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32 .Nd "control access to GEOM consumers and their providers"
36 .Fn g_access "struct g_consumer *cp" "int dcr" "int dcw" "int dce"
40 function allows to open, close, and generally change access to the provider
41 which is attached to the given consumer
48 represent relative read, write, and exclusive access count changes.
49 Read and write access counts are self explanatory, and
50 exclusive access counts deny write access to other interested parties.
51 A provider's access count is the sum of the access counts of all
54 After attaching a consumer to a provider with
58 function has to be called on the consumer before starting I/O requests.
59 .Sh RESTRICTIONS/CONDITIONS
60 The consumer has to be attached to a provider.
62 The intended change must not result in a negative access count.
64 No-operation is not permitted
73 The provider's geom must have an access method defined (e.g.,
76 The topology lock has to be held.
80 function returns 0 if successful; otherwise an error code is returned.
83 cannot fail when the arguments
88 are less than or equal to 0.
93 The function is trying to open a provider with an exclusive access count, but
94 it is already open for writing.
96 The function is trying to open a provider for writing, but it is already
100 Any other error that can be returned by the provider's access method.
102 Create a consumer, attach it to a given provider, gain read access and
104 .Bd -literal -offset indent
106 some_function(struct g_geom *mygeom, struct g_provider *pp)
108 struct g_consumer *cp;
114 /* Create new consumer on 'mygeom' geom. */
115 cp = g_new_consumer(mygeom);
116 /* Attach newly created consumer to given provider. */
117 if (g_attach(cp, pp) != 0) {
118 g_destroy_consumer(cp);
121 /* Open provider for reading through our consumer. */
122 error = g_access(cp, 1, 0, 0);
124 printf("Cannot access provider: %s\\n", error);
126 g_destroy_consumer(cp);
131 * Don't hold topology lock while reading.
134 ptr = g_read_data(cp, 0, pp->sectorsize, &error);
136 printf("Error while reading: %d\\n", error);
138 * Do something useful with data.
142 /* Disconnect from provider (release access count). */
143 g_access(cp, -1, 0, 0);
144 /* Detach from provider. */
146 /* Destroy consumer. */
147 g_destroy_consumer(cp);
152 .Xr DECLARE_GEOM_CLASS 9 ,
160 .Xr g_provider_by_name 9 ,
164 This manual page was written by
165 .An Pawel Jakub Dawidek Aq pjd@FreeBSD.org .