307 lines
7.2 KiB
Groff
307 lines
7.2 KiB
Groff
.\"
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.\" Copyright (c) 2004-2006 Pawel Jakub Dawidek <pjd@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd Mar 7, 2018
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.Dt G_BIO 9
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.Os
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.Sh NAME
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.Nm g_new_bio ,
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.Nm g_clone_bio ,
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.Nm g_destroy_bio ,
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.Nm g_print_bio ,
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.Nm g_reset_bio
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.Nd "GEOM bio controlling functions"
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.Sh SYNOPSIS
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.In sys/bio.h
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.In geom/geom.h
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.Ft "struct bio *"
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.Fn g_new_bio void
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.Ft "struct bio *"
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.Fn g_alloc_bio void
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.Ft "struct bio *"
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.Fn g_clone_bio "struct bio *bp"
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.Ft "struct bio *"
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.Fn g_duplicate_bio "struct bio *bp"
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.Ft void
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.Fn g_destroy_bio "struct bio *bp"
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.Ft void
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.Fn g_print_bio "struct bio *bp"
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.Ft void
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.Fn g_reset_bio "struct bio *bp"
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.Sh DESCRIPTION
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A
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.Vt "struct bio"
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is used by GEOM to describe I/O requests, its
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most important fields are described below:
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.Bl -tag -width ".Va bio_attribute"
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.It Va bio_cmd
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I/O request command.
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There are five I/O requests available in GEOM:
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.Bl -tag -width ".Dv BIO_GETATTR"
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.It Dv BIO_READ
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A read request.
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.It Dv BIO_WRITE
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A write request.
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.It Dv BIO_DELETE
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Indicates that a certain range of data is no longer used and that
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it can be erased or freed as the underlying technology supports.
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Technologies like flash adaptation layers can arrange to erase the relevant
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blocks before they will become reassigned and cryptographic devices may
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want to fill random bits into the range to reduce the amount of data
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available for attack.
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.It Dv BIO_GETATTR
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Inspect and manipulate out-of-band
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attributes on a particular provider or path.
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Attributes are named by ascii strings and are stored in the
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.Va bio_attribute
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field.
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.It Dv BIO_FLUSH
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Tells underlying providers to flush their write caches.
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.El
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.It Va bio_flags
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Available flags:
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.Bl -tag -width ".Dv BIO_ERROR"
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.It Dv BIO_ERROR
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Request failed (error value is stored in
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.Va bio_error
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field).
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.It Dv BIO_DONE
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Request finished.
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.El
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.It Va bio_cflags
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Private use by the consumer.
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.It Va bio_pflags
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Private use by the provider.
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.It Va bio_offset
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Offset into provider.
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.It Va bio_data
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Pointer to data buffer.
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.It Va bio_error
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Error value when
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.Dv BIO_ERROR
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is set.
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.It Va bio_done
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Pointer to function which will be called when the request is finished.
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.It Va bio_driver1
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Private use by the provider.
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.It Va bio_driver2
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Private use by the provider.
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.It Va bio_caller1
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Private use by the consumer.
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.It Va bio_caller2
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Private use by the consumer.
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.It Va bio_attribute
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Attribute string for
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.Dv BIO_GETATTR
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request.
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.It Va bio_from
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Consumer to use for request (attached to provider stored in
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.Va bio_to
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field) (typically read-only for a class).
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.It Va bio_to
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Destination provider (typically read-only for a class).
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.It Va bio_length
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Request length in bytes.
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.It Va bio_completed
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Number of bytes completed, but they may not be completed from
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the front of the request.
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.It Va bio_children
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Number of
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.Vt bio
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clones (typically read-only for a class).
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.It Va bio_inbed
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Number of finished
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.Vt bio
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clones.
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.It Va bio_parent
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Pointer to parent
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.Vt bio .
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.El
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.Pp
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The
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.Fn g_new_bio
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function allocates a new, empty
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.Vt bio
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structure.
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.Pp
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.Fn g_alloc_bio
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- same as
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.Fn g_new_bio ,
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but always succeeds (allocates bio with the
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.Dv M_WAITOK
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malloc flag).
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.Pp
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The
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.Fn g_clone_bio
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function allocates a new
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.Vt bio
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structure and copies the following fields from the
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.Vt bio
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given as an argument to clone:
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.Va bio_cmd ,
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.Va bio_length ,
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.Va bio_offset ,
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.Va bio_data ,
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.Va bio_attribute .
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The field
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.Va bio_parent
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in the clone points to the passed
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.Vt bio
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and the field
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.Va bio_children
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in the passed
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.Vt bio
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is incremented.
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.Pp
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This function should be used for every request which enters through
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the provider of a particular geom and needs to be scheduled down.
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Proper order is:
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.Pp
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.Bl -enum -compact
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.It
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Clone the received
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.Vt "struct bio" .
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.It
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Modify the clone.
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.It
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Schedule the clone on its own consumer.
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.El
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.Pp
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.Fn g_duplicate_bio
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- same as
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.Fn g_clone_bio ,
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but always succeeds (allocates bio with the
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.Dv M_WAITOK
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malloc flag).
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.Pp
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The
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.Fn g_destroy_bio
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function deallocates and destroys the given
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.Vt bio
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structure.
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.Pp
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The
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.Fn g_print_bio
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function prints information about the given
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.Vt bio
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structure (for debugging purposes).
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.Pp
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The
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.Fn g_reset_bio
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function resets the given
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.Vt bio
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structure back to its initial state.
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.Fn g_reset_bio
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preserves internal data structures, while setting all
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user visible fields to their initial values.
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When reusing a
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.Vt bio
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obtained from
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.Fn g_new_bio ,
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.Fn g_alloc_bio ,
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.Fn g_clone_bio ,
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or
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.Fn g_duplicate_bio
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for multiple transactions,
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.Fn g_reset_bio
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must be called between the transactions in lieu of
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.Fn bzero .
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While not strictly required for a
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.Vt bio
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structure created by other means,
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.Fn g_reset_bio
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should be used to initialize it and between transactions.
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.Sh RETURN VALUES
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The
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.Fn g_new_bio
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and
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.Fn g_clone_bio
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functions return a pointer to the allocated
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.Vt bio ,
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or
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.Dv NULL
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if an error occurred.
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.Sh EXAMPLES
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Implementation of
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.Dq Dv NULL Ns -transformation ,
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meaning that an I/O request is cloned and scheduled down without any
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modifications.
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Let us assume that field
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.Va ex_consumer
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in structure
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.Vt example_softc
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contains a consumer attached to the provider we want to operate on.
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.Bd -literal -offset indent
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void
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example_start(struct bio *bp)
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{
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struct example_softc *sc;
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struct bio *cbp;
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printf("Request received: ");
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g_print_bio(bp);
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printf("\\n");
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sc = bp->bio_to->geom->softc;
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if (sc == NULL) {
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g_io_deliver(bp, ENXIO);
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return;
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}
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/* Let's clone our bio request. */
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cbp = g_clone_bio(bp);
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if (cbp == NULL) {
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g_io_deliver(bp, ENOMEM);
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return;
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}
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cbp->bio_done = g_std_done; /* Standard 'done' function. */
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/* Ok, schedule it down. */
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/*
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* The consumer can be obtained from
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* LIST_FIRST(&bp->bio_to->geom->consumer) as well,
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* if there is only one in our geom.
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*/
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g_io_request(cbp, sc->ex_consumer);
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}
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.Ed
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.Sh SEE ALSO
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.Xr geom 4 ,
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.Xr DECLARE_GEOM_CLASS 9 ,
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.Xr g_access 9 ,
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.Xr g_attach 9 ,
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.Xr g_consumer 9 ,
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.Xr g_data 9 ,
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.Xr g_event 9 ,
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.Xr g_geom 9 ,
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.Xr g_provider 9 ,
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.Xr g_provider_by_name 9 ,
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.Xr g_wither_geom 9
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.Sh AUTHORS
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.An -nosplit
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This manual page was written by
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.An Pawel Jakub Dawidek Aq Mt pjd@FreeBSD.org .
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