3, ualarm.3, ulimit.3, undocumented.3, ungetwc.3, unlocked_stdio.3, unlockpt.3, updwtmp.3, uselocale.3, usleep.3, wcpcpy.3, wcpncpy.3, wcrtomb.3, wcscasecmp.3, wcscat.3, wcschr.3, wcscmp.3, wcscpy.3, wcscspn.3, wcsdup.3, wcslen.3, wcsncasecmp.3, wcsncat.3, wcsncmp.3, wcsncpy.3, wcsnlen.3, wcsnrtombs.3, wcspbrk.3, wcsrchr.3, wcsrtombs.3, wcsspn.3, wcsstr.3, wcstoimax.3, wcstok.3, wcstombs.3, wcswidth.3, wctob.3, wctomb.3, wctrans.3, wctype.3, wcwidth.3, wmemchr.3, wmemcmp.3, wmemcpy.3, wmemmove.3, wmemset.3, wordexp.3, wprintf.3, xcrypt.3, xdr.3, y0.3, cciss.4, console_codes.4, dsp56k.4, hpsa.4, initrd.4, loop.4, lp.4, msr.4, random.4, rtc.4, smartpqi.4, veth.4, wavelan.4, acct.5, core.5, elf.5, hosts.5, locale.5, proc.5, resolv.conf.5, rpc.5, slabinfo.5, sysfs.5, tmpfs.5, utmp.5, address_families.7, aio.7, attributes.7, bootparam.7, capabilities.7, cgroups.7, complex.7, ddp.7, environ.7, epoll.7, fanotify.7, feature_test_macros.7, hier.7, inode.7, inotify.7, ip.7, ipv6.7, keyrings.7, locale.7, man-pages.7, man.7, math_error.7, mount_namespaces.7, namespaces.7, netdevice.7, netlink.7, numa.7, packet.7, pkeys.7, pthreads.7, queue.7, raw.7, rtnetlink.7, sched.7, session-keyring.7, shm_overview.7, sigevent.7, signal-safety.7, signal.7, sock_diag.7, socket.7, spufs.7, symlink.7, system_data_types.7, tcp.7, time_namespaces.7, udp.7, udplite.7, unicode.7, unix.7, uri.7, user_namespaces.7, vdso.7, vsock.7, x25.7, iconvconfig.8, ld.so.8, ldconfig.8, sln.8, tzselect.8: tstamp
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2021-03-21 23:15:34 +00:00
|
|
|
.TH OPENAT2 2 2021-03-22 "Linux" "Linux Programmer's Manual"
|
2020-03-30 06:34:45 +00:00
|
|
|
.SH NAME
|
|
|
|
openat2 \- open and possibly create a file (extended)
|
|
|
|
.SH SYNOPSIS
|
|
|
|
.nf
|
2021-05-10 17:55:36 +00:00
|
|
|
.BR "#include <fcntl.h>" \
|
|
|
|
" /* Definition of " O_* " and " S_* " constants */"
|
|
|
|
.BR "#include <linux/openat2.h>" " /* Definition of " RESOLVE_* " constants */"
|
|
|
|
.BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */"
|
|
|
|
.B #include <unistd.h>
|
2020-03-30 06:34:45 +00:00
|
|
|
.PP
|
2021-05-10 17:55:36 +00:00
|
|
|
.BI "long syscall(SYS_openat2, int " dirfd ", const char *" pathname ,
|
|
|
|
.BI " struct open_how *" how ", size_t " size );
|
2020-03-30 06:34:45 +00:00
|
|
|
.fi
|
|
|
|
.PP
|
|
|
|
.IR Note :
|
2021-05-10 17:55:36 +00:00
|
|
|
glibc provides no wrapper for
|
|
|
|
.BR openat2 (),
|
|
|
|
necessitating the use of
|
|
|
|
.BR syscall (2).
|
2020-03-30 06:34:45 +00:00
|
|
|
.SH DESCRIPTION
|
|
|
|
The
|
|
|
|
.BR openat2 ()
|
2020-03-30 11:43:32 +00:00
|
|
|
system call is an extension of
|
|
|
|
.BR openat (2)
|
|
|
|
and provides a superset of its functionality.
|
|
|
|
.PP
|
|
|
|
The
|
|
|
|
.BR openat2 ()
|
2020-03-30 06:34:45 +00:00
|
|
|
system call opens the file specified by
|
|
|
|
.IR pathname .
|
|
|
|
If the specified file does not exist, it may optionally (if
|
|
|
|
.B O_CREAT
|
|
|
|
is specified in
|
|
|
|
.IR how.flags )
|
2020-03-30 10:28:41 +00:00
|
|
|
be created.
|
2020-03-30 06:34:45 +00:00
|
|
|
.PP
|
|
|
|
As with
|
|
|
|
.BR openat (2),
|
|
|
|
if
|
|
|
|
.I pathname
|
2020-03-30 10:28:41 +00:00
|
|
|
is a relative pathname, then it is interpreted relative to the
|
2020-03-30 06:34:45 +00:00
|
|
|
directory referred to by the file descriptor
|
|
|
|
.I dirfd
|
|
|
|
(or the current working directory of the calling process, if
|
|
|
|
.I dirfd
|
|
|
|
is the special value
|
2020-03-30 10:28:41 +00:00
|
|
|
.BR AT_FDCWD ).
|
2020-03-30 06:34:45 +00:00
|
|
|
If
|
|
|
|
.I pathname
|
2020-03-30 10:28:41 +00:00
|
|
|
is an absolute pathname, then
|
2020-03-30 06:34:45 +00:00
|
|
|
.I dirfd
|
|
|
|
is ignored (unless
|
|
|
|
.I how.resolve
|
|
|
|
contains
|
2020-06-12 19:54:55 +00:00
|
|
|
.BR RESOLVE_IN_ROOT ,
|
2020-03-30 06:34:45 +00:00
|
|
|
in which case
|
|
|
|
.I pathname
|
|
|
|
is resolved relative to
|
2020-03-30 10:28:41 +00:00
|
|
|
.IR dirfd ).
|
2020-03-30 06:34:45 +00:00
|
|
|
.PP
|
|
|
|
Rather than taking a single
|
2020-03-30 06:53:59 +00:00
|
|
|
.I flags
|
2020-03-30 10:28:41 +00:00
|
|
|
argument, an extensible structure (\fIhow\fP) is passed to allow for
|
2020-03-30 06:34:45 +00:00
|
|
|
future extensions.
|
2020-03-30 10:28:41 +00:00
|
|
|
The
|
2020-03-30 06:34:45 +00:00
|
|
|
.I size
|
2020-03-30 10:28:41 +00:00
|
|
|
argument must be specified as
|
|
|
|
.IR "sizeof(struct open_how)" .
|
2020-03-30 06:51:21 +00:00
|
|
|
.\"
|
2020-03-30 06:34:45 +00:00
|
|
|
.SS The open_how structure
|
2020-03-30 11:43:32 +00:00
|
|
|
The
|
|
|
|
.I how
|
|
|
|
argument specifies how
|
2020-03-30 06:34:45 +00:00
|
|
|
.I pathname
|
|
|
|
should be opened, and acts as a superset of the
|
2020-03-30 12:49:20 +00:00
|
|
|
.IR flags
|
|
|
|
and
|
|
|
|
.IR mode
|
2020-03-30 06:34:45 +00:00
|
|
|
arguments to
|
|
|
|
.BR openat (2).
|
2020-03-30 11:43:32 +00:00
|
|
|
This argument is a pointer to a structure of the following form:
|
2020-03-30 06:34:45 +00:00
|
|
|
.PP
|
|
|
|
.in +4n
|
|
|
|
.EX
|
|
|
|
struct open_how {
|
2020-03-30 07:54:06 +00:00
|
|
|
u64 flags; /* O_* flags */
|
|
|
|
u64 mode; /* Mode for O_{CREAT,TMPFILE} */
|
|
|
|
u64 resolve; /* RESOLVE_* flags */
|
2020-03-30 06:34:45 +00:00
|
|
|
/* ... */
|
|
|
|
};
|
|
|
|
.EE
|
|
|
|
.in
|
|
|
|
.PP
|
|
|
|
Any future extensions to
|
|
|
|
.BR openat2 ()
|
2020-03-30 10:28:41 +00:00
|
|
|
will be implemented as new fields appended to the above structure,
|
|
|
|
with a zero value in a new field resulting in the kernel behaving
|
|
|
|
as though that extension field was not present.
|
2020-03-30 20:19:36 +00:00
|
|
|
Therefore, the caller
|
|
|
|
.I must
|
|
|
|
zero-fill this structure on
|
2020-03-30 10:28:41 +00:00
|
|
|
initialization.
|
|
|
|
(See the "Extensibility" section of the
|
2020-03-30 06:34:45 +00:00
|
|
|
.B NOTES
|
|
|
|
for more detail on why this is necessary.)
|
|
|
|
.PP
|
2020-03-30 10:28:41 +00:00
|
|
|
The fields of the
|
|
|
|
.I open_how
|
|
|
|
structure are as follows:
|
2020-03-30 07:37:03 +00:00
|
|
|
.TP
|
2020-03-30 06:34:45 +00:00
|
|
|
.I flags
|
2020-03-30 10:28:41 +00:00
|
|
|
This field specifies
|
|
|
|
the file creation and file status flags to use when opening the file.
|
2020-03-30 06:34:45 +00:00
|
|
|
All of the
|
|
|
|
.B O_*
|
|
|
|
flags defined for
|
|
|
|
.BR openat (2)
|
|
|
|
are valid
|
|
|
|
.BR openat2 ()
|
|
|
|
flag values.
|
2020-03-30 07:37:03 +00:00
|
|
|
.IP
|
2020-03-30 10:28:41 +00:00
|
|
|
Whereas
|
|
|
|
.BR openat (2)
|
|
|
|
ignores unknown bits in its
|
|
|
|
.I flags
|
|
|
|
argument,
|
2020-03-30 06:34:45 +00:00
|
|
|
.BR openat2 ()
|
2020-03-30 10:28:41 +00:00
|
|
|
returns an error if unknown or conflicting flags are specified in
|
2020-03-30 09:48:03 +00:00
|
|
|
.IR how.flags .
|
2020-03-30 07:37:03 +00:00
|
|
|
.TP
|
|
|
|
.I mode
|
2020-03-30 10:28:41 +00:00
|
|
|
This field specifies the
|
|
|
|
mode for the new file, with identical semantics to the
|
2020-03-30 06:34:45 +00:00
|
|
|
.I mode
|
2020-03-30 10:28:41 +00:00
|
|
|
argument of
|
2020-03-30 06:34:45 +00:00
|
|
|
.BR openat (2).
|
2020-03-30 07:37:03 +00:00
|
|
|
.IP
|
2020-03-30 10:28:41 +00:00
|
|
|
Whereas
|
|
|
|
.BR openat (2)
|
|
|
|
ignores bits other than those in the range
|
|
|
|
.I 07777
|
|
|
|
in its
|
|
|
|
.I mode
|
|
|
|
argument,
|
2020-03-30 06:34:45 +00:00
|
|
|
.BR openat2 ()
|
2020-03-30 10:28:41 +00:00
|
|
|
returns an error if
|
2020-03-30 09:48:03 +00:00
|
|
|
.I how.mode
|
2020-03-30 10:28:41 +00:00
|
|
|
contains bits other than
|
|
|
|
.IR 07777 .
|
|
|
|
Similarly, an error is returned if
|
2020-03-30 06:34:45 +00:00
|
|
|
.BR openat2 ()
|
2020-10-22 20:43:25 +00:00
|
|
|
is called with a nonzero
|
2020-03-30 12:49:20 +00:00
|
|
|
.IR how.mode
|
|
|
|
and
|
|
|
|
.IR how.flags
|
2020-03-30 06:34:45 +00:00
|
|
|
does not contain
|
2020-03-30 12:49:20 +00:00
|
|
|
.BR O_CREAT
|
|
|
|
or
|
|
|
|
.BR O_TMPFILE .
|
2020-03-30 07:37:03 +00:00
|
|
|
.TP
|
2020-03-30 06:34:45 +00:00
|
|
|
.I resolve
|
2020-03-30 10:28:41 +00:00
|
|
|
This is a bit-mask of flags that modify the way in which
|
2020-03-30 06:34:45 +00:00
|
|
|
.B all
|
|
|
|
components of
|
|
|
|
.I pathname
|
2020-03-30 10:28:41 +00:00
|
|
|
will be resolved.
|
|
|
|
(See
|
2020-03-30 06:34:45 +00:00
|
|
|
.BR path_resolution (7)
|
|
|
|
for background information.)
|
2020-03-30 10:28:41 +00:00
|
|
|
.IP
|
2020-03-30 06:34:45 +00:00
|
|
|
The primary use case for these flags is to allow trusted programs to restrict
|
|
|
|
how untrusted paths (or paths inside untrusted directories) are resolved.
|
|
|
|
The full list of
|
|
|
|
.I resolve
|
2020-03-30 10:28:41 +00:00
|
|
|
flags is as follows:
|
2020-03-30 07:37:03 +00:00
|
|
|
.RS
|
2020-03-30 06:34:45 +00:00
|
|
|
.TP
|
|
|
|
.B RESOLVE_BENEATH
|
2020-03-31 07:39:22 +00:00
|
|
|
.\" commit adb21d2b526f7f196b2f3fdca97d80ba05dd14a0
|
2020-03-30 06:34:45 +00:00
|
|
|
Do not permit the path resolution to succeed if any component of the resolution
|
|
|
|
is not a descendant of the directory indicated by
|
|
|
|
.IR dirfd .
|
2020-03-30 10:28:41 +00:00
|
|
|
This causes absolute symbolic links (and absolute values of
|
2020-03-30 06:34:45 +00:00
|
|
|
.IR pathname )
|
|
|
|
to be rejected.
|
2020-03-30 07:37:03 +00:00
|
|
|
.IP
|
2020-03-31 07:11:20 +00:00
|
|
|
Currently, this flag also disables magic-link resolution (see below).
|
2020-03-30 06:34:45 +00:00
|
|
|
However, this may change in the future.
|
2020-03-30 10:28:41 +00:00
|
|
|
Therefore, to ensure that magic links are not resolved,
|
|
|
|
the caller should explicitly specify
|
|
|
|
.BR RESOLVE_NO_MAGICLINKS .
|
2020-03-30 06:34:45 +00:00
|
|
|
.TP
|
|
|
|
.B RESOLVE_IN_ROOT
|
2020-03-31 07:39:22 +00:00
|
|
|
.\" commit 8db52c7e7ee1bd861b6096fcafc0fe7d0f24a994
|
2020-03-30 19:41:47 +00:00
|
|
|
Treat the directory referred to by
|
2020-03-30 06:34:45 +00:00
|
|
|
.I dirfd
|
|
|
|
as the root directory while resolving
|
2020-03-30 12:41:07 +00:00
|
|
|
.IR pathname .
|
2020-03-30 19:52:32 +00:00
|
|
|
Absolute symbolic links are interpreted relative to
|
2020-03-30 06:34:45 +00:00
|
|
|
.IR dirfd .
|
2020-03-30 19:52:32 +00:00
|
|
|
If a prefix component of
|
|
|
|
.I pathname
|
|
|
|
equates to
|
|
|
|
.IR dirfd ,
|
|
|
|
then an immediately following
|
2020-06-12 19:54:55 +00:00
|
|
|
.IR ..\&
|
2020-03-30 19:52:32 +00:00
|
|
|
component likewise equates to
|
|
|
|
.IR dirfd
|
|
|
|
(just as
|
2020-06-12 19:54:55 +00:00
|
|
|
.I /..\&
|
2020-03-30 19:52:32 +00:00
|
|
|
is traditionally equivalent to
|
|
|
|
.IR / ).
|
2020-03-30 06:34:45 +00:00
|
|
|
If
|
|
|
|
.I pathname
|
2020-03-30 19:52:32 +00:00
|
|
|
is an absolute path, it is also interpreted relative to
|
2020-03-30 06:34:45 +00:00
|
|
|
.IR dirfd .
|
2020-03-30 07:37:03 +00:00
|
|
|
.IP
|
2020-03-30 12:41:07 +00:00
|
|
|
The effect of this flag is as though the calling process had used
|
|
|
|
.BR chroot (2)
|
|
|
|
to (temporarily) modify its root directory (to the directory
|
|
|
|
referred to by
|
|
|
|
.IR dirfd ).
|
2020-03-30 06:34:45 +00:00
|
|
|
However, unlike
|
|
|
|
.BR chroot (2)
|
|
|
|
(which changes the filesystem root permanently for a process),
|
|
|
|
.B RESOLVE_IN_ROOT
|
2020-03-30 19:41:47 +00:00
|
|
|
allows a program to efficiently restrict path resolution on a per-open basis.
|
2020-03-30 07:37:03 +00:00
|
|
|
.IP
|
2020-03-30 19:17:52 +00:00
|
|
|
Currently, this flag also disables magic-link resolution.
|
2020-03-30 06:34:45 +00:00
|
|
|
However, this may change in the future.
|
2020-03-30 10:28:41 +00:00
|
|
|
Therefore, to ensure that magic links are not resolved,
|
|
|
|
the caller should explicitly specify
|
|
|
|
.BR RESOLVE_NO_MAGICLINKS .
|
2020-03-31 07:10:05 +00:00
|
|
|
.TP
|
|
|
|
.B RESOLVE_NO_MAGICLINKS
|
2020-03-31 07:39:22 +00:00
|
|
|
.\" commit 278121417a72d87fb29dd8c48801f80821e8f75a
|
2020-03-31 07:10:05 +00:00
|
|
|
Disallow all magic-link resolution during path resolution.
|
|
|
|
.IP
|
2020-04-13 07:21:20 +00:00
|
|
|
Magic links are symbolic link-like objects that are most notably found in
|
|
|
|
.BR proc (5);
|
|
|
|
examples include
|
|
|
|
.IR /proc/[pid]/exe
|
|
|
|
and
|
|
|
|
.IR /proc/[pid]/fd/* .
|
|
|
|
(See
|
|
|
|
.BR symlink (7)
|
|
|
|
for more details.)
|
|
|
|
.IP
|
|
|
|
Unknowingly opening magic links can be risky for some applications.
|
|
|
|
Examples of such risks include the following:
|
|
|
|
.RS
|
|
|
|
.IP \(bu 2
|
|
|
|
If the process opening a pathname is a controlling process that
|
|
|
|
currently has no controlling terminal (see
|
|
|
|
.BR credentials (7)),
|
|
|
|
then opening a magic link inside
|
|
|
|
.IR /proc/[pid]/fd
|
|
|
|
that happens to refer to a terminal
|
|
|
|
would cause the process to acquire a controlling terminal.
|
|
|
|
.IP \(bu
|
|
|
|
.\" From https://lwn.net/Articles/796868/:
|
|
|
|
.\" The presence of this flag will prevent a path lookup operation
|
|
|
|
.\" from traversing through one of these magic links, thus blocking
|
|
|
|
.\" (for example) attempts to escape from a container via a /proc
|
|
|
|
.\" entry for an open file descriptor.
|
|
|
|
In a containerized environment,
|
|
|
|
a magic link inside
|
|
|
|
.I /proc
|
|
|
|
may refer to an object outside the container,
|
|
|
|
and thus may provide a means to escape from the container.
|
|
|
|
.RE
|
|
|
|
.IP
|
|
|
|
Because of such risks,
|
|
|
|
an application may prefer to disable magic link resolution using the
|
|
|
|
.BR RESOLVE_NO_MAGICLINKS
|
|
|
|
flag.
|
|
|
|
.IP
|
2020-03-31 07:10:05 +00:00
|
|
|
If the trailing component (i.e., basename) of
|
|
|
|
.I pathname
|
2020-04-14 20:07:39 +00:00
|
|
|
is a magic link,
|
|
|
|
.I how.resolve
|
|
|
|
contains
|
|
|
|
.BR RESOLVE_NO_MAGICLINKS ,
|
|
|
|
and
|
2020-03-31 07:10:05 +00:00
|
|
|
.I how.flags
|
|
|
|
contains both
|
|
|
|
.BR O_PATH
|
|
|
|
and
|
|
|
|
.BR O_NOFOLLOW ,
|
|
|
|
then an
|
|
|
|
.B O_PATH
|
|
|
|
file descriptor referencing the magic link will be returned.
|
|
|
|
.TP
|
|
|
|
.B RESOLVE_NO_SYMLINKS
|
2020-03-31 07:39:22 +00:00
|
|
|
.\" commit 278121417a72d87fb29dd8c48801f80821e8f75a
|
2020-03-31 07:10:05 +00:00
|
|
|
Disallow resolution of symbolic links during path resolution.
|
|
|
|
This option implies
|
|
|
|
.BR RESOLVE_NO_MAGICLINKS .
|
|
|
|
.IP
|
|
|
|
If the trailing component (i.e., basename) of
|
|
|
|
.I pathname
|
2020-04-14 20:07:39 +00:00
|
|
|
is a symbolic link,
|
2020-06-09 12:48:01 +00:00
|
|
|
.I how.resolve
|
2020-04-14 20:07:39 +00:00
|
|
|
contains
|
|
|
|
.BR RESOLVE_NO_SYMLINKS ,
|
|
|
|
and
|
2020-03-31 07:10:05 +00:00
|
|
|
.I how.flags
|
|
|
|
contains both
|
|
|
|
.BR O_PATH
|
|
|
|
and
|
|
|
|
.BR O_NOFOLLOW ,
|
|
|
|
then an
|
|
|
|
.B O_PATH
|
|
|
|
file descriptor referencing the symbolic link will be returned.
|
|
|
|
.IP
|
2020-03-31 07:39:22 +00:00
|
|
|
Note that the effect of the
|
|
|
|
.BR RESOLVE_NO_SYMLINKS
|
|
|
|
flag,
|
|
|
|
which affects the treatment of symbolic links in all of the components of
|
|
|
|
.IR pathname ,
|
|
|
|
differs from the effect of the
|
|
|
|
.BR O_NOFOLLOW
|
|
|
|
file creation flag (in
|
|
|
|
.IR how.flags ),
|
|
|
|
which affects the handling of symbolic links only in the final component of
|
|
|
|
.IR pathname .
|
|
|
|
.IP
|
2020-04-13 07:21:20 +00:00
|
|
|
Applications that employ the
|
|
|
|
.BR RESOLVE_NO_SYMLINKS
|
|
|
|
flag are encouraged to make its use configurable
|
|
|
|
(unless it is used for a specific security purpose),
|
|
|
|
as symbolic links are very widely used by end-users.
|
|
|
|
Setting this flag indiscriminately\(emi.e.,
|
|
|
|
for purposes not specifically related to security\(emfor all uses of
|
2020-03-31 07:10:05 +00:00
|
|
|
.BR openat2 ()
|
2020-10-25 12:12:57 +00:00
|
|
|
may result in spurious errors on previously functional systems.
|
2020-04-13 07:21:20 +00:00
|
|
|
This may occur if, for example,
|
|
|
|
a system pathname that is used by an application is modified
|
|
|
|
(e.g., in a new distribution release)
|
|
|
|
so that a pathname component (now) contains a symbolic link.
|
2020-03-31 07:10:05 +00:00
|
|
|
.TP
|
|
|
|
.B RESOLVE_NO_XDEV
|
2020-03-31 07:39:22 +00:00
|
|
|
.\" commit 72ba29297e1439efaa54d9125b866ae9d15df339
|
2020-03-31 07:10:05 +00:00
|
|
|
Disallow traversal of mount points during path resolution (including all bind
|
|
|
|
mounts).
|
2020-03-31 07:39:22 +00:00
|
|
|
Consequently,
|
|
|
|
.I pathname
|
|
|
|
must either be on the same mount as the directory referred to by
|
|
|
|
.IR dirfd ,
|
|
|
|
or on the same mount as the current working directory if
|
|
|
|
.I dirfd
|
|
|
|
is specified as
|
|
|
|
.BR AT_FDCWD .
|
2020-03-31 07:10:05 +00:00
|
|
|
.IP
|
2020-04-01 06:18:45 +00:00
|
|
|
Applications that employ the
|
|
|
|
.B RESOLVE_NO_XDEV
|
|
|
|
flag are encouraged to make its use configurable (unless it is
|
|
|
|
used for a specific security purpose),
|
|
|
|
as bind mounts are widely used by end-users.
|
2020-04-01 06:16:40 +00:00
|
|
|
Setting this flag indiscriminately\(emi.e.,
|
|
|
|
for purposes not specifically related to security\(emfor all uses of
|
2020-03-31 07:10:05 +00:00
|
|
|
.BR openat2 ()
|
2020-10-25 12:12:57 +00:00
|
|
|
may result in spurious errors on previously functional systems.
|
2020-04-01 06:16:40 +00:00
|
|
|
This may occur if, for example,
|
|
|
|
a system pathname that is used by an application is modified
|
|
|
|
(e.g., in a new distribution release)
|
|
|
|
so that a pathname component (now) contains a bind mount.
|
2021-02-21 13:12:31 +00:00
|
|
|
.TP
|
|
|
|
.B RESOLVE_CACHED
|
|
|
|
Make the open operation fail unless all path components are already present
|
|
|
|
in the kernel's lookup cache.
|
|
|
|
If any kind of revalidation or I/O is needed to satisfy the lookup,
|
|
|
|
.BR openat2 ()
|
|
|
|
fails with the error
|
|
|
|
.B EAGAIN .
|
|
|
|
This is useful in providing a fast-path open that can be performed without
|
|
|
|
resorting to thread offload, or other mechanisms that an application might
|
|
|
|
use to offload slower operations.
|
2020-03-30 07:37:03 +00:00
|
|
|
.RE
|
2020-03-30 10:28:41 +00:00
|
|
|
.IP
|
2020-03-30 19:20:41 +00:00
|
|
|
If any bits other than those listed above are set in
|
|
|
|
.IR how.resolve ,
|
|
|
|
an error is returned.
|
2020-03-30 06:34:45 +00:00
|
|
|
.SH RETURN VALUE
|
|
|
|
On success, a new file descriptor is returned.
|
2020-03-30 07:54:06 +00:00
|
|
|
On error, \-1 is returned, and
|
2020-03-30 06:34:45 +00:00
|
|
|
.I errno
|
2021-01-07 07:12:28 +00:00
|
|
|
is set to indicate the error.
|
2020-03-30 06:34:45 +00:00
|
|
|
.SH ERRORS
|
|
|
|
The set of errors returned by
|
|
|
|
.BR openat2 ()
|
|
|
|
includes all of the errors returned by
|
|
|
|
.BR openat (2),
|
|
|
|
as well as the following additional errors:
|
|
|
|
.TP
|
|
|
|
.B E2BIG
|
2020-03-30 10:28:41 +00:00
|
|
|
An extension that this kernel does not support was specified in
|
|
|
|
.IR how .
|
|
|
|
(See the "Extensibility" section of
|
2020-03-30 06:34:45 +00:00
|
|
|
.B NOTES
|
|
|
|
for more detail on how extensions are handled.)
|
|
|
|
.TP
|
|
|
|
.B EAGAIN
|
2020-03-30 09:48:03 +00:00
|
|
|
.I how.resolve
|
2020-03-30 06:34:45 +00:00
|
|
|
contains either
|
2020-03-30 12:49:20 +00:00
|
|
|
.BR RESOLVE_IN_ROOT
|
|
|
|
or
|
|
|
|
.BR RESOLVE_BENEATH ,
|
2020-03-30 06:34:45 +00:00
|
|
|
and the kernel could not ensure that a ".." component didn't escape (due to a
|
2020-03-30 10:28:41 +00:00
|
|
|
race condition or potential attack).
|
|
|
|
The caller may choose to retry the
|
2020-03-30 06:34:45 +00:00
|
|
|
.BR openat2 ()
|
|
|
|
call.
|
|
|
|
.TP
|
2021-02-21 13:12:31 +00:00
|
|
|
.B EAGAIN
|
|
|
|
.BR RESOLVE_CACHED
|
|
|
|
was set, and the open operation cannot be performed using only cached
|
localedef.1, access.2, ioctl_console.2, ioctl_fslabel.2, openat2.2, write.2, dlsym.3, getopt.3, nl_langinfo.3, termios.3, xcrypt.3, hosts.equiv.5, nsswitch.conf.5, cgroups.7, man-pages.7, netlink.7, system_data_types.7: srcfix: semantic newlines
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2021-08-08 22:26:25 +00:00
|
|
|
information.
|
|
|
|
The caller should retry without
|
2021-02-21 13:12:31 +00:00
|
|
|
.B RESOLVE_CACHED
|
|
|
|
set in
|
|
|
|
.I how.resolve .
|
|
|
|
.TP
|
2020-03-30 08:17:22 +00:00
|
|
|
.B EINVAL
|
|
|
|
An unknown flag or invalid value was specified in
|
|
|
|
.IR how .
|
2020-03-30 06:34:45 +00:00
|
|
|
.TP
|
2020-03-30 08:17:22 +00:00
|
|
|
.B EINVAL
|
|
|
|
.I mode
|
2020-10-22 20:43:25 +00:00
|
|
|
is nonzero, but
|
2020-03-30 09:48:03 +00:00
|
|
|
.I how.flags
|
2020-03-30 08:17:22 +00:00
|
|
|
does not contain
|
2020-03-30 12:49:20 +00:00
|
|
|
.BR O_CREAT
|
|
|
|
or
|
|
|
|
.BR O_TMPFILE .
|
2020-03-30 08:17:22 +00:00
|
|
|
.TP
|
|
|
|
.B EINVAL
|
|
|
|
.I size
|
|
|
|
was smaller than any known version of
|
|
|
|
.IR "struct open_how" .
|
2020-03-30 06:34:45 +00:00
|
|
|
.TP
|
|
|
|
.B ELOOP
|
2020-03-30 09:48:03 +00:00
|
|
|
.I how.resolve
|
2020-03-30 06:34:45 +00:00
|
|
|
contains
|
|
|
|
.BR RESOLVE_NO_SYMLINKS ,
|
|
|
|
and one of the path components was a symbolic link (or magic link).
|
|
|
|
.TP
|
|
|
|
.B ELOOP
|
2020-03-30 09:48:03 +00:00
|
|
|
.I how.resolve
|
2020-03-30 06:34:45 +00:00
|
|
|
contains
|
|
|
|
.BR RESOLVE_NO_MAGICLINKS ,
|
|
|
|
and one of the path components was a magic link.
|
2020-03-30 08:17:22 +00:00
|
|
|
.TP
|
|
|
|
.B EXDEV
|
2020-03-30 09:48:03 +00:00
|
|
|
.I how.resolve
|
2020-03-30 08:17:22 +00:00
|
|
|
contains either
|
2020-03-30 12:49:20 +00:00
|
|
|
.BR RESOLVE_IN_ROOT
|
|
|
|
or
|
|
|
|
.BR RESOLVE_BENEATH ,
|
2020-03-30 08:17:22 +00:00
|
|
|
and an escape from the root during path resolution was detected.
|
|
|
|
.TP
|
|
|
|
.B EXDEV
|
2020-03-30 09:48:03 +00:00
|
|
|
.I how.resolve
|
2020-03-30 08:17:22 +00:00
|
|
|
contains
|
|
|
|
.BR RESOLVE_NO_XDEV ,
|
2020-03-30 10:28:41 +00:00
|
|
|
and a path component crosses a mount point.
|
2020-03-30 06:34:45 +00:00
|
|
|
.SH VERSIONS
|
|
|
|
.BR openat2 ()
|
|
|
|
first appeared in Linux 5.6.
|
2020-03-31 07:39:22 +00:00
|
|
|
.\" commit fddb5d430ad9fa91b49b1d34d0202ffe2fa0e179
|
2020-03-30 06:34:45 +00:00
|
|
|
.SH CONFORMING TO
|
|
|
|
This system call is Linux-specific.
|
2020-03-30 07:37:03 +00:00
|
|
|
.PP
|
2020-03-30 06:34:45 +00:00
|
|
|
The semantics of
|
|
|
|
.B RESOLVE_BENEATH
|
2020-03-30 06:53:59 +00:00
|
|
|
were modeled after FreeBSD's
|
2020-03-30 06:34:45 +00:00
|
|
|
.BR O_BENEATH .
|
|
|
|
.SH NOTES
|
|
|
|
.SS Extensibility
|
2020-03-30 10:28:41 +00:00
|
|
|
In order to allow for future extensibility,
|
2020-03-30 06:34:45 +00:00
|
|
|
.BR openat2 ()
|
2020-03-30 10:28:41 +00:00
|
|
|
requires the user-space application to specify the size of the
|
|
|
|
.I open_how
|
|
|
|
structure that it is passing.
|
2020-03-30 06:34:45 +00:00
|
|
|
By providing this information, it is possible for
|
|
|
|
.BR openat2 ()
|
2020-03-30 10:28:41 +00:00
|
|
|
to provide both forwards- and backwards-compatibility, with
|
2020-03-30 06:34:45 +00:00
|
|
|
.I size
|
2020-03-30 10:28:41 +00:00
|
|
|
acting as an implicit version number.
|
|
|
|
(Because new extension fields will always
|
|
|
|
be appended, the structure size will always increase.)
|
2020-03-30 06:34:45 +00:00
|
|
|
This extensibility design is very similar to other system calls such as
|
2020-09-29 22:35:09 +00:00
|
|
|
.BR sched_setattr (2),
|
2020-03-30 12:49:20 +00:00
|
|
|
.BR perf_event_open (2),
|
|
|
|
and
|
|
|
|
.BR clone3 (2).
|
2020-03-30 07:37:03 +00:00
|
|
|
.PP
|
2020-03-30 06:34:45 +00:00
|
|
|
If we let
|
|
|
|
.I usize
|
2020-03-30 10:28:41 +00:00
|
|
|
be the size of the structure as specified by the user-space application, and
|
2020-03-30 06:34:45 +00:00
|
|
|
.I ksize
|
2020-03-30 10:28:41 +00:00
|
|
|
be the size of the structure which the kernel supports, then there are
|
2020-03-30 06:34:45 +00:00
|
|
|
three cases to consider:
|
2020-03-30 08:22:48 +00:00
|
|
|
.IP \(bu 2
|
2020-03-30 06:34:45 +00:00
|
|
|
If
|
2020-03-30 12:49:20 +00:00
|
|
|
.IR ksize
|
|
|
|
equals
|
|
|
|
.IR usize ,
|
2020-03-30 06:34:45 +00:00
|
|
|
then there is no version mismatch and
|
|
|
|
.I how
|
|
|
|
can be used verbatim.
|
2020-03-30 08:22:48 +00:00
|
|
|
.IP \(bu
|
2020-03-30 06:34:45 +00:00
|
|
|
If
|
2020-03-30 12:49:20 +00:00
|
|
|
.IR ksize
|
|
|
|
is larger than
|
|
|
|
.IR usize ,
|
2020-03-30 10:28:41 +00:00
|
|
|
then there are some extension fields that the kernel supports
|
|
|
|
which the user-space application
|
2020-03-30 06:34:45 +00:00
|
|
|
is unaware of.
|
2020-03-30 10:28:41 +00:00
|
|
|
Because a zero value in any added extension field signifies a no-op,
|
|
|
|
the kernel
|
|
|
|
treats all of the extension fields not provided by the user-space application
|
|
|
|
as having zero values.
|
2020-03-30 06:34:45 +00:00
|
|
|
This provides backwards-compatibility.
|
2020-03-30 08:22:48 +00:00
|
|
|
.IP \(bu
|
2020-03-30 06:34:45 +00:00
|
|
|
If
|
2020-03-30 12:49:20 +00:00
|
|
|
.IR ksize
|
|
|
|
is smaller than
|
|
|
|
.IR usize ,
|
2020-03-30 10:28:41 +00:00
|
|
|
then there are some extension fields which the user-space application
|
|
|
|
is aware of but which the kernel does not support.
|
|
|
|
Because any extension field must have its zero values signify a no-op,
|
|
|
|
the kernel can
|
2020-03-30 06:34:45 +00:00
|
|
|
safely ignore the unsupported extension fields if they are all-zero.
|
2020-10-22 20:43:25 +00:00
|
|
|
If any unsupported extension fields are nonzero, then \-1 is returned and
|
2020-03-30 06:34:45 +00:00
|
|
|
.I errno
|
|
|
|
is set to
|
|
|
|
.BR E2BIG .
|
|
|
|
This provides forwards-compatibility.
|
|
|
|
.PP
|
2020-03-30 10:28:41 +00:00
|
|
|
Because the definition of
|
2020-03-30 06:34:45 +00:00
|
|
|
.I struct open_how
|
|
|
|
may change in the future (with new fields being added when system headers are
|
2020-03-30 10:28:41 +00:00
|
|
|
updated), user-space applications should zero-fill
|
2020-03-30 06:34:45 +00:00
|
|
|
.I struct open_how
|
2020-03-30 10:28:41 +00:00
|
|
|
to ensure that recompiling the program with new headers will not result in
|
2020-03-30 06:46:16 +00:00
|
|
|
spurious errors at runtime.
|
|
|
|
The simplest way is to use a designated
|
2020-03-30 06:53:59 +00:00
|
|
|
initializer:
|
2020-03-30 06:34:45 +00:00
|
|
|
.PP
|
|
|
|
.in +4n
|
|
|
|
.EX
|
2020-03-30 08:22:48 +00:00
|
|
|
struct open_how how = { .flags = O_RDWR,
|
|
|
|
.resolve = RESOLVE_IN_ROOT };
|
2020-03-30 06:34:45 +00:00
|
|
|
.EE
|
|
|
|
.in
|
|
|
|
.PP
|
2020-03-30 10:28:41 +00:00
|
|
|
or explicitly using
|
|
|
|
.BR memset (3)
|
|
|
|
or similar:
|
2020-03-30 06:34:45 +00:00
|
|
|
.PP
|
|
|
|
.in +4n
|
|
|
|
.EX
|
|
|
|
struct open_how how;
|
|
|
|
memset(&how, 0, sizeof(how));
|
|
|
|
how.flags = O_RDWR;
|
|
|
|
how.resolve = RESOLVE_IN_ROOT;
|
|
|
|
.EE
|
|
|
|
.in
|
|
|
|
.PP
|
2020-03-30 10:28:41 +00:00
|
|
|
A user-space application that wishes to determine which extensions
|
|
|
|
the running kernel supports can do so by conducting a binary search on
|
2020-03-30 06:34:45 +00:00
|
|
|
.IR size
|
2020-03-30 10:28:41 +00:00
|
|
|
with a structure which has every byte nonzero (to find the largest value
|
2020-03-30 06:46:16 +00:00
|
|
|
which doesn't produce an error of
|
2020-03-30 10:28:41 +00:00
|
|
|
.BR E2BIG ).
|
2020-03-30 06:34:45 +00:00
|
|
|
.SH SEE ALSO
|
|
|
|
.BR openat (2),
|
|
|
|
.BR path_resolution (7),
|
|
|
|
.BR symlink (7)
|