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Re: [PATCH] Linux: Add memfd_create system call wrapper
On Thu, Nov 16, 2017 at 08:34:26AM -0200, Adhemerval Zanella wrote:
>
>
> On 12/11/2017 12:51, Florian Weimer wrote:
> > On 11/12/2017 10:04 AM, Florian Weimer wrote:
> >> If that's not acceptable, we should probably not add <sys/memfd.h> at
> >> all, but replicate the UAPI constants in <sys/mman.h>.
+1 that sounds like a good idea.
> >>
> >> I see that this also affects the test. So we probably should go the
> >> <sys/mman.h> route.
> >
> > I had already taken care of that, I forgot. Anyway, the attached patch has the <sys/mman.h> variant of the system call wrapper.
> >
> > Thanks,
> > Florian
> >
> > memfd.patch
> >
> >
> > The system call is somewhat obscure because it is closely related
> > to file descriptor sealing. However, it is also the recommended
Sure and the api is somewhat bogus given this nonesensical "name" argument in
there but it actually has a lot more use-cases for userspace.
> > way to create alias mappings, which is why it has more general use.
For example, systemd and lxc both carry their own memfd_create() definitions
including the appropriate syscall number and option numbers. A concrete use-case
is e.g. using mmap() + memfd_create() to create an efficient (Linux specific)
in-memory ringbuffer ( https://github.com/lxc/lxc/blob/master/src/lxc/ringbuf.c
). In general, both have valid use cases to only have an in-memory file that
can't be covered by mmap() alone. So this is really good to finally have!
> >
> > No emulation is provided. Except for the name of the
> > /proc/self/fd links, it would be possible to implement an
> > approximation using O_TMPFILE and tmpfs, but this does not appear
> > to be worth the added complexity.
> >
> > 2017-11-12 Florian Weimer <fweimer@redhat.com>
> >
> > Linux: Add memfd_create system call wrapper
> > * sysdeps/unix/sysv/linux/Makefile [misc] (tests): Add
> > tst-memfd_create.
> > * sysdeps/unix/sysv/linux/bits/mman-linux.h [__USE_GNU]
> > (MFD_CLOEXEC, MFD_ALLOW_SEALING): Define.
> > [__USE_GNU] (memfd_create): Declare.
> > * sysdeps/unix/sysv/linux/Versions (GLIBC_2.27): Add memfd_create.
> > * sysdeps/unix/sysv/linux/syscalls.list (memfd_create): Add.
> > * sysdeps/unix/sysv/linux/tst-memfd_create.c: New file.
> > * sysdeps/unix/sysv/linux/**.abilist: Update.
> > * manual/llio.texi (Memory-mapped I/O): Document memfd_create.
>
> LGTM with just an update below.
>
> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
>
> >
> > diff --git a/NEWS b/NEWS
> > index b7281621f4..eca0c00a9b 100644
> > --- a/NEWS
> > +++ b/NEWS
> > @@ -35,6 +35,9 @@ Major new features:
> > are the same interfaces added in version 2.26 for some platforms where
> > this format is supported but is not the format of long double.
> >
> > +* glibc now provides the <sys/memfd.h> header file and the memfd_create
> > + system call.
> > +
> > Deprecated and removed features, and other changes affecting compatibility:
> >
> > * On GNU/Linux, the obsolete Linux constant PTRACE_SEIZE_DEVEL is no longer
>
> Ok.
>
> > diff --git a/manual/llio.texi b/manual/llio.texi
> > index 10ad546723..59eb3af711 100644
> > --- a/manual/llio.texi
> > +++ b/manual/llio.texi
> > @@ -1775,6 +1775,40 @@ the given @var{name} previously created by @code{shm_open}.
> > On failure @code{errno} is set.
> > @end deftypefn
> >
> > +@deftypefn Function int memfd_create (const char *@var{name}, unsigned int flags)
> > +@standards{Linux, sys/mman.h}
> > +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{@acsfd{}}}
> > +The @code{memfd_create} function returns a file descriptor which can be
> > +used to create memory mappings using the @code{mmap} function. It is
> > +similar to the @code{shm_open} function in the sense that these mappings
> > +are not backed by actual files. However, the descriptor return by
> > +@code{memfd_create} does not correspond to a named object; the
> > +@var{name} argument is used for informative purposes only. The
> > +descriptor can be passed between processes (for example, over local
> > +domain sockets), and mappings at the same offset refer to the same
> > +memory, or the descriptor can be used to create alias mappings within
> > +the same process.
> > +
> > +The descriptor initially refers to a zero-length file. Before mappings
> > +can be created which are backed by memory, the file size needs to be
> > +increased with the @code{ftruncate} function. @xref{File Size}.
> > +
> > +The @var{flags} argument can be a combination of the following flags:
> > +
> > +@table @code
> > +@item MFD_CLOEXEC
> > +The descriptor is created with the @code{O_CLOEXEC} flag.
> > +
> > +@item MFD_ALLOW_SEALING
> > +The descriptor supports the addition of seals using the @code{fcntl}
> > +function.
> > +@end table
> > +
> > +The @code{memfd_create} function is specific to Linux.
> > +
> > +@end deftypefn
> > +
> > +
> > @node Waiting for I/O
> > @section Waiting for Input or Output
> > @cindex waiting for input or output
>
> Linux 4.14 (749df87bd7be) added a new flag MFD_HUGETLB. I think ww should add
> and document it.
>
> > diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> > index bf76b8773d..f974ac446b 100644
> > --- a/sysdeps/unix/sysv/linux/Makefile
> > +++ b/sysdeps/unix/sysv/linux/Makefile
> > @@ -43,7 +43,8 @@ sysdep_headers += sys/mount.h sys/acct.h sys/sysctl.h \
> > bits/siginfo-arch.h bits/siginfo-consts-arch.h
> >
> > tests += tst-clone tst-clone2 tst-clone3 tst-fanotify tst-personality \
> > - tst-quota tst-sync_file_range test-errno-linux tst-sysconf-iov_max
> > + tst-quota tst-sync_file_range test-errno-linux tst-sysconf-iov_max \
> > + tst-memfd_create
> >
> > # Generate the list of SYS_* macros for the system calls (__NR_*
> > # macros). The file syscall-names.list contains all possible system
>
> Ok.
>
> > diff --git a/sysdeps/unix/sysv/linux/Versions b/sysdeps/unix/sysv/linux/Versions
> > index d3dbcde8c9..6f2fe516d7 100644
> > --- a/sysdeps/unix/sysv/linux/Versions
> > +++ b/sysdeps/unix/sysv/linux/Versions
> > @@ -166,6 +166,9 @@ libc {
> > GLIBC_2.15 {
> > process_vm_readv; process_vm_writev;
> > }
> > + GLIBC_2.27 {
> > + memfd_create;
> > + }
> > GLIBC_PRIVATE {
> > # functions used in other libraries
> > __syscall_rt_sigqueueinfo;
>
> Ok.
>
> > diff --git a/sysdeps/unix/sysv/linux/aarch64/libc.abilist b/sysdeps/unix/sysv/linux/aarch64/libc.abilist
> > index ed598aedac..140ca28abc 100644
> > --- a/sysdeps/unix/sysv/linux/aarch64/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/aarch64/libc.abilist
> > @@ -2106,6 +2106,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.27 strfromf128 F
> > GLIBC_2.27 strtof128 F
> > GLIBC_2.27 strtof128_l F
> > diff --git a/sysdeps/unix/sysv/linux/alpha/libc.abilist b/sysdeps/unix/sysv/linux/alpha/libc.abilist
> > index 4e57f36bcf..f698e1b2f4 100644
> > --- a/sysdeps/unix/sysv/linux/alpha/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/alpha/libc.abilist
> > @@ -2017,6 +2017,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.27 strfromf128 F
> > GLIBC_2.27 strtof128 F
> > GLIBC_2.27 strtof128_l F
> > diff --git a/sysdeps/unix/sysv/linux/arm/libc.abilist b/sysdeps/unix/sysv/linux/arm/libc.abilist
> > index 5b70e1bfc9..8a8af3e3e4 100644
> > --- a/sysdeps/unix/sysv/linux/arm/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/arm/libc.abilist
> > @@ -107,6 +107,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.4 GLIBC_2.4 A
> > GLIBC_2.4 _Exit F
> > GLIBC_2.4 _IO_2_1_stderr_ D 0xa0
> > diff --git a/sysdeps/unix/sysv/linux/bits/mman-linux.h b/sysdeps/unix/sysv/linux/bits/mman-linux.h
> > index b091181960..396829482a 100644
> > --- a/sysdeps/unix/sysv/linux/bits/mman-linux.h
> > +++ b/sysdeps/unix/sysv/linux/bits/mman-linux.h
> > @@ -109,3 +109,18 @@
> > # define MCL_ONFAULT 4 /* Lock all pages that are
> > faulted in. */
> > #endif
> > +
> > +#ifdef __USE_GNU
> > +/* Flags for memfd_create. */
> > +# define MFD_CLOEXEC 1U
> > +# define MFD_ALLOW_SEALING 2U
> > +
> > +__BEGIN_DECLS
> > +
> > +/* Create a new memory file descriptor. NAME is a name for debugging.
> > + FLAGS is a combination of the MFD_* constants. */
> > +int memfd_create (const char *__name, unsigned int __flags) __THROW;
> > +
> > +__END_DECLS
> > +
> > +#endif /* __USE_GNU */
>
> As before I think we should include MFD_HUGETLB.
>
> > diff --git a/sysdeps/unix/sysv/linux/hppa/libc.abilist b/sysdeps/unix/sysv/linux/hppa/libc.abilist
> > index 6a2500a8b3..5b81a6cd7d 100644
> > --- a/sysdeps/unix/sysv/linux/hppa/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/hppa/libc.abilist
> > @@ -1871,6 +1871,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/i386/libc.abilist b/sysdeps/unix/sysv/linux/i386/libc.abilist
> > index 9ab4e3642a..51ead9e867 100644
> > --- a/sysdeps/unix/sysv/linux/i386/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/i386/libc.abilist
> > @@ -2036,6 +2036,7 @@ GLIBC_2.26 wcstof128_l F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/ia64/libc.abilist b/sysdeps/unix/sysv/linux/ia64/libc.abilist
> > index 81bb623fe8..78b4ee8d40 100644
> > --- a/sysdeps/unix/sysv/linux/ia64/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/ia64/libc.abilist
> > @@ -1900,6 +1900,7 @@ GLIBC_2.26 wcstof128_l F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist b/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
> > index 5a33b57390..d9c97779e4 100644
> > --- a/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/m68k/coldfire/libc.abilist
> > @@ -108,6 +108,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.4 GLIBC_2.4 A
> > GLIBC_2.4 _Exit F
> > GLIBC_2.4 _IO_2_1_stderr_ D 0x98
> > diff --git a/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist b/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
> > index 50a86e74fa..4acbf7eeed 100644
> > --- a/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/m68k/m680x0/libc.abilist
> > @@ -1985,6 +1985,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/microblaze/libc.abilist b/sysdeps/unix/sysv/linux/microblaze/libc.abilist
> > index 250ef305c3..93f02f08ce 100644
> > --- a/sysdeps/unix/sysv/linux/microblaze/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/microblaze/libc.abilist
> > @@ -2106,3 +2106,4 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > diff --git a/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist
> > index 87a1dc4ad7..795e85de70 100644
> > --- a/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/mips/mips32/fpu/libc.abilist
> > @@ -1960,6 +1960,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist
> > index f2b35f250e..dc714057b7 100644
> > --- a/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/mips/mips32/nofpu/libc.abilist
> > @@ -1958,6 +1958,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist
> > index ade654dbea..ce7bc9b175 100644
> > --- a/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/mips/mips64/n32/libc.abilist
> > @@ -1956,6 +1956,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.27 strfromf128 F
> > GLIBC_2.27 strtof128 F
> > GLIBC_2.27 strtof128_l F
> > diff --git a/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist b/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist
> > index 56032c3f82..3fdd85eace 100644
> > --- a/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/mips/mips64/n64/libc.abilist
> > @@ -1951,6 +1951,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.27 strfromf128 F
> > GLIBC_2.27 strtof128 F
> > GLIBC_2.27 strtof128_l F
> > diff --git a/sysdeps/unix/sysv/linux/nios2/libc.abilist b/sysdeps/unix/sysv/linux/nios2/libc.abilist
> > index c599dd9212..3e0bcb2a5c 100644
> > --- a/sysdeps/unix/sysv/linux/nios2/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/nios2/libc.abilist
> > @@ -2147,3 +2147,4 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist b/sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist
> > index 385409aa6e..375c69d9d1 100644
> > --- a/sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libc.abilist
> > @@ -1989,6 +1989,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist b/sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist
> > index e99cb454b5..a88172a906 100644
> > --- a/sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libc.abilist
> > @@ -1994,6 +1994,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/libc-le.abilist b/sysdeps/unix/sysv/linux/powerpc/powerpc64/libc-le.abilist
> > index 173672ab5e..fa026a332c 100644
> > --- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/libc-le.abilist
> > +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/libc-le.abilist
> > @@ -2201,3 +2201,4 @@ GLIBC_2.26 wcstof128_l F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/libc.abilist b/sysdeps/unix/sysv/linux/powerpc/powerpc64/libc.abilist
> > index 8a654436ab..838f395d78 100644
> > --- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/libc.abilist
> > @@ -108,6 +108,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 _Exit F
> > GLIBC_2.3 _IO_2_1_stderr_ D 0xe0
> > diff --git a/sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist b/sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist
> > index dbd411ceb1..41b79c496a 100644
> > --- a/sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/s390/s390-32/libc.abilist
> > @@ -1989,6 +1989,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.27 strfromf128 F
> > GLIBC_2.27 strtof128 F
> > GLIBC_2.27 strtof128_l F
> > diff --git a/sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist b/sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist
> > index 5617784ca0..68251a0e69 100644
> > --- a/sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/s390/s390-64/libc.abilist
> > @@ -1890,6 +1890,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.27 strfromf128 F
> > GLIBC_2.27 strtof128 F
> > GLIBC_2.27 strtof128_l F
> > diff --git a/sysdeps/unix/sysv/linux/sh/libc.abilist b/sysdeps/unix/sysv/linux/sh/libc.abilist
> > index 0f840e6e88..bc1aae275e 100644
> > --- a/sysdeps/unix/sysv/linux/sh/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/sh/libc.abilist
> > @@ -1875,6 +1875,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist b/sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist
> > index bb7e1042c7..93e6d092ac 100644
> > --- a/sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/sparc/sparc32/libc.abilist
> > @@ -1982,6 +1982,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.27 strfromf128 F
> > GLIBC_2.27 strtof128 F
> > GLIBC_2.27 strtof128_l F
> > diff --git a/sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist b/sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist
> > index 4053b0a51c..b11d6764d4 100644
> > --- a/sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/sparc/sparc64/libc.abilist
> > @@ -1919,6 +1919,7 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.27 strfromf128 F
> > GLIBC_2.27 strtof128 F
> > GLIBC_2.27 strtof128_l F
> > diff --git a/sysdeps/unix/sysv/linux/syscalls.list b/sysdeps/unix/sysv/linux/syscalls.list
> > index 8bfb080d80..40c4fbb9ea 100644
> > --- a/sysdeps/unix/sysv/linux/syscalls.list
> > +++ b/sysdeps/unix/sysv/linux/syscalls.list
> > @@ -109,3 +109,4 @@ setns EXTRA setns i:ii setns
> >
> > process_vm_readv EXTRA process_vm_readv i:ipipii process_vm_readv
> > process_vm_writev EXTRA process_vm_writev i:ipipii process_vm_writev
> > +memfd_create EXTRA memfd_create i:si memfd_create
> > diff --git a/sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libc.abilist b/sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libc.abilist
> > index 38a96d3a02..e9eb4ff7bd 100644
> > --- a/sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libc.abilist
> > @@ -2113,3 +2113,4 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > diff --git a/sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libc.abilist b/sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libc.abilist
> > index 572b917d7d..8f08e909cd 100644
> > --- a/sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libc.abilist
> > @@ -2113,3 +2113,4 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > diff --git a/sysdeps/unix/sysv/linux/tile/tilepro/libc.abilist b/sysdeps/unix/sysv/linux/tile/tilepro/libc.abilist
> > index 38a96d3a02..e9eb4ff7bd 100644
> > --- a/sysdeps/unix/sysv/linux/tile/tilepro/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/tile/tilepro/libc.abilist
> > @@ -2113,3 +2113,4 @@ GLIBC_2.26 reallocarray F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > diff --git a/sysdeps/unix/sysv/linux/tst-memfd_create.c b/sysdeps/unix/sysv/linux/tst-memfd_create.c
> > new file mode 100644
> > index 0000000000..fd173ff71d
> > --- /dev/null
> > +++ b/sysdeps/unix/sysv/linux/tst-memfd_create.c
> > @@ -0,0 +1,121 @@
> > +/* Test for the memfd_create system call.
> > + Copyright (C) 2017 Free Software Foundation, Inc.
> > + This file is part of the GNU C Library.
> > +
> > + The GNU C Library is free software; you can redistribute it and/or
> > + modify it under the terms of the GNU Lesser General Public
> > + License as published by the Free Software Foundation; either
> > + version 2.1 of the License, or (at your option) any later version.
> > +
> > + The GNU C Library is distributed in the hope that it will be useful,
> > + but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> > + Lesser General Public License for more details.
> > +
> > + You should have received a copy of the GNU Lesser General Public
> > + License along with the GNU C Library; if not, see
> > + <http://www.gnu.org/licenses/>. */
> > +
> > +#include <errno.h>
> > +#include <fcntl.h>
> > +#include <stdbool.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <support/check.h>
> > +#include <support/support.h>
> > +#include <support/test-driver.h>
> > +#include <support/xunistd.h>
> > +#include <sys/mman.h>
> > +
> > +/* Return true if the descriptor has the FD_CLOEXEC flag set. */
> > +static bool
> > +is_cloexec (int fd)
> > +{
> > + int flags = fcntl (fd, F_GETFD);
> > + TEST_VERIFY (flags >= 0);
> > + return flags & FD_CLOEXEC;
> > +}
> > +
> > +/* Return the seals set on FD. */
> > +static int
> > +get_seals (int fd)
> > +{
> > + int flags = fcntl (fd, F_GET_SEALS);
> > + TEST_VERIFY (flags >= 0);
> > + return flags;
> > +}
> > +
> > +/* Return true if the F_SEAL_SEAL flag is set on the descriptor. */
> > +static bool
> > +is_sealed (int fd)
> > +{
> > + return get_seals (fd) & F_SEAL_SEAL;
> > +}
> > +
> > +static int
> > +do_test (void)
> > +{
> > + /* Initialized by the first call to memfd_create to 0 (memfd_create
> > + unsupported) or 1 (memfd_create is implemented in the kernel).
> > + Subsequent iterations check that the success/failure state is
> > + consistent. */
> > + int supported = -1;
> > +
> > + for (int do_cloexec = 0; do_cloexec < 2; ++do_cloexec)
> > + for (int do_sealing = 0; do_sealing < 2; ++do_sealing)
> > + {
> > + int flags = 0;
> > + if (do_cloexec)
> > + flags |= MFD_CLOEXEC;
> > + if (do_sealing)
> > + flags |= MFD_ALLOW_SEALING;
> > + if (test_verbose > 0)
> > + printf ("info: memfd_create with flags=0x%x\n", flags);
> > + int fd = memfd_create ("tst-memfd_create", flags);
> > + if (fd < 0)
> > + {
> > + if (errno == ENOSYS)
> > + {
> > + if (supported < 0)
> > + {
> > + printf ("warning: memfd_create is unsupported\n");
> > + supported = 0;
> > + continue;
> > + }
> > + TEST_VERIFY (supported == 0);
> > + continue;
> > + }
> > + else
> > + FAIL_EXIT1 ("memfd_create: %m");
> > + }
> > + if (supported < 0)
> > + supported = 1;
> > + TEST_VERIFY (supported > 0);
> > +
> > + char *fd_path = xasprintf ("/proc/self/fd/%d", fd);
> > + char *link = xreadlink (fd_path);
> > + if (test_verbose > 0)
> > + printf ("info: memfd link: %s\n", link);
> > + TEST_VERIFY (strcmp (link, "memfd:tst-memfd_create (deleted)"));
> > + TEST_VERIFY (is_cloexec (fd) == do_cloexec);
> > + TEST_VERIFY (is_sealed (fd) == !do_sealing);
> > + if (do_sealing)
> > + {
> > + TEST_VERIFY (fcntl (fd, F_ADD_SEALS, F_SEAL_WRITE) == 0);
> > + TEST_VERIFY (!is_sealed (fd));
> > + TEST_VERIFY (get_seals (fd) & F_SEAL_WRITE);
> > + TEST_VERIFY (fcntl (fd, F_ADD_SEALS, F_SEAL_SEAL) == 0);
> > + TEST_VERIFY (is_sealed (fd));
> > + }
> > + xclose (fd);
> > + free (fd_path);
> > + free (link);
> > + }
> > +
> > + if (supported == 0)
> > + return EXIT_UNSUPPORTED;
> > + return 0;
> > +}
> > +
> > +#include <support/test-driver.c>
>
> Ok.
>
> > diff --git a/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist b/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist
> > index b83d25c2e3..0a4f7797ac 100644
> > --- a/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/x86_64/64/libc.abilist
> > @@ -1877,6 +1877,7 @@ GLIBC_2.26 wcstof128_l F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> > GLIBC_2.3 GLIBC_2.3 A
> > GLIBC_2.3 __ctype_b_loc F
> > GLIBC_2.3 __ctype_tolower_loc F
> > diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist b/sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist
> > index cba1d59057..23f6a91429 100644
> > --- a/sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist
> > +++ b/sysdeps/unix/sysv/linux/x86_64/x32/libc.abilist
> > @@ -2120,3 +2120,4 @@ GLIBC_2.26 wcstof128_l F
> > GLIBC_2.27 GLIBC_2.27 A
> > GLIBC_2.27 glob F
> > GLIBC_2.27 glob64 F
> > +GLIBC_2.27 memfd_create F
> >