1.\" 2.\" Copyright (c) 2004 Pawel Jakub Dawidek <pjd@FreeBSD.org> 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 15.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 18.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd January 16, 2004 28.Dt G_ACCESS 9 29.Os 30.Sh NAME 31.Nm g_access 32.Nd "control access to GEOM consumers and their providers" 33.Sh SYNOPSIS 34.In geom/geom.h 35.Ft int 36.Fn g_access "struct g_consumer *cp" "int dcr" "int dcw" "int dce" 37.Sh DESCRIPTION 38The 39.Fn g_access 40function allows to open, close, and generally change access to the provider 41which is attached to the given consumer 42.Fa cp . 43The arguments 44.Fa dcr , 45.Fa dcw , 46and 47.Fa dce 48represent relative read, write, and exclusive access count changes. 49Read and write access counts are self explanatory, and 50exclusive access counts deny write access to other interested parties. 51A provider's access count is the sum of the access counts of all 52attached consumers. 53.Pp 54After attaching a consumer to a provider with 55.Xr g_attach 9 , 56the 57.Fn g_access 58function has to be called on the consumer before starting I/O requests. 59.Sh RESTRICTIONS/CONDITIONS 60The consumer has to be attached to a provider. 61.Pp 62The intended change must not result in a negative access count. 63.Pp 64No-operation is not permitted 65.Fa ( dcr 66= 67.Fa dcw 68= 69.Fa dce 70= 71.Li 0 ) . 72.Pp 73The provider's geom must have an access method defined (e.g., 74.Va gp->access ) . 75.Pp 76The topology lock has to be held. 77.Sh RETURN VALUES 78The 79.Fn g_access 80function returns 0 if successful; otherwise an error code is returned. 81Note that 82.Fn g_access 83cannot fail when the arguments 84.Fa dcr , 85.Fa dcw , 86and 87.Fa dce 88are less than or equal to 0. 89.Sh EXAMPLES 90Create a consumer, attach it to a given provider, gain read access and 91read first sector. 92.Bd -literal -offset indent 93void 94some_function(struct g_geom *mygeom, struct g_provider *pp) 95{ 96 struct g_consumer *cp; 97 void *ptr; 98 int error; 99 100 g_topology_assert(); 101 102 /* Create new consumer on 'mygeom' geom. */ 103 cp = g_new_consumer(mygeom); 104 /* Attach newly created consumer to given provider. */ 105 if (g_attach(cp, pp) != 0) { 106 g_destroy_consumer(cp); 107 return; 108 } 109 /* Open provider for reading through our consumer. */ 110 error = g_access(cp, 1, 0, 0); 111 if (error != 0) { 112 printf("Cannot access provider: %s\\n", error); 113 g_detach(cp); 114 g_destroy_consumer(cp); 115 return; 116 } 117 118 /* 119 * Don't hold topology lock while reading. 120 */ 121 g_topology_unlock(); 122 ptr = g_read_data(cp, 0, pp->sectorsize, &error); 123 if (ptr == NULL) 124 printf("Error while reading: %d\\n", error); 125 /* 126 * Do something useful with data. 127 */ 128 g_topology_lock(); 129 130 /* Disconnect from provider (release access count). */ 131 g_access(cp, -1, 0, 0); 132 /* Detach from provider. */ 133 g_detach(cp); 134 /* Destroy consumer. */ 135 g_destroy_consumer(cp); 136} 137.Ed 138.Sh ERRORS 139Possible errors: 140.Bl -tag -width Er 141.It Bq Er EPERM 142The function is trying to open a provider with an exclusive access count, but 143it is already open for writing. 144.It Bq Er EPERM 145The function is trying to open a provider for writing, but it is already 146exclusively open. 147.El 148.Pp 149Any other error that can be returned by the provider's access method. 150.Sh SEE ALSO 151.Xr geom 4 , 152.Xr DECLARE_GEOM_CLASS 9 , 153.Xr g_attach 9 , 154.Xr g_bio 9 , 155.Xr g_consumer 9 , 156.Xr g_data 9 , 157.Xr g_event 9 , 158.Xr g_geom 9 , 159.Xr g_provider 9 , 160.Xr g_provider_by_name 9 , 161.Xr g_wither_geom 9 162.Sh AUTHORS 163.An -nosplit 164This manual page was written by 165.An Pawel Jakub Dawidek Aq Mt pjd@FreeBSD.org . 166