NAME
g_new_bio, g_clone_bio, g_destroy_bio, g_print_bio - GEOM bio controlling
functions
SYNOPSIS
#include <sys/bio.h>
#include <geom/geom.h>
struct bio *
g_new_bio(void);
struct bio *
g_alloc_bio(void);
struct bio *
g_clone_bio(struct bio *bp);
struct bio *
g_duplicate_bio(struct bio *bp);
void
g_destroy_bio(struct bio *bp);
void
g_print_bio(struct bio *bp);
DESCRIPTION
A 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 bio clones (typically read-only for a class).
bio_inbed Number of finished bio clones.
bio_parent Pointer to parent bio.
The g_new_bio() function allocates a new, empty bio structure.
g_alloc_bio() - same as g_new_bio(), but always succeeds (allocates bio
with the M_WAITOK malloc flag).
The g_clone_bio() function allocates a new bio structure and copies the
following fields from the 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 bio and the field bio_children in the
passed 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 struct bio.
2. Modify the clone.
3. Schedule the clone on its own consumer.
g_duplicate_bio() - same as g_clone_bio(), but always succeeds (allocates
bio with the M_WAITOK malloc flag).
The g_destroy_bio() function deallocates and destroys the given bio
structure.
The g_print_bio() function prints information about the given bio
structure (for debugging purposes).
RETURN VALUES
The g_new_bio() and g_clone_bio() functions return a pointer to the
allocated 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 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_CLASS(9), g_access(9), g_attach(9), g_consumer(9),
g_data(9), g_event(9), g_geom(9), g_provider(9), g_provider_by_name(9),
g_wither_geom(9)
AUTHORS
This manual page was written by Pawel Jakub Dawidek 〈pjd@FreeBSD.org〉.