Commit Graph

2273 Commits

Author SHA1 Message Date
Ed Schouten
18528470cb Make blocking CloudABI futex operations work.
Blocking on locks and condition variables can be accomplished by polling
and using the special filters CONDVAR, LOCK_RDLOCK and LOCK_WRLOCK.

For now it wouldn't make sense to implement this functionality into
kqueue() itself, for the reason that they are CloudABI specific and
would require us to resize 'struct kevent' to hold all of the parameters
of interest.

Add a bandaid to the CloudABI poll system call to call into the futex
code directly if it detects specific combinations of events that are
used by the C library.

Obtained from:	https://github.com/NuxiNL/freebsd
2015-08-12 08:41:48 +00:00
Ed Schouten
322e16e87e Make poll() and kqueue() on CloudABI work.
This change implements two functions, cloudabi64_kevent_copyin() and
cloudabi64_kevent_copyout(), that convert CloudABI structures to
FreeBSD's struct kevent. CloudABI uses two structures: subscription_t
and event_t. The former is used for input, whereas the latter is used
for output. Unlike struct kevent, fields aren't overloaded for multiple
purposes or for separate event types.

For poll() we call into the newly introduced kern_kevent_anonymous()
function that allows us to poll without a file descriptor. This function
is not only used by poll(), but also by functions such as
sleep() and clock_nanosleep().

Reviewed by:	jmg
Obtained from:	https://github.com/NuxiNL/freebsd
Differential Revision:	https://reviews.freebsd.org/D3308
2015-08-12 07:59:00 +00:00
Ed Schouten
55a224afa2 Fall back to O_RDONLY -- not O_WRONLY.
If CloudABI processes open files with a set of requested rights that do
not match any of the privileges granted by O_RDONLY, O_WRONLY or O_RDWR,
we'd better fall back to O_RDONLY -- not O_WRONLY.
2015-08-11 14:08:46 +00:00
Ed Schouten
9d9123a80d Properly convert the error number to CloudABI's indexing.
We currently return FreeBSD's errno value directly, which is of course
not correct.
2015-08-11 14:07:04 +00:00
Ed Schouten
65c17fe451 Make cap_rights_limit() work for CloudABI processes.
Call into the recently introduced kern_cap_rights_limit() function to
restrict rights.
2015-08-11 08:44:19 +00:00
Ed Schouten
0f85ff377b Add file_open(): the underlying system call of openat().
CloudABI purely operates on file descriptor rights (CAP_*). File
descriptor access modes (O_ACCMODE) are emulated on top of rights.

Instead of accepting the traditional flags argument, file_open() copies
in an fdstat_t object that contains the initial rights the descriptor
should have, but also file descriptor flags that should persist after
opening (APPEND, NONBLOCK, *SYNC). Only flags that don't persist (EXCL,
TRUNC, CREAT, DIRECTORY) are passed in as an argument.

file_open() first converts the rights, the persistent flags and the
non-persistent flags to fflags. It then calls into vn_open(). If
successful, it installs the file descriptor with the requested
rights, trimming off rights that don't apply to the type of
the file that has been opened.

Unlike kern_openat(), this function does not support /dev/fd/*. I can't
think of a reason why we need to support this for CloudABI.

Obtained from:	https://github.com/NuxiNL/freebsd
Differential Revision:	https://reviews.freebsd.org/D3235
2015-08-06 06:47:28 +00:00
Ed Schouten
aaf53ab2aa Correct the previous commit: remove the DECLARE_MODULE().
It looks like a MODULE_VERSION() can also appear on its own -- there is
no need to use explicitly use DECLARE_MODULE(). Looking at other
modules, this seems common practice.
2015-08-05 16:53:49 +00:00
Ed Schouten
b6efa27589 Add DECLARE_MODULE() to the "cloudabi" kernel module.
This kernel module does not require any explicit initialization, but a
module declaration is needed to let the "cloudabi64" kernel module
automatically pull this in.

Obtained from:	https://github.com/NuxiNL/freebsd
2015-08-05 16:45:47 +00:00
Ed Schouten
36310bcd1d Make fcntl(F_SETFL) work.
The stat_put() system call can be used to modify file descriptor
attributes, such as flags, but also Capsicum permission bits. Support
for changing Capsicum bits will be added as soon as its dependent
changes have been pushed through code review.

Obtained from:	https://github.com/NuxiNL/freebsd
2015-08-05 16:15:43 +00:00
Ed Schouten
2412ae2b8e Regenerate the system call table. 2015-08-05 13:10:13 +00:00
Ed Schouten
2837d9ed43 Import the latest CloudABI system call definitions and table.
We're going to need these for next code I'm going to send out for
review: support for poll() and kqueue() on CloudABI.
2015-08-05 13:09:46 +00:00
Ed Schouten
db1c8ee585 Add the remaining pointer size independent CloudABI socket system calls.
CloudABI uses a structure called cloudabi_sockstat_t. Think of it as
'struct stat' for sockets. It is used by functions such as
getsockname(), getpeername(), some of the getsockopt() values, etc.

This change implements the sock_stat_get() system call that returns a
copy of this structure. The accept() system call should also return a
full copy of this structure eventually, but for now we're only
interested in the peer address. Add a TODO() to make sure this is
patched up later on.

Differential Revision:	https://reviews.freebsd.org/D3218
2015-08-05 08:18:05 +00:00
Ed Schouten
4958fab8cd Allow the creation of polling descriptors (kqueues) on CloudABI. 2015-08-05 07:37:06 +00:00
Ed Schouten
a2034cc98a Allow the creation of kqueues with a restricted set of Capsicum rights.
On CloudABI we want to create file descriptors with just the minimal set
of Capsicum rights in place. The reason for this is that it makes it
easier to obtain uniform behaviour across different operating systems.

By explicitly whitelisting the operations, we can return consistent
error codes, but also prevent applications from depending OS-specific
behaviour.

Extend kern_kqueue() to take an additional struct filecaps that is
passed on to falloc_caps(). Update the existing consumers to pass in
NULL.

Differential Revision:	https://reviews.freebsd.org/D3259
2015-08-05 07:36:50 +00:00
Ed Schouten
0c0964844e Let the CloudABI futex code use umtx_keys.
The CloudABI kernel still passes all of the cloudlibc unit tests.

Reviewed by:	vangyzen
Differential Revision:	https://reviews.freebsd.org/D3286
2015-08-04 06:02:03 +00:00
Ed Schouten
f52c3dd415 Allow CloudABI processes to create shared memory objects.
Summary:
Use the newly created `kern_shm_open()` function to create objects with
just the rights that are actually needed.

Reviewers: jhb, kib

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3260
2015-08-01 07:51:48 +00:00
Ed Schouten
367a13f905 Limit rights on process descriptors.
On CloudABI, the rights bits returned by cap_rights_get() match up with
the operations that you can actually perform on the file descriptor.

Limiting the rights is good, because it makes it easier to get uniform
behaviour across different operating systems. If process descriptors on
FreeBSD would suddenly gain support for any new file operation, this
wouldn't become exposed to CloudABI processes without first extending
the rights.

Extend fork1() to gain a 'struct filecaps' argument that allows you to
construct process descriptors with custom rights. Use this in
cloudabi_sys_proc_fork() to limit the rights to just fstat() and
pdwait().

Obtained from:	https://github.com/NuxiNL/freebsd
2015-07-31 10:21:58 +00:00
Ed Schouten
8328babdd0 Make pipes in CloudABI work.
Summary:
Pipes in CloudABI are unidirectional. The reason for this is that
CloudABI attempts to provide a uniform runtime environment across
different flavours of UNIX.

Instead of implementing a custom pipe that is unidirectional, we can
simply reuse Capsicum permission bits to support this. This is nice,
because CloudABI already attempts to restrict permission bits to
correspond with the operations that apply to a certain file descriptor.

Replace kern_pipe() and kern_pipe2() by a single kern_pipe() that takes
a pair of filecaps. These filecaps are passed to the newly introduced
falloc_caps() function that creates the descriptors with rights in
place.

Test Plan:
CloudABI pipes seem to be created with proper rights in place:

https://github.com/NuxiNL/cloudlibc/blob/master/src/libc/unistd/pipe_test.c#L44

Reviewers: jilles, mjg

Reviewed By: mjg

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3236
2015-07-29 17:18:27 +00:00
Ed Schouten
9d2332c9ee Split up Capsicum to CloudABI rights conversion into two separate routines.
CloudABI's openat() ensures that files are opened with the smallest set
of relevant rights. For example, when opening a FIFO, unrelated rights
like CAP_RECV are automatically removed. To remove unrelated rights, we
can just reuse the code for this that was already present in the rights
conversion function.
2015-07-29 12:42:45 +00:00
Ed Schouten
3720b82fa8 Implement CloudABI's readdir().
Summary:
CloudABI's readdir() system call could be thought of as a mixture
between FreeBSD's getdents(2) and pread(). Instead of using the file
descriptor offset, userspace provides a 64-bit cloudabi_dircookie_t
continue reading at a given point. CLOUDABI_DIRCOOKIE_START, having
value 0, can be used to return entries at the start of the directory.

The file descriptor offset is not used to store the cookie for the
reason that in a file descriptor centric environment, it would make
sense to allow concurrent use of a single file descriptor.

The remaining space returned by the system call should be filled with a
partially truncated copy of the next entry. The advantage of doing this
is that it gracefully deals with long filenames. If the C library
provides a buffer that is too small to hold a single entry, it can still
extract the directory entry header, meaning that it can retry the read
with a larger buffer or skip it using the cookie.

Test Plan:
This implementation passes the cloudlibc unit tests at:

	https://github.com/NuxiNL/cloudlibc/tree/master/src/libc/dirent

Reviewers: marcel, kib

Reviewed By: kib

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3226
2015-07-29 06:31:44 +00:00
Ed Schouten
1d96fd8d9f Implement file attribute modification system calls for CloudABI.
CloudABI uses a system call interface to modify file attributes that is
more similar to KPI's/FUSE, namely where a stat structure is passed back
to the kernel, together with a bitmask of attributes that should be
changed. This would allow us to update any set of attributes atomically.

That said, I'd rather not go as far as to actually implement it that
way, as it would require us to duplicate more code than strictly needed.
Let's just stick to the combinations that are actually used by
cloudlibc.

Obtained from:	https://github.com/NuxiNL/freebsd
2015-07-28 12:57:19 +00:00
Ed Schouten
29515a68a5 Implement directory and FIFO creation.
The file_create() system call can be used to create files of a given
type. Right now it can only be used to create directories and FIFOs. As
CloudABI does not expose filesystem permissions, this system call lacks
a mode argument. Simply use 0777 or 0666 depending on the file type.
2015-07-28 06:50:47 +00:00
Ed Schouten
cec575201a Make fstat() and friends work.
Summary:
CloudABI provides access to two different stat structures:

- fdstat, containing file descriptor level status: oflags, file
  descriptor type and Capsicum rights, used by cap_rights_get(),
  fcntl(F_GETFL), getsockopt(SO_TYPE).
- filestat, containing your regular file status: timestamps, inode
  number, used by fstat().

Unlike FreeBSD's stat::st_mode, CloudABI file descriptor types don't
have overloaded meanings (e.g., returning S_ISCHR() for kqueues). Add a
utility function to extract the type of a file descriptor accurately.

CloudABI does not work with O_ACCMODEs. File descriptors have two sets
of Capsicum-style rights: rights that apply to the file descriptor
itself ('base') and rights that apply to any new file descriptors
yielded through openat() ('inheriting'). Though not perfect, we can
pretty safely decompose Capsicum rights to such a pair. This is done in
convert_capabilities().

Test Plan: Tests for these system calls are fairly extensive in cloudlibc.

Reviewers: jonathan, mjg, #manpages

Reviewed By: mjg

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3171
2015-07-28 06:36:49 +00:00
Ed Schouten
af7e75f59d Add a futex implementation for CloudABI.
Summary:
CloudABI provides two different types of futex objects: read-write locks
and condition variables. There is no need to provide separate support
for once objects and thread joining, as these are efficiently simulated
by blocking on a read-write lock. Mutexes simply use read-write locks.

Condition variables always have a lock object associated to them. They
always know to which lock a thread needs to be migrated if woken up.
This allows us to implement requeueing. A broadcast on a condition
variable will never cause multiple threads to be woken up at once. They
will be woken up iteratively.

This implementation still has lots of room for improvement. Locking is
coarse and right now we use linked lists to store all of the locks and
condition variables, instead of using a hash table. The primary goal of
this implementation was to behave correctly. Performance will be
improved as we go.

Test Plan:
This futex implementation has been in use for the last couple of months
and seems to work pretty well. All of the cloudlibc and libc++ unit
tests seem to pass.

Reviewers: dchagin, kib, vangyzen

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3148
2015-07-27 10:07:29 +00:00
Ed Schouten
533c8a29da Regenerate system call table. 2015-07-27 10:04:28 +00:00
Ed Schouten
f4c06d124f Sync in latest upstream system call definitions.
Futex object scopes have been renamed from using their own constants to
simply reusing the existing CLOUDABI_MAP_{PRIVATE,SHARED} flags, as they
are more accurate in this context.
2015-07-27 10:04:06 +00:00
Ed Schouten
4615998165 Implement the basic system calls that operate on pathnames.
Summary:
Unlike FreeBSD, CloudABI does not use null terminated strings for its
pathnames. Introduce a function called copyin_path() that can be used by
all of the filesystem system calls that use pathnames. This change
already implements the system calls that don't depend on any additional
functionality (e.g., conversion of struct stat).

Also implement the socket system calls that operate on pathnames, namely
the ones used by the C library functions bindat() and connectat(). These
don't receive a 'struct sockaddr_un', but just the pathname, meaning
they could be implemented in such a way that they don't depend on the
size of sun_path. For now, just use the existing interfaces.

Add a missing #include to cloudabi_syscalldefs.h to get this code to
build, as one of its macros depends on UINT64_C().

Test Plan:
These implementations have already been tested in the CloudABI branch on
GitHub. They pass all of the tests.

Reviewers: kib, pjd

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3097
2015-07-24 07:46:02 +00:00
Ed Schouten
fef97e09d9 Allow us to create UNIX sockets and socketpairs in CloudABI processes. 2015-07-23 13:52:53 +00:00
Ed Schouten
c989441af6 Regenerate system call table. 2015-07-22 10:05:46 +00:00
Ed Schouten
73dcd7db56 Import upstream changes to the system call definitions.
Support has been added for providing the scope of a futex operation,
whether the futex is local to the process or shared between processes.
2015-07-22 10:04:53 +00:00
Ed Schouten
072cb63ddc Make clock_gettime() and clock_getres() work for CloudABI programs.
Though the standard C library uses a 'struct timespec' using a 64-bit
'time_t', there is no need to use such a type at the system call level.
CloudABI uses a simple 64-bit unsigned timestamp in nanoseconds. This is
sufficient to express any time value from 1970 to 2554.

The CloudABI low-level interface also supports fetching timestamp values
with a lower precision. Instead of overloading the clock ID argument for
this purpose, the system call provides a precision argument that may be
used to specify the maximum slack. The current system call
implementation does not use this information, but it's good to already
have this available.

Expose cloudabi_convert_timespec(), as we're going to need this for
fstat() as well.

Obtained from:	https://github.com/NuxiNL/freebsd
2015-07-21 15:08:13 +00:00
Ed Schouten
21d30b29d5 Make thread creation work for CloudABI processes.
Summary:
Remove the stub system call that was put in place during the system call
import and replace it by a target-dependent version stored in sys/amd64.
Initialize the thread in a way similar to cpu_set_upcall_kse(). We
provide the entry point with two arguments: the thread ID and the
argument pointer.

Test Plan:
Thread creation still seems to work, both for FreeBSD and CloudABI
binaries.

Reviewers: dchagin, mjg, kib

Reviewed By: kib

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3110
2015-07-21 12:47:15 +00:00
Ed Schouten
62c31cffae Make forking of CloudABI processes work.
Just like FreeBSD+Capsicum, CloudABI uses process descriptors. Return
the file descriptor number to the parent process.

To the child process we both return a special value for the file
descriptor number (CLOUDABI_PROCESS_CHILD). We also return the thread ID
of the new thread in the copied process, so the threading library can
reinitialize itself.

Obtained from:	https://github.com/NuxiNL/freebsd
2015-07-20 13:46:22 +00:00
Marcelo Araujo
f19e47d691 Add support to the jail framework to be able to mount linsysfs(5) and
linprocfs(5).

Differential Revision:	D2846
Submitted by:		Nikolai Lifanov <lifanov@mail.lifanov.com>
Reviewed by:		jamie
2015-07-19 08:52:35 +00:00
Konstantin Belousov
b4490c6e93 The si_status field of the siginfo_t, provided by the waitid(2) and
SIGCHLD signal, should keep full 32 bits of the status passed to the
_exit(2).

Split the combined p_xstat of the struct proc into the separate exit
status p_xexit for normal process exit, and signalled termination
information p_xsig.  Kernel-visible macro KW_EXITCODE() reconstructs
old p_xstat from p_xexit and p_xsig.  p_xexit contains complete status
and copied out into si_status.

Requested by:	Joerg Schilling
Reviewed by:	jilles (previous version), pho
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
2015-07-18 09:02:50 +00:00
Ed Schouten
6256e57ba9 Implement CloudABI memory management system calls.
Add support for the <sys/mman.h> functions by wrapping around our own
implementations. There are no kern_*() variants of these system calls,
but we also don't need them in this case. It is sufficient to just call
into the sys_*() functions.

Differential Revision:	https://reviews.freebsd.org/D3033
Reviewed by:		brooks
2015-07-17 09:00:38 +00:00
Ed Schouten
6e5fcd99df Add a sysentvec for CloudABI on x86-64.
Summary:
For CloudABI we need to put two things on the stack of new processes:
the argument data (a binary blob; not strings) and a startup data
structure. The startup data structure contains interesting things such
as a pointer to the ELF program header, the thread ID of the initial
thread, a stack smashing protection canary, and a pointer to the
argument data.

Fetching system call arguments and setting the return value is similar
to FreeBSD. The only differences are that system call 0 does not exist
and that we call into cloudabi_convert_errno() to convert the error
code. We also need this function in a couple of other places, so we'd
better reuse it here.

Reviewers: dchagin, kib

Reviewed By: kib

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3098
2015-07-16 18:24:06 +00:00
Ed Schouten
457f7e23b1 Implement CloudABI's exec() call.
Summary:
In a runtime that is purely based on capability-based security, there is
a strong emphasis on how programs start their execution. We need to make
sure that we execute an new program with an exact set of file
descriptors, ensuring that credentials are not leaked into the process
accidentally.

Providing the right file descriptors is just half the problem. There
also needs to be a framework in place that gives meaning to these file
descriptors. How does a CloudABI mail server know which of the file
descriptors corresponds to the socket that receives incoming emails?
Furthermore, how will this mail server acquire its configuration
parameters, as it cannot open a configuration file from a global path on
disk?

CloudABI solves this problem by replacing traditional string command
line arguments by tree-like data structure consisting of scalars,
sequences and mappings (similar to YAML/JSON). In this structure, file
descriptors are treated as a first-class citizen. When calling exec(),
file descriptors are passed on to the new executable if and only if they
are referenced from this tree structure. See the cloudabi-run(1) man
page for more details and examples (sysutils/cloudabi-utils).

Fortunately, the kernel does not need to care about this tree structure
at all. The C library is responsible for serializing and deserializing,
but also for extracting the list of referenced file descriptors. The
system call only receives a copy of the serialized data and a layout of
what the new file descriptor table should look like:

    int proc_exec(int execfd, const void *data, size_t datalen, const int *fds,
              size_t fdslen);

This change introduces a set of fd*_remapped() functions:

- fdcopy_remapped() pulls a copy of a file descriptor table, remapping
  all of the file descriptors according to the provided mapping table.
- fdinstall_remapped() replaces the file descriptor table of the process
  by the copy created by fdcopy_remapped().
- fdescfree_remapped() frees the table in case we aborted before
  fdinstall_remapped().

We then add a function exec_copyin_data_fds() that builds on top these
functions. It copies in the data and constructs a new remapped file
descriptor. This is used by cloudabi_sys_proc_exec().

Test Plan:
cloudabi-run(1) is capable of spawning processes successfully, providing
it data and file descriptors. procstat -f seems to confirm all is good.
Regular FreeBSD processes also work properly.

Reviewers: kib, mjg

Reviewed By: mjg

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3079
2015-07-16 07:05:42 +00:00
Ed Schouten
952c6e1010 Implement the trivial socket system calls: shutdown() and listen(). 2015-07-15 11:27:34 +00:00
Ed Schouten
4fa92fb538 Make posix_fallocate() and posix_fadvise() work.
We can map these system calls directly to the FreeBSD counterparts. The
other filesystem related system calls will be sent out for review
separately, as they are a bit more complex to get right.
2015-07-15 09:14:06 +00:00
Ed Schouten
707d98fe2f Implement the CloudABI random_get() system call.
The random_get() system call works similar to getentropy()/getrandom()
on OpenBSD/Linux. It fills a buffer with random data.

This change introduces a new function, read_random_uio(), that is used
to implement read() on the random devices. We can call into this
function from within the CloudABI compatibility layer.

Approved by:	secteam
Reviewed by:	jmg, markm, wblock
Obtained from:	https://github.com/NuxiNL/freebsd
Differential Revision:	https://reviews.freebsd.org/D3053
2015-07-14 18:45:15 +00:00
Ed Schouten
460ac6370a Regenerate system call table for r285540. 2015-07-14 15:12:24 +00:00
Ed Schouten
1eb7c7cae3 Implement thread_tcb_set() and thread_yield().
The first system call is used to set the user TLS address. Right now
this system call is invoked by the C library for both the initial thread
and additional threads unconditionally, but in the future we'll only
call this if the architecture does not support this. On recent x86-64
CPUs we could use the WRFSBASE instruction.

This system call was erroneously placed in sys/compat/cloudabi64, even
though it does not depend on any pointer size dependent datastructure.
Move it to the right place.

Obtained from:	https://github.com/NuxiNL/freebsd
2015-07-14 15:11:50 +00:00
Ed Schouten
03744d7c8d Implement {,p}{read,write}{,v}().
Add a routine similar to copyinuio() and freebsd32_copyinuio() that
copies in CloudABI's struct iovecs. These are then translated into
FreeBSD format and placed in a 'struct uio', so we can call into the
kern_*() functions.

Obtained from:	https://github.com/NuxiNL/freebsd
2015-07-14 14:33:21 +00:00
Ed Schouten
f9675092b8 Let proc_raise() call into pksignal() directly.
Summary:
As discussed with kib@ in response to r285404, don't call into
kern_sigaction() within proc_raise() to reset the signal to the default
action before delivery. We'd better do that during image execution.

Change the code to simply use pksignal(), so we don't waste cycles on
functions like pfind() to look up the currently running process itself.

Test Plan:
This change has also been pushed into the cloudabi branch on GitHub. The
raise() tests still seem to pass.

Reviewers: kib

Reviewed By: kib

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3076
2015-07-14 12:16:14 +00:00
Ed Schouten
4f1905177a Implement normal and abnormal process termination.
CloudABI does not provide an explicit kill() system call, for the reason
that there is no access to the global process namespace. Instead, it
offers a raise() system call that can at least be used to terminate the
process abnormally.

CloudABI does not support installing signal handlers. CloudABI's raise()
system call should behave as if the default policy is set up. Call into
kern_sigaction(SIG_DFL) before calling sys_kill() to force this.

Obtained from:	https://github.com/NuxiNL/freebsd
2015-07-11 19:41:31 +00:00
Ed Schouten
a4001f4cb9 Use FDDUP_NORMAL instead of hardcoding value 0.
Proposed by:	mjg
2015-07-11 18:53:30 +00:00
Ed Schouten
329d1bca7f Add missing function parameter.
A function parameter got added in r285356, meaning that the call to
kern_dup() needs to be patched up.
2015-07-11 18:39:16 +00:00
Mateusz Guzik
b34be824a0 linprocfs: vref the vnode passed to vn_fullpath 2015-07-11 16:44:28 +00:00
Mateusz Guzik
8a08cec166 Create a dedicated function for ensuring that cdir and rdir are populated.
Previously several places were doing it on its own, partially
incorrectly (e.g. without the filedesc locked) or even actively harmful
by populating jdir or assigning rootvnode without vrefing it.

Reviewed by:	kib
2015-07-11 16:22:48 +00:00