alq, alq_open, alq_write, alq_flush, alq_close, alq_get, alq_post --
Asynchronous Logging Queues
#include <sys/alq.h>
int
alq_open(struct alq **app, const char *file, int size, int count);
int
alq_write(struct alq *alq, void *data, int waitok);
void
alq_flush(struct alq *alq);
void
alq_close(struct alq *alq);
struct ale *
alq_get(struct alq *alq, int waitok);
void
alq_post(struct alq *alq, struct ale *ale);
The alq facility provides an asynchronous fixed length recording mechanism,
known as Asynchronous Logging Queues. It can record to any
vnode(9), thus providing the ability to journal logs to character devices
as well as regular files. All functions accept a struct alq argument,
which is an opaque type that maintains state information for an Asynchronous
Logging Queue. The logging facility runs in a separate kernel
thread, which services all log entry requests.
An ``asynchronous log entry'', is defined as struct ale, which has the
following members:
struct ale {
struct ale *ae_next; /* Next Entry */
char *ae_data; /* Entry buffer */
int ae_flags; /* Entry flags */
};
The ae_flags field is for internal use, clients of the alq interface
should not modify this field. Behaviour is undefined if this field is
modified.
The alq_open() function creates a new logging queue.
The file argument is the name of the file to open for logging, The size
of each entry in the queue is determined by size. The count argument
determines the number of items to be stored in the asynchronous queue
over an approximate period of a disk write operation.
The alq_write() function writes data to the designated queue, alq. In
the event that alq_write() could not write the entry immediately, and
ALQ_WAITOK is passed to waitok, then alq_write() will be allowed to
tsleep(9).
The alq_flush() function is used for flushing alq to the log medium that
was passed to alq_open().
The alq_close() function will close the asynchronous logging queue, alq,
and flush all pending write requests to the log medium. It will free all
resources that were previously allocated.
The alq_get() function returns the next available asynchronous logging
entry from the queue, alq. This function leaves the queue in a locked
state, until a subsequent alq_post() call is made. In the event that
alq_get() could not retrieve an entry immediately, it will tsleep(2) with
the ``alqget'' wait message.
The alq_post() function schedules the asynchronous logging entry, ale,
which is retrieved using the alq_get() function, for writing to the asynchronous
logging queue, alq. This function leaves the queue, alq, in an
unlocked state.
The alq_open() function uses the credentials of the invoking thread for
opening files. The alq_write() function is a wrapper around the
alq_get() and alq_post() functions; by using these functions separately,
a call to bcopy() can be avoided for performance critical code paths.
The alq_open() function returns one of the error codes listed in open(2),
if it fails to open file, or else it returns 0.
The alq_write() function returns EWOULDBLOCK if ALQ_NOWAIT was provided
as a value to waitok and either the queue is full, or when the system is
shutting down.
The alq_get() function returns NULL, if ALQ_NOWAIT was provided as a
value to waitok and either the queue is full, or when the system is shutting
down.
NOTE, invalid arguments to non-void functions will result in undefined
behaviour.
syslog(3), kthread(9), ktr(9), tsleep(9), vnode(9)
The Asynchronous Logging Queues (ALQ) facility first appeared in
FreeBSD 5.0
The alq facility was written by Jeffrey Roberson <[email protected]>.
This manual page was written by Hiten M. Pandya <[email protected]>.
FreeBSD 5.2.1 May 16, 2003 FreeBSD 5.2.1 [ Back ] |
