Copyright (c) 2004 Pawel Jakub Dawidek <pjd@FreeBSD.org>
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$FreeBSD: head/share/man/man9/g_access.9 127371 2004-03-24 14:25:46Z pjd $
.Dd January 16, 2004 .Dt g_access 9 .Os .Sh NAME .Nm g_access .Nd "control access count between given consumer and its provider" .Sh SYNOPSIS n 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/change access to/close the provider which is attached to the given consumer .Fa cp . Arguments .Fa dcr , .Fa dcw , .Fa dce stand for read, write and exclusive access count change. Read and write access are self explanatory. Exclusive access count prevents others write access. Provider's access count is the sum of all attached consumers counts. After attaching to the provider with .Fn g_attach function, one have to use .Fn g_access function before starting I/O requests. .Sh RESTRICTIONS/CONDITIONS The consumer must be attached.
p Change cannot result in negative access count.
p No-operation is not permitted .Fa ( dcr = .Fa dcw = .Fa dce = .Va 0 ) .
p Access method for provider's geom have to be defined (eg. gp->access).
p The topology lock must be held. .Sh RETURN VALUES .Fn g_attach returns the value 0 if successful; otherwise an error code is returned. .Sh ERRORS Possible errors: l -tag -width Er t Bq Er EPERM The function is trying to open with exclusive access count, but provider is already open for writting. t Bq Er EPERM The function is trying to open for write, but provider is already exclusively open. .El
p Any other error, than can be returned by provider's access method. .Sh EXAMPLES Create consumer, attach it to given provider, gain read access and read first sector. d -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 toplogy 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 SEE ALSO .Xr DECLARE_GEOM_CLASS 9 , .Xr geom 4 , .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 pjd@FreeBSD.org .