The existing implementations of POSIX tsearch() and tdelete() don't
attempt to perform any balancing at all. Testing reveals that inserting
100k nodes into a tree sequentially takes approximately one minute on my
system.
Though most other BSDs also don't use any balanced tree internally, C
libraries like glibc and musl do provide better implementations. glibc
uses a red-black tree and musl uses an AVL tree.
Red-black trees have the advantage over AVL trees that they only require
O(1) rotations after insertion and deletion, but have the disadvantage
that the tree has a maximum depth of 2*log2(n) instead of 1.44*log2(n).
My take is that it's better to focus on having a lower maximum depth,
for the reason that in the case of tsearch() the invocation of the
comparator likely dominates the running time.
This change replaces the tsearch() and tdelete() functions by versions
that create an AVL tree. Compared to musl's implementation, this version
is different in two different ways:
- We don't keep track of heights; just balances. This is sufficient.
This has the advantage that it reduces the number of nodes that are
being accessed. Storing heights requires us to also access all of the
siblings along the path.
- Don't use any recursion at all. We know that the tree cannot 2^64
elements in size, so the height of the tree can never be larger than
96. Use a 128-bit bitmask to keep track of the path that is computed.
This allows us to iterate over the same path twice, meaning we can
apply rotations from top to bottom.
Inserting 100k nodes into a tree now only takes 0.015 seconds. Insertion
seems to be twice as fast as glibc, whereas deletion has about the same
performance. Unlike glibc, it uses a fixed amount of memory.
I also experimented with both recursive and iterative bottom-up
implementations of the same algorithm. This iterative top-down version
performs similar to the recursive bottom-up version in terms of speed
and code size.
For some reason, the iterative bottom-up algorithm was actually 30%
faster for deletion, but has a quadratic memory complexity to keep track
of all the parent pointers.
Reviewed by: jilles
Obtained from: https://github.com/NuxiNL/cloudlibc
Differential Revision: https://reviews.freebsd.org/D4412
In r289315, I added new fields to res_state. This broke binary
backward compatibility. It also broke some ports (and possibly
other code) by requiring the definition of time_t and struct timespec.
Fix these problems by moving the new fields into __res_state_ext.
Suggested by: ume
Reviewed by: ume
MFC after: 3 days
Sponsored by: Dell Inc.
Differential Revision: https://reviews.freebsd.org/D4472
r289315 required time_t and struct timespec to be defined before
including <resolv.h>. This broke the build of net-mgmt/sx, at least.
Include <sys/timespec.h> in resolv.h to fix this with minimal pollution.
Reported by: Raphael Kubo da Costa <rakuco>
MFC after: 3 days
Sponsored by: Dell Inc.
This avoids the need for an afterinstall: hook and a check for LIBRARIES_ONLY.
It also now respects INCLUDEDIR.
This came in r249484.
Sponsored by: EMC / Isilon Storage Division
Because of how osreldate.h was being built with newvers.sh, which always
spat out a vers.c dependent on SVN or git, the meta mode build was
considering osreldate.h to depend on the current git or SVN index. This
would lead to entire tree rebuilds when modifying git's index. There's
no reason to be generating vers.c here so just skip it.
While here, in mk-osreldate.sh rename PARAM_H to proper PARAMFILE (which
newvers.sh already has a default for) and remove unneeded export.
Sponsored by: EMC / Isilon Storage Division
The _SKIP_BUILD is used while computing DIRDEPS. If MACHINE=host is passed in
then this logic was replacing 'MACHINE' with a literal value of the host arch,
which then caused the dirdeps graph to be wrong since it no longer had the
literal 'host' for any of include's dependencies.
This is a NOP currently since include/ is not usually built with MACHINE=host.
Sponsored by: EMC / Isilon Storage Division
This allows META_FILES option to be renamed META_MODE.
Also add META_COOKIE_TOUCH for use in targets that can benefit
from a cookie when in meta mode.
Differential Revision: https://reviews.freebsd.org/D4153
Reviewed by: bdrewery
On each resolver query, use stat(2) to see if the modification time
of /etc/resolv.conf has changed. If so, reload the file and reinitialize
the resolver library. However, only call stat(2) if at least two seconds
have passed since the last call to stat(2), since calling it on every
query could kill performance.
This new behavior is enabled by default. Add a "reload-period" option
to disable it or change the period of the test.
Document this behavior and option in resolv.conf(5).
Polish the man page just enough to appease igor.
https://lists.freebsd.org/pipermail/freebsd-arch/2015-October/017342.html
Reviewed by: kp, wblock
Discussed with: jilles, imp, alfred
MFC after: 1 month
Relnotes: yes
Sponsored by: Dell Inc.
Differential Revision: https://reviews.freebsd.org/D3867
FreeBSD extended ctypes to include numbers (e.g. isnumber()) but never
actually implemented it. The isnumber() function was equivalent to the
isdigit() function in every case.
Now that DragonFly's ctype source files have number definitions, the
number ctype can finally be implemented. It's given a new flag _CTYPE_N.
The isalnum() and iswalnum() functions have been changed to use this
flag rather than the _CTYPE_D digit flag.
While isalnum(), isnumber(), and their wide equivalents now return
different values in locale cases, the ishexnumber() and iswhexnumber()
functions are unchanged. They are still aliases for isxdigit() and
iswxdigit().
Also change ctype.h for isdigit and isxdigit to use sbistype like the
other functions.
Obtained from: dragonfly
If the command to be ran changes then a rebuild is caused. Checking
exists(${DESTDIR}...) from make results in this on the 2nd and
possibly subsequent builds due to staging during build. Avoid this
by always running the existence check in the make sh command.
Sponsored by: EMC / Isilon Storage Division
- Use _Bool rather than bool to resolve missing type errors in malloc_np.h.
- Fix malloc manual page #include documentation.
- Add *allocm manual pages to obsolete files.
Submitted by: jbeich
Start using the gcc sentinel attribute, which can be used to
mark varargs function that need a NULL pointer to mark argument
termination, like execl(3).
Relnotes: yes
This function is equivalent to fclose(3) function except that it
does not close the underlying file descriptor.
fdclose(3) is step forward to make FILE structure private.
Reviewed by: wblock, jilles, jhb, pjd
Approved by: pjd (mentor)
Differential Revision: https://reviews.freebsd.org/D2697
Off by default, build behaves normally.
WITH_META_MODE we get auto objdir creation, the ability to
start build from anywhere in the tree.
Still need to add real targets under targets/ to build packages.
Differential Revision: D2796
Reviewed by: brooks imp
This lets the compiler know about the alignment of pointers returned
by aligned_alloc(3), posix_memalign(3). and contigmalloc(9)
Currently this is only supported in recent gcc but we are ready to
use it if clang implements it.
Relnotes: yes
Add a manpage for it, assign the copyright to the OpenBSD project on it since it
is mostly copy/paste from OpenBSD manpage.
style(9) fixes
Differential Revision: https://reviews.freebsd.org/D2420
Reviewed by: kib
discontinued by its initial authors. In FreeBSD the code was already
slightly edited during the pf(4) SMP project. It is about to be edited
more in the projects/ifnet. Moving out of contrib also allows to remove
several hacks to the make glue.
Reviewed by: net@
The `nonnull' attribute specifies that some function parameters should be
non-null pointers. This is very useful as it helps the compiler generate
warnings on suspicious code and can also enable some small optimizations.
Also start using 'alloc_size' attribute in the allocator functions.
This is an initial step to better integrate our libc with the compiler:
these attributes are fully supported by clang and they are also useful
for the static analyzer.
Note that due to some bogus internal procedure in the way gcc ports
are built they may require updating if they were built before r280801.
Relnotes: yes
Hinted by: Android's bionic libc
Differential Revision: https://reviews.freebsd.org/D2107
GCC is still carries an old version of cdefs.h which doesn't
accept multiple parameters for the nonnull attribute.
Since this issue probably affects many ports in the tree
we will revert it for now until gcc gets fixed.
The `nonnull' attribute specifies that some function parameters should be
non-null pointers. This is very useful as it helps the compiler generate
warnings on suspicious code and can also enable some small optimizations.
In clang this is also useful for the static analyzer.
While we could go on defining this all over the tree, it only
makes sense to annotate a subset of critical functions.
Hinted by: Android's bionic libc
Differential Revision: https://reviews.freebsd.org/D2101
- bootparamd
- bootpd
- finger/fingerd
- ftp/ftpd
- hastctl/hastd
- iscsid, et al
- rbootd
- talk/talkd
- tcpd, et al
- tftp/tftpd
Add src.conf entries for the various components and do a best effort
at adding components to tools/build/mk/OptionalObsoleteFiles.inc
in a separate word from the _count. This does not permit both items to
be updated atomically in a portable manner. As a result, sem_post()
must always perform a system call to safely clear _has_waiters.
This change removes the _has_waiters field and instead uses the high bit
of _count as the _has_waiters flag. A new umtx object type (_usem2) and
two new umtx operations are added (SEM_WAIT2 and SEM_WAKE2) to implement
these semantics. The older operations are still supported under the
COMPAT_FREEBSD9/10 options. The POSIX semaphore API in libc has
been updated to use the new implementation. Note that the new
implementation is not compatible with the previous implementation.
However, this only affects static binaries (which cannot be helped by
symbol versioning). Binaries using a dynamic libc will continue to work
fine. SEM_MAGIC has been bumped so that mismatched binaries will error
rather than corrupting a shared semaphore. In addition, a padding field
has been added to sem_t so that it remains the same size.
Differential Revision: https://reviews.freebsd.org/D961
Reported by: adrian
Reviewed by: kib, jilles (earlier version)
Sponsored by: Norse
In some cases, TSC is broken and special applications might benefit
from memory mapping HPET and reading the registers to count time.
Most often the main HPET counter is 32-bit only[1], so this only gives
the application a 300 second window based on the default HPET
interval.
Other applications, such as Intel's DPDK, expect /dev/hpet to be
present and use it to count time as well.
Although we have an almost userland version of gettimeofday() which
uses rdtsc in userland, it's not always possible to use it, depending
on how broken the multi-socket hardware is.
Install the acpi_hpet.h so that applications can use the HPET register
definitions.
[1] I haven't found a system where HPET's main counter uses more than
32 bit. There seems to be a discrepancy in the Intel documentation
(claiming it's a 64-bit counter) and the actual implementation (a
32-bit counter in a 64-bit memory area).
MFC after: 1 week
Relnotes: yes
I've looked at the GCC sources and I now understand what's going wrong.
THe C11 keywords are simply nonexistent when using C++ mode. They are
marked as C-only in the parser. This is absolutely impractical for
multiple reasons:
- The C11 keywords do not conflict with C++ naming rules. They all start
with _[A-Z]. There is no reason to make them C-only.
- It makes it practically impossible for people to use these keywords in
C header files and expect them to work from within C++ sources.
As I said in my previous commit message: GCC is by far the weirdest
compiler that I've ever used.
As GCC also gained support for the C11 keywords over time, we can patch
up <sys/cdefs.h> to not define these anymore. This has the advantage
that error messages for static assertions are printed natively and that
_Alignas() will work with even a type outside of C11 mode.
All C11 keywords are supported with GCC 4.7 and higher, with the
exception of _Thread_local and _Generic. These are only supported as of
GCC 4.9.
bsearch_b is the Apple blocks enabled version of bsearch(3).
This was added to libc in Revision 264042 but the commit
missed the declaration required to make use of it.
While here move some other block-related functions to the
BSD_VISIBLE block as these are non-standard.
Phabric: D638
Reviewed by: theraven, wollman
This change extends all of the functions present in the <pthread.h> and
<threads.h> headers to have lock annotations. This will allow Clang to
warn about the following:
- Locking a function twice,
- Unlocking a function without a mutex being locked,
- Forgetting to unlock a mutex before returning,
- Destroying or reinitializing a mutex that is currenty locked,
- Using an unlocked mutex in combination with a condition variable.
Enabling these annotations already allowed me to catch a bug in one of
our userspace tools (r270749).
Back in 2011 obrien has added the #define macro in sys/sys/stddef.h to
guard ptrdiff_t. Add similar protection to the identical code in
include/stddef.h.
Submitted by: Mariusz Zaborski <oshogbo@FreeBSD.org>
MFC after: 1 week
From
http://www.isc.org/downloads/libbind/
The libbind functions have been separated from the BIND suite as of BIND
9.6.0. Originally from older versions of BIND, they have been continually
maintained and improved but not installed by default with BIND 9. This
standard resolver library contains the same historical functions and
headers included with many Unix operating systems. In fact, most
implementations are based on the same original code.
At present, NetBSD maintains libbind code, now known as "netresolv".
While testing this I found a conformance issue in hdestroy()
that will be fixed in a subsequent commit.
Obtained from: NetBSD (hcreate.c, CVS Rev. 1.7)
The current ordering of this header is a feature as it
is more consistent with POSIX.
Also adding gratuitous newlines is not elegant.
Pointed out by: bde
- In the unionfs case, opendir() and fdopendir() read the directory's full
contents and cache it. This cache is not refreshed when rewinddir() is
called, so rewinddir() will not notice updates to a directory. Fix this
by splitting the code to fetch a directory's contents out of
__opendir_common() into a new _filldir() function and call this from
rewinddir() when operating on a unionfs directory.
- If rewinddir() is called on a directory opened with fdopendir() before
any directory entries are fetched, rewinddir() will not adjust the seek
location of the backing file descriptor. If the file descriptor passed
to fdopendir() had a non-zero offset, the rewinddir() will not rewind to
the beginning. Fix this by always seeking back to 0 in rewinddir().
This means the dd_rewind hack can also be removed.
While here, add missing locking to rewinddir().
CR: https://phabric.freebsd.org/D312
Reviewed by: jilles
MFC after: 1 week
POSIX.1-2008 specifies that those two functions should be declared by
including <strings.h>, not <string.h> (the latter only has strcoll_l()
and strxfrm_l()):
http://pubs.opengroup.org/onlinepubs/9699919799/functions/strcasecmp.html
Obtained from: DragonFlyBSD
Reviewed by: theraven
MFC after: 2 weeks
The CUSE library is a wrapper for the devfs kernel functionality which
is exposed through /dev/cuse . In order to function the CUSE kernel
code must either be enabled in the kernel configuration file or loaded
separately as a module. Currently none of the committed items are
connected to the default builds, except for installing the needed
header files. The CUSE code will be connected to the default world and
kernel builds in a follow-up commit.
The CUSE module was written by Hans Petter Selasky, somewhat inspired
by similar functionality found in FUSE. The CUSE library can be used
for many purposes. Currently CUSE is used when running Linux kernel
drivers in user-space, which need to create a character device node to
communicate with its applications. CUSE has full support for almost
all devfs functionality found in the kernel:
- kevents
- read
- write
- ioctl
- poll
- open
- close
- mmap
- private per file handle data
Requested by several people. Also see "multimedia/cuse4bsd-kmod" in
ports.
or __POSIX_VISIBLE.
Whenever <sys/cdefs.h> sets __BSD_VISIBLE to non-zero, it also sets
__POSIX_VISIBLE and __XSI_VISIBLE to the newest version supported.
No functional change is intended.
AppleTalk was a network transport protocol for Apple Macintosh devices
in 80s and then 90s. Starting with Mac OS X in 2000 the AppleTalk was
a legacy protocol and primary networking protocol is TCP/IP. The last
Mac OS X release to support AppleTalk happened in 2009. The same year
routing equipment vendors (namely Cisco) end their support.
Thus, AppleTalk won't be supported in FreeBSD 11.0-RELEASE.
IPX was a network transport protocol in Novell's NetWare network operating
system from late 80s and then 90s. The NetWare itself switched to TCP/IP
as default transport in 1998. Later, in this century the Novell Open
Enterprise Server became successor of Novell NetWare. The last release
that claimed to still support IPX was OES 2 in 2007. Routing equipment
vendors (e.g. Cisco) discontinued support for IPX in 2011.
Thus, IPX won't be supported in FreeBSD 11.0-RELEASE.
device is an active kernel console and "off" otherwise. This is designed to
allow serial-booting x86 systems to provide a login prompt on the serial line
by default without providing one on all systems by default.
Comments and suggestions by: grehan, dteske, jilles
MFC after: 1 month
3-clause BSD license as specified by Oracle America, Inc. in 2010.
This license change was approved by Wim Coekaerts, Senior Vice
President, Linux and Virtualization at Oracle Corporation.
when there is an invalid character in the output codeset while it is
valid in the input. However, POSIX requires iconv() to perform an
implementation-defined conversion on the character. So, Citrus iconv converts
such a character to a special character which means it is invalid in the
output codeset.
This is not a problem in most cases but some software like libxml2 depends
on GNU's behavior to determine if a character is output as-is or another form
such as a character entity (&#NNN;).
FreeBSD systems usually implemented this as a third party module and
our implementation hasn't played as nicely with the old way as it could
have.
To that end:
* Rename the iconv* symbols in libc.so.7 to have a __bsd_ prefix.
* Provide .symver compatability with existing 10.x+ binaries that
referenced the iconv symbols. All existing binaries should work.
* Like on Linux/glibc systems, add a libc_nonshared.a to the ldscript
at /usr/lib/libc.so.
* Move the "iconv*" wrapper symbols to libc_nonshared.a
This should solve the runtime ambiguity about which symbols resolve
to where. If you compile against the iconv in libc, your runtime
dependencies will be unambiguous.
Old 9.x libraries and binaries will always resolve against their
libiconv.so.3 like they did on 9.x. They won't resolve against libc.
Old 10.x binaries will be satisified by the .symver helpers.
This should allow ports to selectively compile against the libiconv
port if needed and it should behave without ambiguity now.
Discussed with: kib
good. This caused libc to spoof the ports libiconv namespace and
provide a colliding libiconv.so.3 to fool rtld. This should have
been removed some time ago.
in net, to avoid compatibility breakage for no sake.
The future plan is to split most of non-kernel parts of
pfvar.h into pf.h, and then make pfvar.h a kernel only
include breaking compatibility.
Discussed with: bz
newvers.sh. Pass it in from include/Makefile. If it isn't passed in,
fall back to the old logic of using dirname $0.
Using dirname $0 does not yield the path to the script if it was
sourced in from another script in another directory; you end up with
the parent script's path. That was causing newvers.sh to look one
level below the FreeBSD src/ directory when building osreldate.h and it
may find something like a git or svn repo there that has nothing to do
with FreeBSD.
PR: 174422
Approved by: re ()
MFC after: 2 weeks
This would cause detection of old versions of SVN to cause fatal errors
instead of being caught and handled, which would make the build fail if
the tree had been checked out with an older version of SVN (e.g. 1.6).
Discussed with: gjb
Approved by: re (marius)
may come in from the environment and reflect the user's interactive shell.
Using bare "sh" is the dominant pattern in existing makefiles.
MFC this together with r255775.
Approved by: re ()
MFC after: 2 weeks
than launching the script directly and relying on #! to launch the shell.
This avoids problems when the source is mounted with the noexec flag.
MFC this together with r255775.
Approved by: re (kib)
MFC after: 2 weeks
newvers.sh into a temporary subshell with inline make rules.
Using a separate script fixes a variety of problems, including establishing
the correct dependencies in the makefiles. It also eliminates a problem
with the way newvers.sh uses `realpath $0`, because $0 expands differently
within a script sourced into a rule in a makefile depending on the version
of make and of /bin/sh being used. The latter can cause build breakage in a
cross-build environment, and can also make it difficult to compile 10.0 on
older pre-10.0 systems.
PR: 160646 174422
Submitted by: Garrett Cooper <yaneurabeya@gmail.com>
Approved by: re (gjb)
MFC after: 2 weeks
hrs@ provided this verison of the patch and showed me where all the needed
changes were to be made outside of gpioctl.c
Approved by: re (hrs)
MFC after: 2 weeks
function, but returns directory file descriptor instead of closing it.
Submitted by: Mariusz Zaborski <oshogbo@FreeBSD.org>
Sponsored by: Google Summer of Code 2013
I removed functionality not proposed for POSIX in Austin group issue #411.
A man page (my own) and test cases will follow in later commits.
PR: 176233
Submitted by: Jukka Ukkonen
extensions and also tried to be link time compatible with ports libiconv.
This splits that functionality and enables the parts that shouldn't
interfere with the port by default.
WITH_ICONV (now on by default) - adds iconv.h, iconv_open(3) etc.
WITH_LIBICONV_COMPAT (off by default) adds the libiconv_open etc API, linker
symbols and even a stub libiconv.so.3 that are good enough to be able
to 'pkg delete -f libiconv' on a running system and reasonably expect it
to work.
I have tortured many machines over the last few days to try and reduce
the possibilities of foot-shooting as much as I can. I've successfully
recompiled to enable and disable the libiconv_compat modes, ports that use
libiconv alongside system iconv etc. If you don't enable the
WITH_LIBICONV_COMPAT switch, they don't share symbol space.
This is an extension of behavior on other system. iconv(3) is a standard
libc interface and libiconv port expects to be able to run alongside it on
systems that have it.
Bumped osreldate.
but ACM formula we use have internal state (and return value) in the
[1, 0x7ffffffe] range, so our RAND_MAX (0x7fffffff) is never reached
because it is off by one, zero is not reached too.
Correct both RAND_MAX and rand(3) return value, shifting last one
to the 0 by 1 subtracted, resulting POSIXed [0, 0x7ffffffd(=new RAND_MAX)]
range.
2) Add a checks for not overflowing on too big seeds. It may happens on
the machines, where sizeof(unsigned int) > 32 bits.
Reviewed by: bde [1]
MFC after: 2 weeks
a macro with parameters. Remove a __DECONST hack and add consts instead
for gnu libiconv API compatability. This makes it work with things like
devel/boost-libs that expects to use "iconv" as though it were a pointer.
- Reconnect with some minor modifications, in particular now selsocket()
internals are adapted to use sbintime units after recent'ish calloutng
switch.
device names "md" or "md[0-9]*" and a "file" option are specified in
/etc/fstab like this:
md none swap sw,file=/swap.bin 0 0
- Add GBDE/GELI encrypted swap space specification support, which
rc.d/encswap supported. The /etc/fstab lines are like the following:
/dev/ada1p1.bde none swap sw 0 0
/dev/ada1p2.eli none swap sw 0 0
.eli devices accepts aalgo, ealgo, keylen, and sectorsize as options.
swapctl(8) can understand an encrypted device in the command line
like this:
# swapctl -a /dev/ada2p1.bde
- "-L" flag is added to support "late" option to defer swapon until
rc.d/mountlate runs.
- rc.d script change:
rc.d/encswap -> removed
rc.d/addswap -> just display a warning message if $swapfile is defined
rc.d/swap1 -> renamed to rc.d/swap
rc.d/swaplate -> newly added to support "late" option
These changes alleviate a race condition between device creation/removal
and swapon/swapoff.
MFC after: 1 week
Reviewed by: wblock (manual page)
implementations visible for use by applications. The functions $F that
are now weak symbols are:
allocm, calloc, dallocm, free, malloc, malloc_usable_size,
nallocm, posix_memalign, rallocm, realloc, sallocm
The non-weak implementations of $F are exported as __$F.
Submitted by: stevek@juniper.net
Reviewed by: jasone@, kib@
Approved by: jasone@ (jemalloc)
Obtained from: juniper Networks, Inc
It turns out that in C++11, char16_t and char32_t are built-in types;
language keywords. Just fix this by putting traditional _*_T_DECLARED
blocks around the definitions. We'll just predefine these in
<sys/_types.h>.
This also opens up the possibility to define char16_t in other header
files, if ever needed (e.g. if we would gain a <ctype.h> for
char16_t/char32_t).
The <uchar.h> header, part of C11, adds a small number of utility
functions for 16/32-bit "universal" characters, which may or may not be
UTF-16/32. As our wchar_t is already ISO 10646, simply add light-weight
wrappers around wcrtomb() and mbrtowc().
While there, also add (non-yet-standard) _l functions, similar to the
ones we already have for the other locale-dependent functions.
Reviewed by: theraven
The pipe2() function is similar to pipe() but allows setting FD_CLOEXEC and
O_NONBLOCK (on both sides) as part of the function.
If p points to two writable ints, pipe2(p, 0) is equivalent to pipe(p).
If the pointer is not valid, behaviour differs: pipe2() writes into the
array from the kernel like socketpair() does, while pipe() writes into the
array from an architecture-specific assembler wrapper.
Reviewed by: kan, kib
By using __has_extension(c_generic_selections), we can explicitly test
whether we're dealing with a version of Clang that supports _Generic().
That way we can use the improved <tgmath.h> code, even when not using
-std=c11. This massively reduces the compilation time when invoking
these functions.
This theoretically allows a compiler to optimize (parts of) the array
away if unused.
While there, make the array size implicit and use a _Static_assert() to
ensure that the definition matches up with the number of elements in the
list.
routines provide write-only stdio FILE objects that store their data in a
dynamically allocated buffer. They are a string builder interface somewhat
akin to a completely dynamic sbuf.
Reviewed by: bde, jilles (earlier versions)
MFC after: 1 month
