KERNHIST(9) | Kernel Developer's Manual | KERNHIST(9) |
kernhist
—
options KERNHIST
#include <sys/kernhist.h>
Below are the functions and macros provided by kernhist.h:
KERNHIST_DECL
(name);
KERNHIST_DEFINE
(name);
KERNHIST_INIT
(name,
unsigned
num_entries);
KERNHIST_INITIALIZER
(name,
void *buffer);
KERNHIST_INIT_STATIC
(struct
kern_history name, void
*buffer);
KERNHIST_LOG
(struct
kern_history name, const
char *fmt, u_long
arg0, u_long arg1,
u_long arg2,
u_long arg3);
KERNHIST_CALLARGS
(struct
kern_history name, const
char *fmt, u_long
arg0, u_long arg1,
u_long arg2,
u_long arg3);
KERNHIST_CALLED
(struct
kern_history name);
KERNHIST_FUNC
(fname);
KERNHIST_DUMP
(struct
kern_history name);
void
kernhist_dump
(struct
kern_history *history);
void
kernhist_dumpmask
(u_int32_t
bitmask);
void
kernhist_print
(void
(*pr)(const char *, ...));
kernhist
facility provides a very low-level tracing
facility that can be called extremely early in the kernel initialisation. It
provides a simple restricted
printf(3) format syntax with a
maximum of 4 arguments, each of type uintmax_t.
options KERNHIST
must be present in the
kernel configuration to enable these functions and macros.
A kernel history is a fixed-size buffer, either statically or dynamically allocated, that is written and read on a circular basis. Each entry includes the time the entry was made, the CPU from which the entry was recorded, the printf(3) like format string and length, the function name and length, the unique call count for this function, and the 4 arguments.
The history event data can be viewed using the
-U
and -u
histname options to
vmstat(1), or by using the
show kernhist
command in
ddb(4). User-written programs can
retrieve history data from the kernel using the
sysctl(9) variable
kern.hist.histname.
The format string must be a literal string that can be referenced later as it is not stored with the event (only a pointer to the format string is stored). It should only contain conversion specifiers suitable for uintmax_t sized values, such as “%jx”, “%ju”, and “%jo”, and address (pointer) arguments should be cast to uintptr_t to avoid compiler errors on architectures where pointers are smaller than uintmax_t integers. Conversion specifiers without a length modifier, and specifiers with length modifiers other than j, should not be used.
Conversion specifiers that require additional dereferences of their corresponding arguments, such as “%s”, will not work in vmstat(1), but will work when called from ddb(4).
These macros provide access to most kernel history functionality:
KERNHIST_DECL
(name)KERNHIST_DEFINE
(name)KERNHIST_INIT
(name,
num_entries)KERNHIST_INITIALIZER
(name,
buffer)KERNHIST_INIT_STATIC
(name,
buffer)KERNHIST_FUNC
(fname)kernhist
to be
used this function. Callable only once per function.KERNHIST_LOG
(name,
fmt, arg0,
arg1, arg2,
arg3)KERNHIST_CALLED
(name)KERNHIST_CALLARGS
() must be used once, near the
function entry point, to maintain the number of times the function has
been called.KERNHIST_CALLARGS
(name,
fmt, arg0,
arg1, arg2,
arg3)KERNHIST_CALLED
() and
KERNHIST_LOG
() that avoids having a
“called!” log message in addition to a message containing
normal arguments with a format string.KERNHIST_DUMP
(name)kernhist_dump
() on the named kernel
history.kernhist_dump
(history)kernhist_dumpmask
(bitmask)kernhist_print
(pr)pr
() argument is currently ignored.kernhist
functionality is implemented within the
files sys/sys/kernhist.h and
sys/kern/kern_history.c. The former file contains the
definitions of data structures used to export the data
via the sysctl(9) mechanism.
kernhist
facility first
appeared in NetBSD 1.4. The generalized version of
kernhist
appeared in NetBSD
6.0. The sysctl(9)
interface to kernhist
was introduced in
NetBSD 8.0.
kernhist
was originally written by
Charles D. Cranor as part of the
uvm(9) framework, under the name
UVMHIST. Matthew R. Green generalized it into its
current form to be available to non
uvm(9) frameworks.
Paul Goyette
<pgoyette@NetBSD.org>
provided the sysctl(9)
interface.
KERNHIST_FUNC
() could be converted to use
__func__ always, as all the callers already do.
The kernhist_dumpmask
() list of masks
could be properly published and made available, and as such this function
may be removed in a future release.
In addition to a statically-defined set of kernel histories, it would be possible to allow modular code to register and unregister their own histories dynamically, when a module is loaded or unloaded.
The kernhist_print
() function currently
ignores its pr argument.
October 25, 2017 | NetBSD 9.2 |