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diff --git a/share/man/man9/g_access.9 b/share/man/man9/g_access.9 new file mode 100644 index 0000000..fcfc869 --- /dev/null +++ b/share/man/man9/g_access.9 @@ -0,0 +1,165 @@ +.\" +.\" Copyright (c) 2004 Pawel Jakub Dawidek <pjd@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. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``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 DEVELOPERS 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 January 16, 2004 +.Dt G_ACCESS 9 +.Os +.Sh NAME +.Nm g_access +.Nd "control access to GEOM consumers and their providers" +.Sh SYNOPSIS +.In geom/geom.h +.Ft int +.Fn g_access "struct g_consumer *cp" "int dcr" "int dcw" "int dce" +.Sh DESCRIPTION +The +.Fn g_access +function allows to open, close, and generally change access to the provider +which is attached to the given consumer +.Fa cp . +The arguments +.Fa dcr , +.Fa dcw , +and +.Fa dce +represent relative read, write, and exclusive access count changes. +Read and write access counts are self explanatory, and +exclusive access counts deny write access to other interested parties. +A provider's access count is the sum of the access counts of all +attached consumers. +.Pp +After attaching a consumer to a provider with +.Xr g_attach 9 , +the +.Fn g_access +function has to be called on the consumer before starting I/O requests. +.Sh RESTRICTIONS/CONDITIONS +The consumer has to be attached to a provider. +.Pp +The intended change must not result in a negative access count. +.Pp +No-operation is not permitted +.Fa ( dcr += +.Fa dcw += +.Fa dce += +.Li 0 ) . +.Pp +The provider's geom must have an access method defined (e.g., +.Va gp->access ) . +.Pp +The topology lock has to be held. +.Sh RETURN VALUES +The +.Fn g_access +function returns 0 if successful; otherwise an error code is returned. +Note that +.Fn g_access +cannot fail when the arguments +.Fa dcr , +.Fa dcw , +and +.Fa dce +are less than or equal to 0. +.Sh EXAMPLES +Create a consumer, attach it to a given provider, gain read access and +read first sector. +.Bd -literal -offset indent +void +some_function(struct g_geom *mygeom, struct g_provider *pp) +{ + struct g_consumer *cp; + void *ptr; + int error; + + g_topology_assert(); + + /* Create new consumer on 'mygeom' geom. */ + cp = g_new_consumer(mygeom); + /* Attach newly created consumer to given provider. */ + if (g_attach(cp, pp) != 0) { + g_destroy_consumer(cp); + return; + } + /* Open provider for reading through our consumer. */ + error = g_access(cp, 1, 0, 0); + if (error != 0) { + printf("Cannot access provider: %s\\n", error); + g_detach(cp); + g_destroy_consumer(cp); + return; + } + + /* + * Don't hold topology lock while reading. + */ + g_topology_unlock(); + ptr = g_read_data(cp, 0, pp->sectorsize, &error); + if (ptr == NULL) + printf("Error while reading: %d\\n", error); + /* + * Do something useful with data. + */ + g_topology_lock(); + + /* Disconnect from provider (release access count). */ + g_access(cp, -1, 0, 0); + /* Detach from provider. */ + g_detach(cp); + /* Destroy consumer. */ + g_destroy_consumer(cp); +} +.Ed +.Sh ERRORS +Possible errors: +.Bl -tag -width Er +.It Bq Er EPERM +The function is trying to open a provider with an exclusive access count, but +it is already open for writing. +.It Bq Er EPERM +The function is trying to open a provider for writing, but it is already +exclusively open. +.El +.Pp +Any other error that can be returned by the provider's access method. +.Sh SEE ALSO +.Xr geom 4 , +.Xr DECLARE_GEOM_CLASS 9 , +.Xr g_attach 9 , +.Xr g_bio 9 , +.Xr g_consumer 9 , +.Xr g_data 9 , +.Xr g_event 9 , +.Xr g_geom 9 , +.Xr g_provider 9 , +.Xr g_provider_by_name 9 , +.Xr g_wither_geom 9 +.Sh AUTHORS +.An -nosplit +This manual page was written by +.An Pawel Jakub Dawidek Aq Mt pjd@FreeBSD.org . |
