table of contents
LOCK(9) | Kernel Developer's Manual | LOCK(9) |
NAME¶
lockinit
,
lockdestroy
,
lockmgr
,
lockmgr_args
,
lockmgr_args_rw
,
lockmgr_disown
,
lockmgr_printinfo
,
lockmgr_recursed
,
lockmgr_rw
,
lockmgr_waiters
,
lockstatus
,
lockmgr_assert
—
lockmgr family of functions
SYNOPSIS¶
#include
<sys/types.h>
#include
<sys/lock.h>
#include
<sys/lockmgr.h>
void
lockinit
(struct
lock *lkp, int
prio, const char
*wmesg, int
timo, int
flags);
void
lockdestroy
(struct
lock *lkp);
int
lockmgr
(struct
lock *lkp, u_int
flags, struct
mtx *ilk);
int
lockmgr_args
(struct
lock *lkp, u_int
flags, struct
mtx *ilk, const
char *wmesg, int
prio, int
timo);
int
lockmgr_args_rw
(struct
lock *lkp, u_int
flags, struct
rwlock *ilk,
const char
*wmesg, int
prio, int
timo);
void
lockmgr_disown
(struct
lock *lkp);
void
lockmgr_printinfo
(const
struct lock *lkp);
int
lockmgr_recursed
(const
struct lock *lkp);
int
lockmgr_rw
(struct
lock *lkp, u_int
flags, struct
rwlock *ilk);
int
lockmgr_waiters
(const
struct lock *lkp);
int
lockstatus
(const
struct lock *lkp);
options INVARIANTS
options INVARIANT_SUPPORT
void
lockmgr_assert
(const
struct lock *lkp,
int what);
DESCRIPTION¶
Thelockinit
() function is used to initialize
a lock. It must be called before any operation can be performed on a lock. Its
arguments are:
- lkp
- A pointer to the lock to initialize.
- prio
- The priority passed to sleep(9).
- wmesg
- The lock message. This is used for both debugging output and sleep(9).
- timo
- The timeout value passed to sleep(9).
- flags
- The flags the lock is to be initialized with:
LK_ADAPTIVE
- Enable adaptive spinning for this lock if the kernel is compiled with the ADAPTIVE_LOCKMGRS option.
LK_CANRECURSE
- Allow recursive exclusive locks.
LK_NOPROFILE
- Disable lock profiling for this lock.
LK_NOSHARE
- Allow exclusive locks only.
LK_NOWITNESS
- Instruct witness(4) to ignore this lock.
LK_NODUP
- witness(4) should log messages about duplicate locks being acquired.
LK_QUIET
- Disable ktr(4) logging for this lock.
LK_TIMELOCK
- Use timo during a sleep; otherwise, 0 is used.
lockdestroy
() function is used to destroy
a lock, and while it is called in a number of places in the kernel, it
currently does nothing.
The lockmgr
() and
lockmgr_rw
() functions handle general
locking functionality within the kernel, including support for shared and
exclusive locks, and recursion. lockmgr
()
and lockmgr_rw
() are also able to upgrade
and downgrade locks.
Their arguments are:
- lkp
- A pointer to the lock to manipulate.
- flags
- Flags indicating what action is to be taken.
LK_SHARED
- Acquire a shared lock. If an exclusive lock is currently held,
EDEADLK
will be returned. LK_EXCLUSIVE
- Acquire an exclusive lock. If an exclusive lock is already held, and
LK_CANRECURSE
is not set, the system will panic(9). LK_DOWNGRADE
- Downgrade exclusive lock to a shared lock. Downgrading a shared lock is not permitted. If an exclusive lock has been recursed, the system will panic(9).
LK_UPGRADE
- Upgrade a shared lock to an exclusive lock. If this call fails, the
shared lock is lost, even if the
LK_NOWAIT
flag is specified. During the upgrade, the shared lock could be temporarily dropped. Attempts to upgrade an exclusive lock will cause a panic(9). LK_TRYUPGRADE
- Try to upgrade a shared lock to an exclusive lock. The failure to upgrade does not result in the dropping of the shared lock ownership.
LK_RELEASE
- Release the lock. Releasing a lock that is not held can cause a panic(9).
LK_DRAIN
- Wait for all activity on the lock to end, then mark it decommissioned.
This is used before freeing a lock that is part of a piece of memory
that is about to be freed. (As documented in
<sys/lockmgr.h>
.) LK_SLEEPFAIL
- Fail if operation has slept.
LK_NOWAIT
- Do not allow the call to sleep. This can be used to test the lock.
LK_NOWITNESS
- Skip the witness(4) checks for this instance.
LK_CANRECURSE
- Allow recursion on an exclusive lock. For every lock there must be a release.
LK_INTERLOCK
- Unlock the interlock (which should be locked already).
- ilk
- An interlock mutex for controlling group access to the lock. If
LK_INTERLOCK
is specified,lockmgr
() andlockmgr_rw
() assume ilk is currently owned and not recursed, and will return it unlocked. See mtx_assert(9).
lockmgr_args
() and
lockmgr_args_rw
() function work like
lockmgr
() and
lockmgr_rw
() but accepting a
wmesg, timo
and prio on a per-instance basis. The
specified values will override the default ones, but this can still be used
passing, respectively, LK_WMESG_DEFAULT
,
LK_PRIO_DEFAULT
and
LK_TIMO_DEFAULT
.
The lockmgr_disown
() function switches the
owner from the current thread to be
LK_KERNPROC
, if the lock is already held.
The lockmgr_printinfo
() function prints
debugging information about the lock. It is used primarily by
VOP_PRINT(9) functions.
The lockmgr_recursed
() function returns true
if the lock is recursed, 0 otherwise.
The lockmgr_waiters
() function returns true
if the lock has waiters, 0 otherwise.
The lockstatus
() function returns the status
of the lock in relation to the current thread.
When compiled with options INVARIANTS
and
options INVARIANT_SUPPORT
, the
lockmgr_assert
() function tests
lkp for the assertions specified in
what, and panics if they are not met. One of
the following assertions must be specified:
KA_LOCKED
- Assert that the current thread has either a shared or an exclusive lock on the lkp lock pointed to by the first argument.
KA_SLOCKED
- Assert that the current thread has a shared lock on the lkp lock pointed to by the first argument.
KA_XLOCKED
- Assert that the current thread has an exclusive lock on the lkp lock pointed to by the first argument.
KA_UNLOCKED
- Assert that the current thread has no lock on the lkp lock pointed to by the first argument.
KA_LOCKED
,
KA_SLOCKED
, or
KA_XLOCKED
assertion:
KA_RECURSED
- Assert that the current thread has a recursed lock on lkp.
KA_NOTRECURSED
- Assert that the current thread does not have a recursed lock on lkp.
RETURN VALUES¶
Thelockmgr
() and
lockmgr_rw
() functions return 0 on success
and non-zero on failure.
The lockstatus
() function returns:
LK_EXCLUSIVE
- An exclusive lock is held by the current thread.
LK_EXCLOTHER
- An exclusive lock is held by someone other than the current thread.
LK_SHARED
- A shared lock is held.
0
- The lock is not held by anyone.
ERRORS¶
lockmgr
() and
lockmgr_rw
() fail if:
- [
EBUSY
] LK_FORCEUPGRADE
was requested and another thread had already requested a lock upgrade.- [
EBUSY
] LK_NOWAIT
was set, and a sleep would have been required, orLK_TRYUPGRADE
operation was not able to upgrade the lock.- [
ENOLCK
] LK_SLEEPFAIL
was set andlockmgr
() orlockmgr_rw
() did sleep.- [
EINTR
] PCATCH
was set in the lock priority, and a signal was delivered during a sleep. Note theERESTART
error below.- [
ERESTART
] PCATCH
was set in the lock priority, a signal was delivered during a sleep, and the system call is to be restarted.- [
EWOULDBLOCK
] - a non-zero timeout was given, and the timeout expired.
LOCKS¶
IfLK_INTERLOCK
is passed in the
flags argument to
lockmgr
() or
lockmgr_rw
(), the
ilk must be held prior to calling
lockmgr
() or
lockmgr_rw
(), and will be returned
unlocked.
Upgrade attempts that fail result in the loss of the lock that is currently
held. Also, it is invalid to upgrade an exclusive lock, and a
panic(9) will be the result of trying.
SEE ALSO¶
condvar(9), locking(9), mutex(9), rwlock(9), sleep(9), sx(9), mtx_assert(9), panic(9), VOP_PRINT(9)AUTHORS¶
This manual page was written by Chad David ⟨davidc@acns.ab.ca⟩.October 6, 2013 | Debian |