mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-22 11:17:19 +00:00
e551d45211
than defaulting the cmode argument to vn_open() to 0. Supply a default argument of ALQ_DEFAULT_CMODE (0600) in current callers. Discussed with/pointed out by: hmp Reveiwed by: jeff, hmp MFC after: 3 days
257 lines
6.1 KiB
Groff
257 lines
6.1 KiB
Groff
.\"
|
|
.\" Copyright (c) 2003 Hiten Pandya <hmp@FreeBSD.org>
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions, and the following disclaimer,
|
|
.\" without modification, immediately at the beginning of the file.
|
|
.\" 2. The name of the author may not be used to endorse or promote products
|
|
.\" derived from this software without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
|
|
.\" ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd May 16, 2003
|
|
.Dt ALQ 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm alq ,
|
|
.Nm alq_open ,
|
|
.Nm alq_write ,
|
|
.Nm alq_flush ,
|
|
.Nm alq_close ,
|
|
.Nm alq_get ,
|
|
.Nm alq_post
|
|
.Nd Asynchronous Logging Queues
|
|
.Sh SYNOPSIS
|
|
.In sys/alq.h
|
|
.Ft int
|
|
.Fo alq_open
|
|
.Fa "struct alq **app"
|
|
.Fa "const char *file"
|
|
.Fa "struct ucred *cred"
|
|
.Fa "int cmode"
|
|
.Fa "int size"
|
|
.Fa "int count"
|
|
.Fc
|
|
.Ft int
|
|
.Fn alq_write "struct alq *alq" "void *data" "int waitok"
|
|
.Ft void
|
|
.Fn alq_flush "struct alq *alq"
|
|
.Ft void
|
|
.Fn alq_close "struct alq *alq"
|
|
.Ft struct ale *
|
|
.Fn alq_get "struct alq *alq" "int waitok"
|
|
.Ft void
|
|
.Fn alq_post "struct alq *alq" "struct ale *ale"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm
|
|
facility provides an asynchronous fixed length recording
|
|
mechanism, known as Asynchronous Logging Queues.
|
|
It can record to any
|
|
.Xr vnode 9 ,
|
|
thus providing the ability to journal logs to character
|
|
devices as well as regular files.
|
|
All functions accept a
|
|
.Vt "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.
|
|
.Pp
|
|
An
|
|
.Dq asynchronous log entry
|
|
is defined as
|
|
.Vt "struct ale" ,
|
|
which has the following members:
|
|
.Bd -literal -offset indent
|
|
struct ale {
|
|
struct ale *ae_next; /* Next Entry */
|
|
char *ae_data; /* Entry buffer */
|
|
int ae_flags; /* Entry flags */
|
|
};
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Va ae_flags
|
|
field is for internal use, clients of the
|
|
.Nm
|
|
interface should not modify this field.
|
|
Behaviour is undefined if this field is modified.
|
|
.Sh FUNCTIONS
|
|
The
|
|
.Fn alq_open
|
|
function creates a new logging queue.
|
|
The
|
|
.Fa file
|
|
argument is the name of the file to open for logging; if the file does not
|
|
yet exist,
|
|
.Fn alq_open
|
|
will attempt to create it.
|
|
The
|
|
.Fa cmode
|
|
argument will be passed to
|
|
.Fn vn_open
|
|
as the requested creation mode, to be used if the file will be created by
|
|
.Fn alq_open .
|
|
Consumers of this API may wish to pass
|
|
.Dv ALQ_DEFAULT_CMODE ,
|
|
a default creation mode suitable for most applications.
|
|
The argument
|
|
.Fa cred
|
|
specifies the credentials to use when opening and performing I/O on the file.
|
|
The size of each entry in the queue is determined by
|
|
.Fa size .
|
|
The
|
|
.Fa count
|
|
argument determines the number of items to be stored in the
|
|
asynchronous queue over an approximate period of a disk
|
|
write operation.
|
|
.Pp
|
|
The
|
|
.Fn alq_write
|
|
function writes
|
|
.Fa data
|
|
to the designated queue,
|
|
.Fa alq .
|
|
In the event that
|
|
.Fn alq_write
|
|
could not write the entry immediately, and
|
|
.Dv ALQ_WAITOK
|
|
is passed to
|
|
.Fa waitok ,
|
|
then
|
|
.Fn alq_write
|
|
will be allowed to
|
|
.Xr tsleep 9 .
|
|
.Pp
|
|
The
|
|
.Fn alq_flush
|
|
function is used for flushing
|
|
.Fa alq
|
|
to the log medium that was passed to
|
|
.Fn alq_open .
|
|
.Pp
|
|
The
|
|
.Fn alq_close
|
|
function will close the asynchronous logging queue,
|
|
.Fa alq ,
|
|
and flush all pending write requests to the log medium.
|
|
It will free all resources that were previously allocated.
|
|
.Pp
|
|
The
|
|
.Fn alq_get
|
|
function returns the next available asynchronous logging entry
|
|
from the queue,
|
|
.Fa alq .
|
|
This function leaves the queue in a locked state, until a subsequent
|
|
.Fn alq_post
|
|
call is made.
|
|
In the event that
|
|
.Fn alq_get
|
|
could not retrieve an entry immediately, it will
|
|
.Xr tsleep 9
|
|
with the
|
|
.Dq Li alqget
|
|
wait message.
|
|
.Pp
|
|
The
|
|
.Fn alq_post
|
|
function schedules the asynchronous logging entry,
|
|
.Fa ale ,
|
|
which is retrieved using the
|
|
.Fn alq_get
|
|
function,
|
|
for writing to the asynchronous logging queue,
|
|
.Fa alq .
|
|
This function leaves the queue,
|
|
.Fa alq ,
|
|
in an unlocked state.
|
|
.Sh IMPLEMENTATION NOTES
|
|
The
|
|
.Fn alq_write
|
|
function is a wrapper around the
|
|
.Fn alq_get
|
|
and
|
|
.Fn alq_post
|
|
functions; by using these functions separately, a call
|
|
to
|
|
.Fn bcopy
|
|
can be avoided for performance critical code paths.
|
|
.Sh LOCKING
|
|
Each asynchronous queue is protected by a spin mutex.
|
|
.Pp
|
|
Functions
|
|
.Fn alq_flush ,
|
|
.Fn alq_open
|
|
and
|
|
.Fn alq_post
|
|
may attempt to acquire an internal sleep mutex, and should
|
|
consequently not be used in contexts where sleeping is
|
|
not allowed.
|
|
.Sh RETURN VALUES
|
|
The
|
|
.Fn alq_open
|
|
function returns one of the error codes listed in
|
|
.Xr open 2 ,
|
|
if it fails to open
|
|
.Fa file ,
|
|
or else it returns 0.
|
|
.Pp
|
|
The
|
|
.Fn alq_write
|
|
function returns
|
|
.Er EWOULDBLOCK
|
|
if
|
|
.Dv ALQ_NOWAIT
|
|
was provided as a value to
|
|
.Fa waitok
|
|
and either the queue is full, or when the system is shutting down.
|
|
.Pp
|
|
The
|
|
.Fn alq_get
|
|
function returns
|
|
.Dv NULL ,
|
|
if
|
|
.Dv ALQ_NOWAIT
|
|
was provided as a value to
|
|
.Fa waitok
|
|
and either the queue is full, or when the system is shutting down.
|
|
.Pp
|
|
NOTE: invalid arguments to non-void functions will result in
|
|
undefined behaviour.
|
|
.Sh SEE ALSO
|
|
.Xr syslog 3 ,
|
|
.Xr kthread 9 ,
|
|
.Xr ktr 9 ,
|
|
.Xr tsleep 9 ,
|
|
.Xr vnode 9
|
|
.Sh HISTORY
|
|
The
|
|
Asynchronous Logging Queues (ALQ) facility first appeared in
|
|
.Fx 5.0 .
|
|
.Sh AUTHORS
|
|
.An -nosplit
|
|
The
|
|
.Nm
|
|
facility was written by
|
|
.An Jeffrey Roberson Aq jeff@FreeBSD.org .
|
|
.Pp
|
|
This manual page was written by
|
|
.An Hiten Pandya Aq hmp@FreeBSD.org .
|