The OpenNET Project / Index page

[ новости /+++ | форум | теги | ]

Интерактивная система просмотра системных руководств (man-ов)

 ТемаНаборКатегория 
 
 [Cписок руководств | Печать]

g_access (9)
  • >> g_access (9) ( FreeBSD man: Ядро )

  • BSD mandoc
     

    NAME

    
    
    g_access
    
     - control access to GEOM consumers and their providers
    
     
    

    SYNOPSIS

       #include <geom/geom.h>
    int g_access (struct g_consumer *cp int dcr int dcw int dce);
     

    DESCRIPTION

    The 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.

    After attaching a consumer to a provider with g_attach9, the g_access ();
    function has to be called on the consumer before starting I/O requests.  

    RESTRICTIONS/CONDITIONS

    The consumer has to be attached to a provider.

    The intended change must not result in a negative access count.

    No-operation is not permitted Fa ( dcr = Fa dcw = Fa dce = 0 )

    The provider's geom must have an access method defined (e.g., gp->access )

    The topology lock has to be held.  

    RETURN VALUES

    The g_access ();
    function returns 0 if successful; otherwise an error code is returned. Note that g_access ();
    cannot fail when the arguments Fa dcr , Fa dcw , and Fa dce are less than or equal to 0.  

    EXAMPLES

    Create a consumer, attach it to a given provider, gain read access and read first sector.
    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);
    }
    
     

    ERRORS

    Possible errors:

    Bq Er EPERM
    The function is trying to open a provider with an exclusive access count, but it is already open for writing.
    Bq Er EPERM
    The function is trying to open a provider for writing, but it is already exclusively open.

    Any other error that can be returned by the provider's access method.  

    SEE ALSO

    geom(4), DECLARE_GEOM_CLASS9, g_attach9, g_bio9, g_consumer9, g_data9, g_event9, g_geom9, g_provider9, g_provider_by_name9, g_wither_geom9  

    AUTHORS

    An -nosplit This manual page was written by An Pawel Jakub Dawidek Aq [email protected] .


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    RESTRICTIONS/CONDITIONS
    RETURN VALUES
    EXAMPLES
    ERRORS
    SEE ALSO
    AUTHORS


    Поиск по тексту MAN-ов: 




    Партнёры:
    PostgresPro
    Inferno Solutions
    Hosting by Hoster.ru
    Хостинг:

    Закладки на сайте
    Проследить за страницей
    Created 1996-2024 by Maxim Chirkov
    Добавить, Поддержать, Вебмастеру