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g_bio.9freebsd

Langue: en

Version: 307516 (debian - 07/07/09)

Section: 9 (Appels noyau Linux)


BSD mandoc

NAME

g_new_bio g_clone_bio g_destroy_bio g_print_bio - GEOM bio controlling functions

SYNOPSIS

In sys/bio.h In geom/geom.h Ft struct bio * Fn g_new_bio void Ft struct bio * Fn g_alloc_bio void Ft struct bio * Fn g_clone_bio struct bio *bp Ft struct bio * Fn g_duplicate_bio struct bio *bp Ft void Fn g_destroy_bio struct bio *bp Ft void Fn g_print_bio struct bio *bp

DESCRIPTION

A Vt struct bio is used by GEOM to describe I/O requests, its most important fields are described below:
bio_cmd
I/O request command. There are four I/O requests available in GEOM:
BIO_READ
A read request.
BIO_WRITE
A write request.
BIO_DELETE
Indicates that a certain range of data is no longer used and that it can be erased or freed as the underlying technology supports. Technologies like flash adaptation layers can arrange to erase the relevant blocks before they will become reassigned and cryptographic devices may want to fill random bits into the range to reduce the amount of data available for attack.
BIO_GETATTR
Inspect and manipulate out-of-band attributes on a particular provider or path. Attributes are named by ascii strings and are stored in the bio_attribute field.
BIO_FLUSH
Tells underlying providers to flush their write caches.
bio_flags
Available flags:
BIO_ERROR
Request failed (error value is stored in bio_error field).
BIO_DONE
Request finished.
bio_cflags
Private use by the consumer.
bio_pflags
Private use by the provider.
bio_offset
Offset into provider.
bio_data
Pointer to data buffer.
bio_error
Error value when BIO_ERROR is set.
bio_done
Pointer to function which will be called when the request is finished.
bio_driver1
Private use by the provider.
bio_driver2
Private use by the provider.
bio_caller1
Private use by the consumer.
bio_caller2
Private use by the consumer.
bio_attribute
Attribute string for BIO_GETATTR request.
bio_from
Consumer to use for request (attached to provider stored in bio_to field) (typically read-only for a class).
bio_to
Destination provider (typically read-only for a class).
bio_length
Request length in bytes.
bio_completed
Number of bytes completed, but they may not be completed from the front of the request.
bio_children
Number of Vt bio clones (typically read-only for a class).
bio_inbed
Number of finished Vt bio clones.
bio_parent
Pointer to parent Vt bio .

The Fn g_new_bio function allocates a new, empty Vt bio structure.

Fn g_alloc_bio - same as Fn g_new_bio , but always succeeds (allocates bio with the M_WAITOK malloc flag).

The Fn g_clone_bio function allocates a new Vt bio structure and copies the following fields from the Vt bio given as an argument to clone: bio_cmd bio_length bio_offset bio_data bio_attribute The field bio_parent in the clone points to the passed Vt bio and the field bio_children in the passed Vt bio is incremented.

This function should be used for every request which enters through the provider of a particular geom and needs to be scheduled down. Proper order is:

  1. Clone the received Vt struct bio .
  2. Modify the clone.
  3. Schedule the clone on its own consumer.

Fn g_duplicate_bio - same as Fn g_clone_bio , but always succeeds (allocates bio with the M_WAITOK malloc flag).

The Fn g_destroy_bio function deallocates and destroys the given Vt bio structure.

The Fn g_print_bio function prints information about the given Vt bio structure (for debugging purposes).

RETURN VALUES

The Fn g_new_bio and Fn g_clone_bio functions return a pointer to the allocated Vt bio , or NULL if an error occurred.

EXAMPLES

Implementation of ``NULL -transformation '' meaning that an I/O request is cloned and scheduled down without any modifications. Let us assume that field ex_consumer in structure Vt example_softc contains a consumer attached to the provider we want to operate on.
 void
 example_start(struct bio *bp)
 {
         struct example_softc *sc;
         struct bio *cbp;
 
         printf("Request received: ");
         g_print_bio(bp);
         printf("\n");
 
         sc = bp->bio_to->geom->softc;
         if (sc == NULL) {
                 g_io_deliver(bp, ENXIO);
                 return;
         }
 
         /* Let's clone our bio request. */
         cbp = g_clone_bio(bp);
         if (cbp == NULL) {
                 g_io_deliver(bp, ENOMEM);
                 return;
         }
         cbp->bio_done = g_std_done;     /* Standard 'done' function. */
 
         /* Ok, schedule it down. */
         /*
          * The consumer can be obtained from
          * LIST_FIRST(&bp->bio_to->geom->consumers) as well,
          * if there is only one in our geom.
          */
         g_io_request(cbp, sc->ex_consumer);
 }
 

SEE ALSO

geom(4), DECLARE_GEOM_CLASS9, g_access9, g_attach9, 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 pjd@FreeBSD.org .
La différence entre l'amour et l'argent, c 'est que si on partage son
argent, il diminue. Tandis que si on partage son amour, il augmente.
L'idéal étant d'arriver à partager son amour avec quelqu'un qui a du
pognon.
-+- Philippe Geluck, Le chat -+-