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.Dd January 16, 2004 26.Dt G_ACCESS 9 27.Os 28.Sh NAME 29.Nm g_access 30.Nd "control access to GEOM consumers and their providers" 31.Sh SYNOPSIS 32.In geom/geom.h 33.Ft int 34.Fn g_access "struct g_consumer *cp" "int dcr" "int dcw" "int dce" 35.Sh DESCRIPTION 36The 37.Fn g_access 38function allows to open, close, and generally change access to the provider 39which is attached to the given consumer 40.Fa cp . 41The arguments 42.Fa dcr , 43.Fa dcw , 44and 45.Fa dce 46represent relative read, write, and exclusive access count changes. 47Read and write access counts are self explanatory, and 48exclusive access counts deny write access to other interested parties. 49A provider's access count is the sum of the access counts of all 50attached consumers. 51.Pp 52After attaching a consumer to a provider with 53.Xr g_attach 9 , 54the 55.Fn g_access 56function has to be called on the consumer before starting I/O requests. 57.Sh RESTRICTIONS/CONDITIONS 58The consumer has to be attached to a provider. 59.Pp 60The intended change must not result in a negative access count. 61.Pp 62No-operation is not permitted 63.Fa ( dcr 64= 65.Fa dcw 66= 67.Fa dce 68= 69.Li 0 ) . 70.Pp 71The provider's geom must have an access method defined (e.g., 72.Va gp->access ) . 73.Pp 74The topology lock has to be held. 75.Sh RETURN VALUES 76The 77.Fn g_access 78function returns 0 if successful; otherwise an error code is returned. 79Note that 80.Fn g_access 81cannot fail when the arguments 82.Fa dcr , 83.Fa dcw , 84and 85.Fa dce 86are less than or equal to 0. 87.Sh EXAMPLES 88Create a consumer, attach it to a given provider, gain read access and 89read first sector. 90.Bd -literal -offset indent 91void 92some_function(struct g_geom *mygeom, struct g_provider *pp) 93{ 94 struct g_consumer *cp; 95 void *ptr; 96 int error; 97 98 g_topology_assert(); 99 100 /* Create new consumer on 'mygeom' geom. */ 101 cp = g_new_consumer(mygeom); 102 /* Attach newly created consumer to given provider. */ 103 if (g_attach(cp, pp) != 0) { 104 g_destroy_consumer(cp); 105 return; 106 } 107 /* Open provider for reading through our consumer. */ 108 error = g_access(cp, 1, 0, 0); 109 if (error != 0) { 110 printf("Cannot access provider: %s\\n", error); 111 g_detach(cp); 112 g_destroy_consumer(cp); 113 return; 114 } 115 116 /* 117 * Don't hold topology lock while reading. 118 */ 119 g_topology_unlock(); 120 ptr = g_read_data(cp, 0, pp->sectorsize, &error); 121 if (ptr == NULL) 122 printf("Error while reading: %d\\n", error); 123 /* 124 * Do something useful with data. 125 */ 126 g_topology_lock(); 127 128 /* Disconnect from provider (release access count). */ 129 g_access(cp, -1, 0, 0); 130 /* Detach from provider. */ 131 g_detach(cp); 132 /* Destroy consumer. */ 133 g_destroy_consumer(cp); 134} 135.Ed 136.Sh ERRORS 137Possible errors: 138.Bl -tag -width Er 139.It Bq Er EPERM 140The function is trying to open a provider with an exclusive access count, but 141it is already open for writing. 142.It Bq Er EPERM 143The function is trying to open a provider for writing, but it is already 144exclusively open. 145.El 146.Pp 147Any other error that can be returned by the provider's access method. 148.Sh SEE ALSO 149.Xr geom 4 , 150.Xr DECLARE_GEOM_CLASS 9 , 151.Xr g_attach 9 , 152.Xr g_bio 9 , 153.Xr g_consumer 9 , 154.Xr g_data 9 , 155.Xr g_event 9 , 156.Xr g_geom 9 , 157.Xr g_provider 9 , 158.Xr g_provider_by_name 9 , 159.Xr g_wither_geom 9 160.Sh AUTHORS 161.An -nosplit 162This manual page was written by 163.An Pawel Jakub Dawidek Aq Mt pjd@FreeBSD.org . 164