#include <db.h>int db_jump_set(void *func, int which);
The db_jump_set function enables applications to replace underlying Berkeley DB library functionality by replacing entries in a function call jump table. The which argument specifies the entry to be replaced by the argument func.
No type checking is done of the func argument, and specifying an invalid replacement routine is likely to cause unpredictable results.
The following values of which are supported:
int dirfree(char **namesp, int cnt);
The namesp and cnt arguments are the same values as were returned by the DB_FUNC_DIRLIST function.
The dirfree function returns the value of errno on failure
and 0 on success.
The dir argument is the name of the directory to be searched.
The function must return a pointer to an array of nul-terminated file
names in the memory location referenced by the argument namesp,
and a count of the number of elements in the array in the memory location
referenced by cntp.
The dirlist function returns the value of errno on failure
and 0 on success.
The path argument is the pathname of the file to be checked.
If the isdirp argument is non-NULL, it must be set to non-0 if
path is a directory, and 0 if path is not a directory.
The exists function returns the value of errno on failure
and 0 on success.
The path argument is the pathname of the file to be checked, and the
fd argument is an open file descriptor on the file.
If the mbytesp and bytesp arguments are non-NULL, the
ioinfo function must return in them the size of the file: the
number of megabytes in the file into the memory location referenced by the
mbytesp argument, and the number of bytes over and above that number
of megabytes into the memory location referenced by the bytesp
argument.
In addition, if the iosizep argument is non-NULL, the ioinfo
function must return the optimum granularity for I/O operations to the file
in the memory location referenced by it.
The ioinfo function returns the value of errno on failure
and 0 on success.
The path argument is the name of a file.
The fd argument is an open file descriptor on that file.
The is_region argument will be zero if the intention is to map
a file into shared memory.
In this case, the map function must map the first len
bytes of the file into memory and return a pointer to the mapped
location in the memory location referenced by the argument addr.
In this case, the is_anonymous argument will always be zero.
The is_rdonly argument will be non-zero if the file is considered
read-only by the caller.
The is_region argument will be non-zero if the memory is intended
to be used as a shared memory region for synchronization between Berkeley DB
threads/processes.
In this case, the returned memory may be of any kind (e.g., anonymous),
but must be able to support semaphores.
If the application has previously specified that regions are to be
instantiated in anonymous memory (see DB_REGION_ANON below),
or the region is being joined and is believed to have been allocated
in anonymous shared memory, the is_anonymous argument will be
non-zero.
Additionally, the path and fd arguments may be ignored
(although future map calls using the same path must
return the same memory), and the is_rdonly argument will always
be zero.
By default, on UNIX systems, the Berkeley DB library will use the IEEE Std 1003.1b-1993 (POSIX)
mmap(2) interface to both map regular files into shared memory
and create shared memory regions.
If the application specifies that shared memory regions be instantiated
in anonymous memory (see DB_REGION_ANON below), the
shmget(2) shared memory segment interface will be used, where
available, and the MAP_ANON or MAP_ANONYMOUS options to
mmap(2) when shmget(2) is not available.
When using shmget 2(), shared memory regions are named, and so
multiple processes may share them.
When using the mmap MAP_ANON or MAP_ANONYMOUS options, shared
memory regions are not named, and so may only be accessed by a
single process and its threads.
You do not need to do this if your application can guarantee that only one
process will be accessing Berkeley DB files.
The map function returns the value of errno on failure
and 0 on success.
The path argument is the path argument specified to the DB_FUNC_MAP
function when the region was mapped into memory.
The runlink function returns the value of errno on failure
and 0 on success.
The fd argument is an open file descriptor on the file.
The seek function must cause a subsequent read from or write to the
file to occur at a byte offset specified by the calculation:
If rewind is non-zero, the byte offset is treated as a backwards
seek, not a forwards one.
The whence argument specifies where in the file the byte offset is
relative to, as described by the IEEE Std 1003.1b-1993 (POSIX) lseek system call.
The seek function returns the value of errno on failure
and 0 on success.
The seconds and microseconds arguments specify the amount
of time to wait until the suspending thread of control should run again.
The seconds and microseconds arguments may not be normalized
when the sleep function is called, i.e., the microseconds
argument may be greater than 1000000.
The sleep function returns the value of errno on failure
and 0 on success.
The addr argument is the argument returned by the DB_FUNC_MAP function
when the file or region was mapped into memory, and the len argument
is the same as the len argument specified to the DB_FUNC_MAP function
when the file or region was mapped into memory.
The unmap function returns the value of errno on failure
and 0 on success.
The yield function must be able to cause the rescheduling all
participants in the current Berkeley DB environment, whether threaded or not.
It may be incorrect to supply a thread yield function if more
than a single process is operating in the Berkeley DB environment.
This is because many thread-yield functions will not allow other processes
to run, and the contested lock may be held by another process, not by
another thread.
If no yield function is specified, or if the yield
function returns an error, the function specified by the DB_FUNC_SLEEP
entry will be used instead or subsequently, i.e., if no yield
function is specified, or it is possible for the yield function
to fail, the sleep function must cause the processor
to reschedule any waiting threads of control for execution.
The yield function returns the value of errno on failure
and 0 on success.
int dirlist(const char *dir, char ***namesp, int *cntp);
int exists(const char *path, int *isdirp);
int ioinfo(const char *path, int fd,
u_int32_t *mbytesp, u_int32_t *bytesp, u_int32_t *iosizep);
int map(char *path, int fd, size_t len,
int is_region, int is_anonymous, int is_rdonly,
void **addr);
db_value_set(1, DB_REGION_NAME);
int runlink(char *path);
int seek(int fd, size_t pgsize, db_pgno_t pageno,
u_int32_t relative, int rewind, int whence);(pgsize * pageno) + relative
int sleep(u_long seconds, u_long microseconds);
int unmap(void *addr, size_t len);
int yield(void);
Applications should be careful to replace related functions as a group and at the same time. Replacing DB_FUNC_MALLOC without replacing DB_FUNC_REALLOC is likely to result in unpredictable results.
The db_jump_set function returns the value of errno on failure, and 0 on success.