dksubr(9) - Manual pages

NAME

dk_softc, dk_init, dk_attach, dk_detach, dk_open, dk_close, dk_size, dk_dump, dk_ioctl, dk_strategy, dk_strategy_defer, dk_strategy_pending, dk_start, dk_done, dk_drain, dk_discard, dk_getdefaultlabel, dk_getdisklabel — disk driver subroutines

SYNOPSIS

#include <sys/bufq.h>
#include <sys/disk.h>
#include <dev/dkvar.h>

void
dk_init(struct dk_softc *, device_t, int dtype);

void
dk_attach(struct dk_softc *);

void
dk_detach(struct dk_softc *);

int
dk_open(struct dk_softc *, dev_t, int flags, int fmt, struct lwp *);

int
dk_close(struct dk_softc *, dev_t, int flags, int fmt, struct lwp *);

int
dk_discard(struct dk_softc *, dev_t, off_t pos, off_t len);

int
dk_size(struct dk_softc *, dev_t);

int
dk_dump(struct dk_softc *, dev_t, daddr_t blkno, void *vav, size_t size);

int
dk_ioctl(struct dk_softc *, dev_t, u_long cmd, void *data, int flag, struct lwp *);

void
dk_strategy(struct dk_softc *, struct buf *);

int
dk_strategy_defer(struct dk_softc *, struct buf *);

int
dk_strategy_pending(struct dk_softc *);

void
dk_start(struct dk_softc *, struct buf *);

void
dk_done(struct dk_softc *, struct buf *);

int
dk_drain(struct dk_softc *);

void
dk_getdefaultlabel(struct dk_softc *, struct disklabel *);

void
dk_getdisklabel(struct dk_softc *, dev_t);

DESCRIPTION

The disk driver subroutines provide common functionality for all disk drivers to reduce the amount of replicated code. For many disk drivers, their corresponding entry points can be made mostly stubs.

The subroutines encapsulate data structures found in a driver's softc into

struct dk_softc {
	device_t		sc_dev;
	struct disk		sc_dkdev;
	struct bufq_state	sc_bufq;
	krndsource_t		sc_rnd_source;
...
}

The dk_softc structure therefore replaces the device_t member of the driver's softc struct.

The following is a brief description of each function in the framework:

dk_init(): Initialize the dk_softc structure.
dk_attach(): Attach framework after driver has attached the disk(9) subsystem, created a bufq(9) and is ready to handle I/O.
dk_detach(): Undo dk_attach.
dk_open(): Handles open steps for the disk(9) framework, acquires the disklabel and validates open parameters. The driver may provide the d_firstopen callback to handle initialization steps.
dk_close(): Handles close steps for the disk(9) framework. The driver may provide the d_lastclose callback to handle finalization steps. dk_open and dk_close are serialized by the openlock mutex.
dk_discard(): Validates parameters, computes raw block numbers and passes these to the d_discard callback.
dk_size(): Returns dump size information from the disklabel(9) and opens and closes the driver when necessary.
dk_dump(): Validates parameters, computes raw block numbers and iterates over the d_dumpblocks callback in appropriate chunks determined by the d_iosize callback.
dk_ioctl(): Handles the ioctls DIOCKLABEL, DIOCWLABEL, DIOCGDEFLABEL, DIOCGSTRATEGY, and DIOCSSTRATEGY and passes other disk ioctls through the disk(9) framework. Returns ENOTTY when an ioctl isn't implemented. This routine is run as a fallback to handle commands that are not specific to the driver.
dk_strategy(): Validates parameters, computes raw block numbers, queues a buffer for I/O and triggers queue processing by calling dk_start.
dk_strategy_defer(): Alternative to dk_strategy that only queues the buffer. Drivers that implement a separate I/O thread can use dk_strategy_defer within their own strategy routine and signal the thread through a private interface.
dk_strategy_pending(): This function is called by an I/O thread to determine if work has been queued by dk_strategy_defer. The driver must then call dk_start to trigger queue processing.
dk_start(): If bp != NULL put it into the queue. Run the d_diskstart callback for every buffer until the queue is empty or the callback returns EAGAIN. In the latter case, the buffer is saved and issued on the next queue run. This also calls disk_busy accordingly to handle I/O metrics.
dk_done(): Called by the driver when an I/O operation completed. dk_done logs errors, calls disk_unbusy to handle I/O metrics and collects entropy for the cprng(9).
dk_drain(): Aborts all queued I/O. This function must be called instead of bufq_drain() to cooperate with dk_start.
dk_getdefaultlabel(): Compute a common default disklabel for all disk drivers. Some drivers provide device specific information or assign specific disk formats to partitions. Such drivers may implement the d_label callback that is called by dk_getdefaultlabel after initializing the label with common values.
dk_getdisklabel(): Read disklabel with machine dependent low-level function readdisklabel and do sanity checks.

DRIVER INTERFACE

The driver needs to provide a common set of entry points that are used by the disk driver subroutines and the disk(9) framework.

struct dkdriver {
        void    (*d_strategy)(struct buf *);
        void    (*d_minphys)(struct buf *);
        int     (*d_open)(dev_t, int, int, struct lwp *);
        int     (*d_close)(dev_t, int, int, struct lwp *);
        int     (*d_diskstart)(device_t, struct buf *);
        void    (*d_iosize)(device_t, int *);
        int     (*d_dumpblocks)(device_t, void *, daddr_t, int);
        int     (*d_lastclose)(device_t);
        int     (*d_discard)(device_t, off_t, off_t);
        int     (*d_firstopen)(device_t, dev_t, int, int);
        void    (*d_label)(device_t, struct disklabel *);
};

d_strategy(): The driver strategy routine queues a single buffer for I/O and starts queue processing as appropriate.
d_minphys(): The driver minphys routine limits the buffer b_bcount to the maximum size for an I/O transfer supported by the driver and hardware. It also calls minphys to apply the platform limit.
d_open(): The driver open routine.
d_close(): The driver close routine.
d_diskstart(): Issues a single I/O request, called by dk_start.
d_iosize(): Truncate I/O size to the driver limit. This is similar to minphys but operates on an integer value instead of a buffer.
d_dumpblocks(): Issue a single I/O requests, called by dk_dump.
d_lastclose(): Private cleanup after last user is finished. Often used to flush write caches.
d_discard(): Issue a single I/O request to invalidate a disk region.
d_firstopen(): Private initialization when first user opens the driver.

HISTORY

The NetBSD common disk driver subroutines appeared in NetBSD 2.0 as a base for the cryptographic disk driver and was extended to handle disk wedges in NetBSD 4.0. Most functionality provided by ld(4) was included and extended in NetBSD 8.0 to support other disk drivers. The callback interface used by the disk(9) framework has been merged as well.

BUGS

The framework includes a dk_lookup helper function, that is used by the cgd(4) driver to open a vnode for a block device. This looks too generic and should be put somewhere better (and be renamed).

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