using an open_to_lock_owner4 when that lock_owner4 has already
been created by a previous open_to_lock_owner4. This caused the NFS server
to reply NFSERR_INVAL.
For NFSv4.0, this is an error, although the updated NFSv4.0 RFC7530 notes
that the correct error reply is NFSERR_BADSEQID (RFC3530 did not specify
what error to return).
For NFSv4.1, it is not obvious whether or not this is allowed by RFC5661,
but the NFSv4.1 server can handle this case without error.
This patch changes the NFSv4.1 (and NFSv4.2) server to handle multiple
uses of the same lock_owner in open_to_lock_owner so that it now correctly
interoperates with the Linux NFS client.
It also changes the error returned for NFSv4.0 to be NFSERR_BADSEQID.
Thanks go to Bjorn for diagnosing this and testing the patch.
He also provided a program that I could use to reproduce the problem.
Tested by: bj@cebitec.uni-bielefeld.de (Bjorn Fischer)
PR: 249567
Reported by: bj@cebitec.uni-bielefeld.de (Bjorn Fischer)
MFC after: 3 days
Recent testing of the NFS-over-TLS code found a LOR between the mutex lock
used for sessions and the sleep lock used for server side krpc socket
structures in nfsrv_checksequence(). This was fixed by r365789.
A similar bug exists in nfsrv_bindconnsess(), where SVC_RELEASE() is called
while mutexes are held.
This patch applies a fix similar to r365789, moving the SVC_RELEASE() call
down to after the mutexes are released.
This patch fixes the problem by moving the SVC_RELEASE() call in
nfsrv_checksequence() down a few lines to below where the mutex is released.
MFC after: 1 week
Recent testing of the NFS-over-TLS code found a LOR between the mutex lock
used for sessions and the sleep lock used for server side krpc socket
structures.
The code in nfsrv_checksequence() would call SVC_RELEASE() with the mutex
held. Normally this is ok, since all that happens is SVC_RELEASE()
decrements a reference count. However, if the socket has just been shut
down, SVC_RELEASE() drops the reference count to 0 and acquires a sleep
lock during destruction of the server side krpc structure.
This patch fixes the problem by moving the SVC_RELEASE() call in
nfsrv_checksequence() down a few lines to below where the mutex is released.
MFC after: 1 week
asomers@ reported a crash on an NFSv4.0 server with a backtrace of:
kdb_backtrace
vpanic
panic
nfsrv_docallback
nfsrv_checkgetattr
nfsrvd_getattr
nfsrvd_dorpc
nfssvc_program
svc_run_internal
svc_thread_start
fork_exit
fork_trampoline
where the panic message was "docallb", which indicates that a callback
was attempted when the ClientID is unconfirmed.
This would not normally occur, but it is possible to have an unconfirmed
ClientID structure with delegation structure(s) chained off it if the
client were to issue a SetClientID with the same "id" but different
"verifier" after acquiring delegations on the previously confirmed ClientID.
The bug appears to be that nfsrv_checkgetattr() failed to check for
this uncommon case of an unconfirmed ClientID with a delegation structure
that no longer refers to a delegation the client knows about.
This patch adds a check for this case, handling it as if no delegation
exists, which is the case when the above occurs.
Although difficult to reproduce, this change should avoid the panic().
PR: 249127
Reported by: asomers
Reviewed by: asomers
MFC after: 1 week
Differential Revision: https://reviews.freebbsd.org/D26342
An Internet Draft titled "Towards Remote Procedure Call Encryption By Default"
(soon to be an RFC I think) describes how Sun RPC is to use TLS with NFS
as a specific application case.
Various commits prepared the NFS code to use KERN_TLS, mainly enabling use
of ext_pgs mbufs for large RPC messages.
r364475 added TLS support to the kernel RPC.
This commit (which is the final one for kernel changes required to do
NFS over TLS) adds support for three export flags:
MNT_EXTLS - Requires a TLS connection.
MNT_EXTLSCERT - Requires a TLS connection where the client presents a valid
X.509 certificate during TLS handshake.
MNT_EXTLSCERTUSER - Requires a TLS connection where the client presents a
valid X.509 certificate with "user@domain" in the otherName
field of the SubjectAltName during TLS handshake.
Without these export options, clients are permitted, but not required, to
use TLS.
For the client, a new nmount(2) option called "tls" makes the client do
a STARTTLS Null RPC and TLS handshake for all TCP connections used for the
mount. The CLSET_TLS client control option is used to indicate to the kernel RPC
that this should be done.
Unless the above export flags or "tls" option is used, semantics should
not change for the NFS client nor server.
For NFS over TLS to work, the userspace daemons rpctlscd(8) { for client }
or rpctlssd(8) daemon { for server } must be running.
This is a partial revert of r363210, since the "use_ext" argument added
by that commit is not actually useful.
This patch should not result in any semantics change.
For NFSv4.0, the server creates a server->client TCP connection for callbacks.
If the client mount on the server is using TLS, enable TLS for this callback
TCP connection.
TLS connections from clients will not be supported until the kernel RPC
changes are committed.
Since this changes the internal ABI between the NFS kernel modules that
will require a version bump, delete newnfs_trimtrailing(), which is no
longer used.
Since LCL_TLSCB is not yet set, these changes should not have any semantic
affect at this time.
and getxattr operations.
This patch optionally enables generation of read, readlink and getxattr replies
in ext_pgs mbufs. Since neither of ND_EXTPG or ND_TLS are currently ever set,
there is no change in semantics at this time.
It also corrects the message in a couple of panic()s that should never occur.
This is another in the series of commits that add support to the NFS client
and server for building RPC messages in ext_pgs mbufs with anonymous pages.
This is useful so that the entire mbuf list does not need to be
copied before calling sosend() when NFS over TLS is enabled.
Use of ext_pgs mbufs will not be enabled until the kernel RPC is updated
to handle TLS.
This patch code that optionally (based on ND_TLS, never set yet) generates
readdir replies in ext_pgs mbufs.
To trim the list back, a new function that is ext_pgs aware called
nfsm_trimtrailing() replaces newnfs_trimtrailing().
newnfs_trimtrailing() is no longer used, but will be removed in a future
commit, since its removal does modify the internal kpi between the NFS
modules.
This is another in the series of commits that add support to the NFS client
and server for building RPC messages in ext_pgs mbufs with anonymous pages.
This is useful so that the entire mbuf list does not need to be
copied before calling sosend() when NFS over TLS is enabled.
Use of ext_pgs mbufs will not be enabled until the kernel RPC is updated
to handle TLS.
r362490 marked that the NFSv4 attribute TimeCreate (va_birthtime) is supported,
but it did not change the NFS server code to actually do it.
As such, errors could occur when unrolling a tarball onto an NFSv4 mounted
volume, since setting TimeCreate would fail with a NFSERR_ATTRNOTSUPP reply.
This patch fixes the server so that it does TimeCreate and also makes
sure that TimeCreate will not be set for a DS file for a pNFS server.
A separate commit will add a check to the NFSv4 client for support of
the TimeCreate attribute before attempting to set it, to avoid a problem
when mounting a server that does not support the attribute.
The failures will still occur for r362490 or later kernels that do not
have this patch, since they indicate support for the attribute, but do not
actually support the attribute.
This patch uses a slightly different algorithm for nfsrv_adj()
since ext_pgs mbuf lists are not permitted to have m_len == 0 mbufs.
As such, the code now frees mbufs after the adjustment in the list instead
of setting their m_len field to 0.
Since mbuf(s) may be trimmed off the tail of the list, the function now
returns a pointer to the last mbuf in the list. This saves the caller
from needing to use m_last() to find the last mbuf.
It also implies that it might return a nul list, which required a check for
that in nfsrvd_readlink().
This is another in the series of commits that add support to the NFS client
and server for building RPC messages in ext_pgs mbufs with anonymous pages.
This is useful so that the entire mbuf list does not need to be
copied before calling sosend() when NFS over TLS is enabled.
Use of ext_pgs mbufs will not be enabled until the kernel RPC is updated
to handle TLS.
should be used.
For KERN_TLS (and possibly some other future network interface) the mbuf
list passed into sosend() must be ext_pgs mbufs. The krpc could simply
copy all the mbuf data into ext_pgs mbufs before calling sosend(), but
that would be inefficient for large RPC messages.
This patch adds an argument to nfscl_reqstart() to indicate that it should
fill the RPC message into ext_pgs mbufs.
It also adds fields to "struct nfsrv_descript" needed for building NFS RPC
messages in ext_pgs mbufs, along with new flags for this.
Since the argument is always "false", this commit should not result in any
semantic change. However, this commit prepares the code
for future commits that will add support for building of NFS RPC messages
in ext_pgs mbufs.
These macro definitions are no longer needed as the NFS OSX port is long
dead. The vfs_statfs macro conflicts with the vfsops field of the same
name.
Submitted by: shivank@
Reviewed by: rmacklem
MFC after: 2 weeks
Sponsored by: Google, Inc. (GSoC 2020)
Differential Revision: https://reviews.freebsd.org/D25263
Since mnt_flags was upgraded to 64bits there has been a quirk in
"struct export_args", since it hold a copy of mnt_flags
in ex_flags, which is an "int" (32bits).
This happens to currently work, since all the flag bits used in ex_flags are
defined in the low order 32bits. However, new export flags cannot be defined.
Also, ex_anon is a "struct xucred", which limits it to 16 additional groups.
This patch revises "struct export_args" to make ex_flags 64bits and replaces
ex_anon with ex_uid, ex_ngroups and ex_groups (which points to a
groups list, so it can be malloc'd up to NGROUPS in size.
This requires that the VFS_CHECKEXP() arguments change, so I also modified the
last "secflavors" argument to be an array pointer, so that the
secflavors could be copied in VFS_CHECKEXP() while the export entry is locked.
(Without this patch VFS_CHECKEXP() returns a pointer to the secflavors
array and then it is used after being unlocked, which is potentially
a problem if the exports entry is changed.
In practice this does not occur when mountd is run with "-S",
but I think it is worth fixing.)
This patch also deleted the vfs_oexport_conv() function, since
do_mount_update() does the conversion, as required by the old vfs_cmount()
calls.
Reviewed by: kib, freqlabs
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D25088
Comparing fsid_t objects requires internal knowledge of the fsid structure
and yet this is duplicated across a number of places in the code.
Simplify by creating a fsidcmp function (macro).
Reviewed by: mjg, rmacklem
Approved by: mav (mentor)
MFC after: 1 week
Sponsored by: iXsystems, Inc.
Differential Revision: https://reviews.freebsd.org/D24749
mbuf lists.
This function is currently trivial, but will that will change when
support for building NFS messages in ext_pgs mbufs is added.
Adding support for ext_pgs mbufs is needed for KERN_TLS, which will
be used to implement nfs-over-tls.
The macros CAST_USER_ADDR_T() and CAST_DOWN() were used for the Mac OS/X
port. The first of these macros was a no-op for FreeBSD and the second
is no longer used.
This patch gets rid of them. It also deletes the "mbuf_t" typedef which
is no longer used in the FreeBSD code from nfskpiport.h
This patch should not change semantics.
The typedef mbuf_t was used for the Mac OS/X port of the code long ago.
Since this port is no longer used and the use of mbuf_t obscures what
the code does (and is not consistent with style(9)), it is no longer needed.
This patch replaces all instances of mbuf_t with "struct mbuf *", so that
it is no longer used.
This patch should not result in any semantic change.
Ryan Moeller reported crashes in the NFS server that appear to be
caused by stack corruption in nfsrv_compound(). It appears that
the stack got corrupted just after a NFSv4.1 Lookup that crosses
a server mount point.
Although it is just a "theory" at this point, the most obvious way
the stack could get corrupted would be if nfsvno_checkexp() somehow
acquires an export with a bogus nes_numsecflavor value. This would
cause the copying of the secflavors to run off the end of the array,
which is allocated on the stack below where the corruption occurs.
This sanity check is simple to do and would stop the stack corruption
if the theory is correct. Otherwise, doing the sanity check seems to
be a reasonable safety belt to add to the code.
Reported by: freqlabs
MFC after: 2 weeks
I missed the "atomic" field of the RemoveExtendedAttribute operation's
reply when I implemented it. It worked between FreeBSD client and server,
since it was missed for both, but it did not conform to RFC 8276.
This patch adds the field for both client and server.
Thanks go to Frank for doing interoperability testing of the extended
attribute support against patches for Linux.
Submitted by: Frank van der Linden <fllinden@amazon.com>
Reported by: Frank van der Linden <fllinden@amazon.com>
I did not realize that zero length attributes are allowed, but they are.
This patch fixes the NFSv4.2 client and server to handle zero length
extended attributes correctly.
Submitted by: Frank van der Linden <fllinden@amazon.com> (earlier version)
Reported by: Frank van der Linden <fllinder@amazon.com>
The file handle affinity code was configured to be used by both the
old and new NFS servers. This no longer makes sense, since there is
only one NFS server.
This patch copies a majority of the code in sys/nfs/nfs_fha.c and
sys/nfs/nfs_fha.h into sys/fs/nfsserver/nfs_fha_new.c and
sys/fs/nfsserver/nfs_fha_new.h, so that the files in sys/nfs can be
deleted. The code is simplified by deleting the function callback pointers
used to call functions in either the old or new NFS server and they were
replaced by calls to the functions.
As well as a cleanup, this re-organization simplifies the changes
required for handling of external page mbufs, which is required for KERN_TLS.
This patch should not result in a semantic change to file handle affinity.
When the code was ported to Mac OS/X, mbuf handling functions were
converted to using the Mac OS/X accessor functions. For FreeBSD, they
are a simple set of macros in sys/fs/nfs/nfskpiport.h.
Since porting to Mac OS/X is no longer a consideration, replacement of
these macros with the code generated by them makes the code more
readable.
When support for external page mbufs is added as needed by the KERN_TLS,
the patch becomes simpler if done without the macros.
This patch should not result in any semantic change.
When the code was ported to Mac OS/X, mbuf handling functions were
converted to using the Mac OS/X accessor functions. For FreeBSD, they
are a simple set of macros in sys/fs/nfs/nfskpiport.h.
Since porting to Mac OS/X is no longer a consideration, replacement of
these macros with the code generated by them makes the code more
readable.
When support for external page mbufs is added as needed by the KERN_TLS,
the patch becomes simpler if done without the macros.
This patch should not result in any semantic change.
This conversion will be committed one file at a time.
This NFS lock device driver was replaced by the kernel NLM around FreeBSD7 and
has not normally been used since then.
To use it, the kernel had to be built without "options NFSLOCKD" and
the nfslockd.ko had to be deleted as well.
Since it uses Giant and is no longer used, this patch removes it.
With this device driver removed, there is now a lot of unused code
in the userland rpc.lockd. That will be removed on a future commit.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D22933
Luoqi Chen reported a problem on freebsd-fs@ where a Linux NFSv4 client
was able to open and write to a file when the file's permissions were
not set to allow the owner write access.
Since NFS servers check file permissions on every write RPC, it is standard
practice to allow the owner of the file to do writes, regardless of
file permissions. This provides POSIX like behaviour, since POSIX only
checks permissions upon open(2).
The traditional way NFS clients handle this is to check access via the
Access operation/RPC and use that to determine if an open(2) on the
client is allowed.
It appears that, for NFSv4, the Linux client expects the NFSv4 Open (not a
POSIX open) operation to fail with NFSERR_ACCES if the file is not being
created and file permissions do not allow owner access, unlike NFSv3.
Since both the Linux and OpenSolaris NFSv4 servers seem to exhibit this
behaviour, this patch changes the FreeBSD NFSv4 server to do the same.
A sysctl called vfs.nfsd.v4openaccess can be set to 0 to return the
NFSv4 server to its previous behaviour.
Since both the Linux and FreeBSD NFSv4 clients seem to exhibit correct
behaviour with the access check for file owner in Open enabled, it is enabled
by default.
Reported by: luoqi.chen@gmail.com
MFC after: 2 weeks
Peter reported that his dmesg was getting cluttered with
nfsrv_cache_session: no session
messages when he rebooted his NFS server and they did not seem useful.
He was correct, in that these messages are "normal" and expected when
NFSv4.1 or NFSv4.2 are mounted and the server is rebooted.
This patch silences the printf() during the grace period after a reboot.
It also adds the client IP address to the printf(), so that the message
is more useful if/when it occurs. If this happens outside of the
server's grace period, it does indicate something is not working correctly.
Instead of adding yet another nd_XXX argument, the arguments for
nfsrv_cache_session() were simplified to take a "struct nfsrv_descript *".
Reported by: pen@lysator.liu.se
MFC after: 2 weeks
r357614 added CTLFLAG_NEEDGIANT to make it easier to find nodes that are
still not MPSAFE (or already are but aren’t properly marked).
Use it in preparation for a general review of all nodes.
This is non-functional change that adds annotations to SYSCTL_NODE and
SYSCTL_PROC nodes using one of the soon-to-be-required flags.
Mark all obvious cases as MPSAFE. All entries that haven't been marked
as MPSAFE before are by default marked as NEEDGIANT
Approved by: kib (mentor, blanket)
Commented by: kib, gallatin, melifaro
Differential Revision: https://reviews.freebsd.org/D23718
The PR reported a crash that occurred when a file was removed while
client(s) were actively doing lock operations on it.
Since nfsvno_getvp() will return NULL when the file does not exist,
the bug was obvious and easy to fix via this patch. It is a little
surprising that this wasn't found sooner, but I guess the above
case rarely occurs.
Tested by: iron.udjin@gmail.com
PR: 242768
Reported by: iron.udjin@gmail.com
MFC after: 2 weeks
The current notion of an active vnode is eliminated.
Vnodes transition between 0<->1 hold counts all the time and the
associated traversal between different lists induces significant
scalability problems in certain workloads.
Introduce a global list containing all allocated vnodes. They get
unlinked only when UMA reclaims memory and are only requeued when
hold count reaches 0.
Sample result from an incremental make -s -j 104 bzImage on tmpfs:
stock: 118.55s user 3649.73s system 7479% cpu 50.382 total
patched: 122.38s user 1780.45s system 6242% cpu 30.480 total
Reviewed by: jeff
Tested by: pho (in a larger patch, previous version)
Differential Revision: https://reviews.freebsd.org/D22997
This obviates the need to scan the entire active list looking for vnodes
of interest.
msync is handled by adding all vnodes with write count to the lazy list.
deferred inactive directly adds vnodes as it sets the VI_DEFINACT flag.
Vnodes get dequeued from the list when their hold count reaches 0.
Newly added MNT_VNODE_FOREACH_LAZY* macros support filtering so that
spurious locking is avoided in the common case.
Reviewed by: jeff
Tested by: pho (in a larger patch, previous version)
Differential Revision: https://reviews.freebsd.org/D22995
Filesystems which want to use it in limited capacity can employ the
VOP_UNLOCK_FLAGS macro.
Reviewed by: kib (previous version)
Differential Revision: https://reviews.freebsd.org/D21427
None of these case were actually using the variable(s) uninitialized, but
I figured that silencing the warnings via initializing them made sense.
Some of these predated r355677.
r355677 broke the build for the not MAC defined case and a couple of
might not be initialized warnings were generated for riscv. Others seem
to be erroneous.
Hopefully there won't be too many more build errors.
Pointy hat goes on me.
This patch adds support for NFSv4.2 (RFC-7862) and Extended Attributes
(RFC-8276) to the NFS client and server.
NFSv4.2 is comprised of several optional features that can be supported
in addition to NFSv4.1. This patch adds the following optional features:
- posix_fadvise(POSIX_FADV_WILLNEED/POSIX_FADV_DONTNEED)
- posix_fallocate()
- intra server file range copying via the copy_file_range(2) syscall
--> Avoiding data tranfer over the wire to/from the NFS client.
- lseek(SEEK_DATA/SEEK_HOLE)
- Extended attribute syscalls for "user" namespace attributes as defined
by RFC-8276.
Although this patch is fairly large, it should not affect support for
the other versions of NFS. However it does add two new sysctls that allow
a sysadmin to limit which minor versions of NFSv4 a server supports, allowing
a sysadmin to disable NFSv4.2.
Unfortunately, when the NFS stats structure was last revised, it was assumed
that there would be no additional operations added beyond what was
specified in RFC-7862. However RFC-8276 did add additional operations,
forcing the NFS stats structure to revised again. It now has extra unused
entries in all arrays, so that future extensions to NFSv4.2 can be
accomodated without revising this structure again.
A future commit will update nfsstat(1) to report counts for the new NFSv4.2
specific operations/procedures.
This patch affects the internal interface between the nfscommon, nfscl and
nfsd modules and, as such, they all must be upgraded simultaneously.
I will do a version bump (although arguably not needed), due to this.
This code has survived a "make universe" but has not been built with a
recent GCC. If you encounter build problems, please email me.
Relnotes: yes
The current vnode layout is not smp-friendly by having frequently read data
avoidably sharing cachelines with very frequently modified fields. In
particular v_iflag inspected for VI_DOOMED can be found in the same line with
v_usecount. Instead make it available in the same cacheline as the v_op, v_data
and v_type which all get read all the time.
v_type is avoidably 4 bytes while the necessary data will easily fit in 1.
Shrinking it frees up 3 bytes, 2 of which get used here to introduce a new
flag field with a new value: VIRF_DOOMED.
Reviewed by: kib, jeff
Differential Revision: https://reviews.freebsd.org/D22715
The pNFS server currently reports SpaceUsed (va_bytes) for the metadata
file. This in not correct, since the metadata file is always empty and,
as such, va_bytes is just the allocation for the empty file.
This patch adds va_bytes to the list of attributes acquired from the
DS for a file, so that it includes the allocated data size and is updated
when the file is written.
For files created on a pNFS server before this patch is applied, the
va_bytes value is estimated by rounding va_size up to a multiple of
BLKDEV_IOSIZE. Once the file is written after this patch has been
applied to the metadata server, the va_bytes returned for the file
will be correct.
This patch only affects a pNFS metadata server.
Found during testing of the NFSv4.2 pNFS server for the Allocate operation.
(Not yet in head/current.)
MFC after: 2 weeks
flag and use the same system.
This enables further fault locking improvements by allowing more faults to
proceed with a shared lock.
Reviewed by: kib
Tested by: pho
Differential Revision: https://reviews.freebsd.org/D22116
The "nd" argument for nfsrv_proxyds() is no longer used by the function.
This patch deletes it. This allows a subsequent patch to delete the "nd"
argument from nfsvno_getattr(), since it's only use of "nd" was to pass it
to nfsrv_proxyds().
Getting rid of the "nd" argument from nfsvno_getattr() avoids confusion
over why it might need "nd".
This patch is trivial and does not have any semantic effect.
The "nd" argument for nfsrv_checkdsattr() is no longer used by the function.
This patch deletes it. This allows subsequent patches to delete the "nd"
argument from nfsrv_proxyds(), since it's only use of "nd" was to pass it
to nfsrv_checkdsattr(). The same will then be true for nfsvno_getattr(),
which passes "nd" to nfsrv_proxyds().
Getting rid of the "nd" argument from nfsvno_getattr() avoids confusion
over why it might need "nd".
This patch is trivial and does not have any semantic effect.
Found by inspection while working on the NFSv4.2 server.
I do not know of an extant NFSv4.1 client that currently does a Setattr
operation for the ModeSetMasked, but it has been discussed on the linux-nfs
mailing list.
This patch adds support for doing a Setattr of ModeSetMasked, so that it
will work for any future NFSv4.1 client that chooses to do so.
Tested via a hacked FreeBSD NFSv4.1 client.
MFC after: 2 weeks
At the time of this nfsv4_sattr() call, "vp == NULL", so this patch doesn't
change the semantics, but I think it makes the code more readable.
It also makes it consistent with the nfsv4_sattr() call a few lines above
this one. Found during code inspection.
MFC after: 2 weeks
During inspection of a packet trace, I noticed that an NFSv4.0 mount
reported that it supported attributes that are only defined for NFSv4.1.
In practice, this bug appears to be benign, since NFSv4.0 clients will
not use attributes that were added for NFSv4.1.
However, this was not correct and this patch fixes the NFSv4.0 server
so that it only supports attributes defined for NFSv4.0.
It also adds a definition for NFSv4.1 attributes that can only be set,
although it is only defined as 0 for now.
This is anticipation of the addition of support for the NFSv4.1 mode+mask
attribute soon.
MFC after: 2 weeks
PR#223036 reported that INET6 callback addresses were not printed by
nfsdumpstate(8). This kernel patch adds INET6 addresses to the dump structure,
so that nfsdumpstate(8) can print them out, post-r346190.
The patch also includes the addition of #ifdef INET, INET6 as requested
by bz@.
PR: 223036
Reviewed by: bz, rgrimes
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D19839
