bsg: support for full generic block layer SG v3

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 997 insertions, 0 deletions

diff --git a/block/bsg.c b/block/bsg.c
new file mode 100644
index 00000000000..724b69391cd
--- /dev/null
+++ b/block/bsg.c
@@ -0,0 +1,997 @@
+/*
+ * bsg.c - block layer implementation of the sg v3 interface
+ *
+ * Copyright (C) 2004 Jens Axboe <axboe@suse.de> SUSE Labs
+ * Copyright (C) 2004 Peter M. Jones <pjones@redhat.com>
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License version 2.  See the file "COPYING" in the main directory of this
+ *  archive for more details.
+ *
+ */
+/*
+ * TODO
+ *      - Should this get merged, block/scsi_ioctl.c will be migrated into
+ *        this file. To keep maintenance down, it's easier to have them
+ *        seperated right now.
+ *
+ */
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/file.h>
+#include <linux/blkdev.h>
+#include <linux/poll.h>
+#include <linux/cdev.h>
+#include <linux/percpu.h>
+#include <linux/uio.h>
+#include <linux/bsg.h>
+
+#include <scsi/scsi.h>
+#include <scsi/scsi_ioctl.h>
+#include <scsi/scsi_cmnd.h>
+#include <scsi/sg.h>
+
+static char bsg_version[] = "block layer sg (bsg) 0.4";
+
+struct bsg_command;
+
+struct bsg_device {
+        struct gendisk *disk;
+        request_queue_t *queue;
+        spinlock_t lock;
+        struct list_head busy_list;
+        struct list_head done_list;
+        struct hlist_node dev_list;
+        atomic_t ref_count;
+        int minor;
+        int queued_cmds;
+        int done_cmds;
+        unsigned long *cmd_bitmap;
+        struct bsg_command *cmd_map;
+        wait_queue_head_t wq_done;
+        wait_queue_head_t wq_free;
+        char name[BDEVNAME_SIZE];
+        int max_queue;
+        unsigned long flags;
+};
+
+enum {
+        BSG_F_BLOCK             = 1,
+        BSG_F_WRITE_PERM        = 2,
+};
+
+/*
+ * command allocation bitmap defines
+ */
+#define BSG_CMDS_PAGE_ORDER     (1)
+#define BSG_CMDS_PER_LONG       (sizeof(unsigned long) * 8)
+#define BSG_CMDS_MASK           (BSG_CMDS_PER_LONG - 1)
+#define BSG_CMDS_BYTES          (PAGE_SIZE * (1 << BSG_CMDS_PAGE_ORDER))
+#define BSG_CMDS                (BSG_CMDS_BYTES / sizeof(struct bsg_command))
+
+#undef BSG_DEBUG
+
+#ifdef BSG_DEBUG
+#define dprintk(fmt, args...) printk(KERN_ERR "%s: " fmt, __FUNCTION__, ##args)
+#else
+#define dprintk(fmt, args...)
+#endif
+
+#define list_entry_bc(entry)    list_entry((entry), struct bsg_command, list)
+
+/*
+ * just for testing
+ */
+#define BSG_MAJOR       (240)
+
+static DEFINE_MUTEX(bsg_mutex);
+static int bsg_device_nr;
+
+#define BSG_LIST_SIZE   (8)
+#define bsg_list_idx(minor)     ((minor) & (BSG_LIST_SIZE - 1))
+static struct hlist_head bsg_device_list[BSG_LIST_SIZE];
+
+static struct class *bsg_class;
+static LIST_HEAD(bsg_class_list);
+
+/*
+ * our internal command type
+ */
+struct bsg_command {
+        struct bsg_device *bd;
+        struct list_head list;
+        struct request *rq;
+        struct bio *bio;
+        int err;
+        struct sg_io_hdr hdr;
+        struct sg_io_hdr __user *uhdr;
+        char sense[SCSI_SENSE_BUFFERSIZE];
+};
+
+static void bsg_free_command(struct bsg_command *bc)
+{
+        struct bsg_device *bd = bc->bd;
+        unsigned long bitnr = bc - bd->cmd_map;
+        unsigned long flags;
+
+        dprintk("%s: command bit offset %lu\n", bd->name, bitnr);
+
+        spin_lock_irqsave(&bd->lock, flags);
+        bd->queued_cmds--;
+        __clear_bit(bitnr, bd->cmd_bitmap);
+        spin_unlock_irqrestore(&bd->lock, flags);
+
+        wake_up(&bd->wq_free);
+}
+
+static struct bsg_command *__bsg_alloc_command(struct bsg_device *bd)
+{
+        struct bsg_command *bc = NULL;
+        unsigned long *map;
+        int free_nr;
+
+        spin_lock_irq(&bd->lock);
+
+        if (bd->queued_cmds >= bd->max_queue)
+                goto out;
+
+        for (free_nr = 0, map = bd->cmd_bitmap; *map == ~0UL; map++)
+                free_nr += BSG_CMDS_PER_LONG;
+
+        BUG_ON(*map == ~0UL);
+
+        bd->queued_cmds++;
+        free_nr += ffz(*map);
+        __set_bit(free_nr, bd->cmd_bitmap);
+        spin_unlock_irq(&bd->lock);
+
+        bc = bd->cmd_map + free_nr;
+        memset(bc, 0, sizeof(*bc));
+        bc->bd = bd;
+        INIT_LIST_HEAD(&bc->list);
+        dprintk("%s: returning free cmd %p (bit %d)\n", bd->name, bc, free_nr);
+        return bc;
+out:
+        dprintk("%s: failed (depth %d)\n", bd->name, bd->queued_cmds);
+        spin_unlock_irq(&bd->lock);
+        return bc;
+}
+
+static inline void
+bsg_del_done_cmd(struct bsg_device *bd, struct bsg_command *bc)
+{
+        bd->done_cmds--;
+        list_del(&bc->list);
+}
+
+static inline void
+bsg_add_done_cmd(struct bsg_device *bd, struct bsg_command *bc)
+{
+        bd->done_cmds++;
+        list_add_tail(&bc->list, &bd->done_list);
+        wake_up(&bd->wq_done);
+}
+
+static inline int bsg_io_schedule(struct bsg_device *bd, int state)
+{
+        DEFINE_WAIT(wait);
+        int ret = 0;
+
+        spin_lock_irq(&bd->lock);
+
+        BUG_ON(bd->done_cmds > bd->queued_cmds);
+
+        /*
+         * -ENOSPC or -ENODATA?  I'm going for -ENODATA, meaning "I have no
+         * work to do", even though we return -ENOSPC after this same test
+         * during bsg_write() -- there, it means our buffer can't have more
+         * bsg_commands added to it, thus has no space left.
+         */
+        if (bd->done_cmds == bd->queued_cmds) {
+                ret = -ENODATA;
+                goto unlock;
+        }
+
+        if (!test_bit(BSG_F_BLOCK, &bd->flags)) {
+                ret = -EAGAIN;
+                goto unlock;
+        }
+
+        prepare_to_wait(&bd->wq_done, &wait, state);
+        spin_unlock_irq(&bd->lock);
+        io_schedule();
+        finish_wait(&bd->wq_done, &wait);
+
+        if ((state == TASK_INTERRUPTIBLE) && signal_pending(current))
+                ret = -ERESTARTSYS;
+
+        return ret;
+unlock:
+        spin_unlock_irq(&bd->lock);
+        return ret;
+}
+
+/*
+ * get a new free command, blocking if needed and specified
+ */
+static struct bsg_command *bsg_get_command(struct bsg_device *bd)
+{
+        struct bsg_command *bc;
+        int ret;
+
+        do {
+                bc = __bsg_alloc_command(bd);
+                if (bc)
+                        break;
+
+                ret = bsg_io_schedule(bd, TASK_INTERRUPTIBLE);
+                if (ret) {
+                        bc = ERR_PTR(ret);
+                        break;
+                }
+
+        } while (1);
+
+        return bc;
+}
+
+/*
+ * Check if sg_io_hdr from user is allowed and valid
+ */
+static int
+bsg_validate_sghdr(request_queue_t *q, struct sg_io_hdr *hdr, int *rw)
+{
+        if (hdr->interface_id != 'S')
+                return -EINVAL;
+        if (hdr->cmd_len > BLK_MAX_CDB)
+                return -EINVAL;
+        if (hdr->dxfer_len > (q->max_sectors << 9))
+                return -EIO;
+
+        /*
+         * looks sane, if no data then it should be fine from our POV
+         */
+        if (!hdr->dxfer_len)
+                return 0;
+
+        switch (hdr->dxfer_direction) {
+                case SG_DXFER_TO_FROM_DEV:
+                case SG_DXFER_FROM_DEV:
+                        *rw = READ;
+                        break;
+                case SG_DXFER_TO_DEV:
+                        *rw = WRITE;
+                        break;
+                default:
+                        return -EINVAL;
+        }
+
+        return 0;
+}
+
+/*
+ * map sg_io_hdr to a request. for scatter-gather sg_io_hdr, we map
+ * each segment to a bio and string multiple bio's to the request
+ */
+static struct request *
+bsg_map_hdr(struct bsg_device *bd, int rw, struct sg_io_hdr *hdr)
+{
+        request_queue_t *q = bd->queue;
+        struct sg_iovec iov;
+        struct sg_iovec __user *u_iov;
+        struct request *rq;
+        int ret, i = 0;
+
+        dprintk("map hdr %p/%d/%d\n", hdr->dxferp, hdr->dxfer_len,
+                                        hdr->iovec_count);
+
+        ret = bsg_validate_sghdr(q, hdr, &rw);
+        if (ret)
+                return ERR_PTR(ret);
+
+        /*
+         * map scatter-gather elements seperately and string them to request
+         */
+        rq = blk_get_request(q, rw, GFP_KERNEL);
+        ret = blk_fill_sghdr_rq(q, rq, hdr, test_bit(BSG_F_WRITE_PERM,
+                                &bd->flags));
+        if (ret) {
+                blk_put_request(rq);
+                return ERR_PTR(ret);
+        }
+
+        if (!hdr->iovec_count) {
+                ret = blk_rq_map_user(q, rq, hdr->dxferp, hdr->dxfer_len);
+                if (ret)
+                        goto out;
+        }
+
+        u_iov = hdr->dxferp;
+        for (ret = 0, i = 0; i < hdr->iovec_count; i++, u_iov++) {
+                if (copy_from_user(&iov, u_iov, sizeof(iov))) {
+                        ret = -EFAULT;
+                        break;
+                }
+
+                if (!iov.iov_len || !iov.iov_base) {
+                        ret = -EINVAL;
+                        break;
+                }
+
+                ret = blk_rq_map_user(q, rq, iov.iov_base, iov.iov_len);
+                if (ret)
+                        break;
+        }
+
+        /*
+         * bugger, cleanup
+         */
+        if (ret) {
+out:
+                dprintk("failed map at %d: %d\n", i, ret);
+                blk_unmap_sghdr_rq(rq, hdr);
+                rq = ERR_PTR(ret);
+        }
+
+        return rq;
+}
+
+/*
+ * async completion call-back from the block layer, when scsi/ide/whatever
+ * calls end_that_request_last() on a request
+ */
+static void bsg_rq_end_io(struct request *rq, int uptodate)
+{
+        struct bsg_command *bc = rq->end_io_data;
+        struct bsg_device *bd = bc->bd;
+        unsigned long flags;
+
+        dprintk("%s: finished rq %p bio %p, bc %p offset %ld stat %d\n",
+                        bd->name, rq, bc, bc->bio, bc - bd->cmd_map, uptodate);
+
+        bc->hdr.duration = jiffies_to_msecs(jiffies - bc->hdr.duration);
+
+        spin_lock_irqsave(&bd->lock, flags);
+        list_del(&bc->list);
+        bsg_add_done_cmd(bd, bc);
+        spin_unlock_irqrestore(&bd->lock, flags);
+}
+
+/*
+ * do final setup of a 'bc' and submit the matching 'rq' to the block
+ * layer for io
+ */
+static void bsg_add_command(struct bsg_device *bd, request_queue_t *q,
+                            struct bsg_command *bc, struct request *rq)
+{
+        rq->sense = bc->sense;
+        rq->sense_len = 0;
+
+        /*
+         * add bc command to busy queue and submit rq for io
+         */
+        bc->rq = rq;
+        bc->bio = rq->bio;
+        bc->hdr.duration = jiffies;
+        spin_lock_irq(&bd->lock);
+        list_add_tail(&bc->list, &bd->busy_list);
+        spin_unlock_irq(&bd->lock);
+
+        dprintk("%s: queueing rq %p, bc %p\n", bd->name, rq, bc);
+
+        rq->end_io_data = bc;
+        blk_execute_rq_nowait(q, bd->disk, rq, 1, bsg_rq_end_io);
+}
+
+static inline struct bsg_command *bsg_next_done_cmd(struct bsg_device *bd)
+{
+        struct bsg_command *bc = NULL;
+
+        spin_lock_irq(&bd->lock);
+        if (bd->done_cmds) {
+                bc = list_entry_bc(bd->done_list.next);
+                bsg_del_done_cmd(bd, bc);
+        }
+        spin_unlock_irq(&bd->lock);
+
+        return bc;
+}
+
+/*
+ * Get a finished command from the done list
+ */
+static struct bsg_command *__bsg_get_done_cmd(struct bsg_device *bd, int state)
+{
+        struct bsg_command *bc;
+        int ret;
+
+        do {
+                bc = bsg_next_done_cmd(bd);
+                if (bc)
+                        break;
+
+                ret = bsg_io_schedule(bd, state);
+                if (ret) {
+                        bc = ERR_PTR(ret);
+                        break;
+                }
+        } while (1);
+
+        dprintk("%s: returning done %p\n", bd->name, bc);
+
+        return bc;
+}
+
+static struct bsg_command *
+bsg_get_done_cmd(struct bsg_device *bd, const struct iovec *iov)
+{
+        return __bsg_get_done_cmd(bd, TASK_INTERRUPTIBLE);
+}
+
+static struct bsg_command *
+bsg_get_done_cmd_nosignals(struct bsg_device *bd)
+{
+        return __bsg_get_done_cmd(bd, TASK_UNINTERRUPTIBLE);
+}
+
+static int bsg_complete_all_commands(struct bsg_device *bd)
+{
+        struct bsg_command *bc;
+        int ret, tret;
+
+        dprintk("%s: entered\n", bd->name);
+
+        set_bit(BSG_F_BLOCK, &bd->flags);
+
+        /*
+         * wait for all commands to complete
+         */
+        ret = 0;
+        do {
+                ret = bsg_io_schedule(bd, TASK_UNINTERRUPTIBLE);
+                /*
+                 * look for -ENODATA specifically -- we'll sometimes get
+                 * -ERESTARTSYS when we've taken a signal, but we can't
+                 * return until we're done freeing the queue, so ignore
+                 * it.  The signal will get handled when we're done freeing
+                 * the bsg_device.
+                 */
+        } while (ret != -ENODATA);
+
+        /*
+         * discard done commands
+         */
+        ret = 0;
+        do {
+                bc = bsg_get_done_cmd_nosignals(bd);
+
+                /*
+                 * we _must_ complete before restarting, because
+                 * bsg_release can't handle this failing.
+                 */
+                if (PTR_ERR(bc) == -ERESTARTSYS)
+                        continue;
+                if (IS_ERR(bc)) {
+                        ret = PTR_ERR(bc);
+                        break;
+                }
+
+                tret = blk_complete_sghdr_rq(bc->rq, &bc->hdr, bc->bio);
+                if (!ret)
+                        ret = tret;
+
+                bsg_free_command(bc);
+        } while (1);
+
+        return ret;
+}
+
+typedef struct bsg_command *(*bsg_command_callback)(struct bsg_device *bd, const struct iovec *iov);
+
+static ssize_t
+__bsg_read(char __user *buf, size_t count, bsg_command_callback get_bc,
+           struct bsg_device *bd, const struct iovec *iov, ssize_t *bytes_read)
+{
+        struct bsg_command *bc;
+        int nr_commands, ret;
+
+        if (count % sizeof(struct sg_io_hdr))
+                return -EINVAL;
+
+        ret = 0;
+        nr_commands = count / sizeof(struct sg_io_hdr);
+        while (nr_commands) {
+                bc = get_bc(bd, iov);
+                if (IS_ERR(bc)) {
+                        ret = PTR_ERR(bc);
+                        break;
+                }
+
+                /*
+                 * this is the only case where we need to copy data back
+                 * after completing the request. so do that here,
+                 * bsg_complete_work() cannot do that for us
+                 */
+                ret = blk_complete_sghdr_rq(bc->rq, &bc->hdr, bc->bio);
+
+                if (copy_to_user(buf, (char *) &bc->hdr, sizeof(bc->hdr)))
+                        ret = -EFAULT;
+
+                bsg_free_command(bc);
+
+                if (ret)
+                        break;
+
+                buf += sizeof(struct sg_io_hdr);
+                *bytes_read += sizeof(struct sg_io_hdr);
+                nr_commands--;
+        }
+
+        return ret;
+}
+
+static inline void bsg_set_block(struct bsg_device *bd, struct file *file)
+{
+        if (file->f_flags & O_NONBLOCK)
+                clear_bit(BSG_F_BLOCK, &bd->flags);
+        else
+                set_bit(BSG_F_BLOCK, &bd->flags);
+}
+
+static inline void bsg_set_write_perm(struct bsg_device *bd, struct file *file)
+{
+        if (file->f_mode & FMODE_WRITE)
+                set_bit(BSG_F_WRITE_PERM, &bd->flags);
+        else
+                clear_bit(BSG_F_WRITE_PERM, &bd->flags);
+}
+
+static inline int err_block_err(int ret)
+{
+        if (ret && ret != -ENOSPC && ret != -ENODATA && ret != -EAGAIN)
+                return 1;
+
+        return 0;
+}
+
+static ssize_t
+bsg_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
+{
+        struct bsg_device *bd = file->private_data;
+        int ret;
+        ssize_t bytes_read;
+
+        dprintk("%s: read %lu bytes\n", bd->name, count);
+
+        bsg_set_block(bd, file);
+        bytes_read = 0;
+        ret = __bsg_read(buf, count, bsg_get_done_cmd,
+                        bd, NULL, &bytes_read);
+        *ppos = bytes_read;
+
+        if (!bytes_read || (bytes_read && err_block_err(ret)))
+                bytes_read = ret;
+
+        return bytes_read;
+}
+
+static ssize_t __bsg_write(struct bsg_device *bd, const char __user *buf,
+                           size_t count, ssize_t *bytes_read)
+{
+        struct bsg_command *bc;
+        struct request *rq;
+        int ret, nr_commands;
+
+        if (count % sizeof(struct sg_io_hdr))
+                return -EINVAL;
+
+        nr_commands = count / sizeof(struct sg_io_hdr);
+        rq = NULL;
+        bc = NULL;
+        ret = 0;
+        while (nr_commands) {
+                request_queue_t *q = bd->queue;
+                int rw = READ;
+
+                bc = bsg_get_command(bd);
+                if (!bc)
+                        break;
+                if (IS_ERR(bc)) {
+                        ret = PTR_ERR(bc);
+                        bc = NULL;
+                        break;
+                }
+
+                bc->uhdr = (struct sg_io_hdr __user *) buf;
+                if (copy_from_user(&bc->hdr, buf, sizeof(bc->hdr))) {
+                        ret = -EFAULT;
+                        break;
+                }
+
+                /*
+                 * get a request, fill in the blanks, and add to request queue
+                 */
+                rq = bsg_map_hdr(bd, rw, &bc->hdr);
+                if (IS_ERR(rq)) {
+                        ret = PTR_ERR(rq);
+                        rq = NULL;
+                        break;
+                }
+
+                bsg_add_command(bd, q, bc, rq);
+                bc = NULL;
+                rq = NULL;
+                nr_commands--;
+                buf += sizeof(struct sg_io_hdr);
+                *bytes_read += sizeof(struct sg_io_hdr);
+        }
+
+        if (rq)
+                blk_unmap_sghdr_rq(rq, &bc->hdr);
+        if (bc)
+                bsg_free_command(bc);
+
+        return ret;
+}
+
+static ssize_t
+bsg_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
+{
+        struct bsg_device *bd = file->private_data;
+        ssize_t bytes_read;
+        int ret;
+
+        dprintk("%s: write %lu bytes\n", bd->name, count);
+
+        bsg_set_block(bd, file);
+        bsg_set_write_perm(bd, file);
+
+        bytes_read = 0;
+        ret = __bsg_write(bd, buf, count, &bytes_read);
+        *ppos = bytes_read;
+
+        /*
+         * return bytes written on non-fatal errors
+         */
+        if (!bytes_read || (bytes_read && err_block_err(ret)))
+                bytes_read = ret;
+
+        dprintk("%s: returning %lu\n", bd->name, bytes_read);
+        return bytes_read;
+}
+
+static void bsg_free_device(struct bsg_device *bd)
+{
+        if (bd->cmd_map)
+                free_pages((unsigned long) bd->cmd_map, BSG_CMDS_PAGE_ORDER);
+
+        kfree(bd->cmd_bitmap);
+        kfree(bd);
+}
+
+static struct bsg_device *bsg_alloc_device(void)
+{
+        struct bsg_command *cmd_map;
+        unsigned long *cmd_bitmap;
+        struct bsg_device *bd;
+        int bits;
+
+        bd = kzalloc(sizeof(struct bsg_device), GFP_KERNEL);
+        if (unlikely(!bd))
+                return NULL;
+
+        spin_lock_init(&bd->lock);
+
+        bd->max_queue = BSG_CMDS;
+
+        bits = (BSG_CMDS / BSG_CMDS_PER_LONG) + 1;
+        cmd_bitmap = kzalloc(bits * sizeof(unsigned long), GFP_KERNEL);
+        if (!cmd_bitmap)
+                goto out_free_bd;
+        bd->cmd_bitmap = cmd_bitmap;
+
+        cmd_map = (void *) __get_free_pages(GFP_KERNEL | __GFP_ZERO,
+                                                BSG_CMDS_PAGE_ORDER);
+        if (!cmd_map)
+                goto out_free_bitmap;
+        bd->cmd_map = cmd_map;
+
+        INIT_LIST_HEAD(&bd->busy_list);
+        INIT_LIST_HEAD(&bd->done_list);
+        INIT_HLIST_NODE(&bd->dev_list);
+
+        init_waitqueue_head(&bd->wq_free);
+        init_waitqueue_head(&bd->wq_done);
+        return bd;
+
+out_free_bitmap:
+        kfree(cmd_bitmap);
+out_free_bd:
+        kfree(bd);
+        return NULL;
+}
+
+static int bsg_put_device(struct bsg_device *bd)
+{
+        int ret = 0;
+
+        mutex_lock(&bsg_mutex);
+
+        if (!atomic_dec_and_test(&bd->ref_count))
+                goto out;
+
+        dprintk("%s: tearing down\n", bd->name);
+
+        /*
+         * close can always block
+         */
+        set_bit(BSG_F_BLOCK, &bd->flags);
+
+        /*
+         * correct error detection baddies here again. it's the responsibility
+         * of the app to properly reap commands before close() if it wants
+         * fool-proof error detection
+         */
+        ret = bsg_complete_all_commands(bd);
+
+        blk_put_queue(bd->queue);
+        hlist_del(&bd->dev_list);
+        bsg_free_device(bd);
+out:
+        mutex_unlock(&bsg_mutex);
+        return ret;
+}
+
+static struct bsg_device *bsg_add_device(struct inode *inode,
+                                         struct gendisk *disk,
+                                         struct file *file)
+{
+        struct bsg_device *bd = NULL;
+#ifdef BSG_DEBUG
+        unsigned char buf[32];
+#endif
+
+        bd = bsg_alloc_device();
+        if (!bd)
+                return ERR_PTR(-ENOMEM);
+
+        bd->disk = disk;
+        bd->queue = disk->queue;
+        kobject_get(&disk->queue->kobj);
+        bsg_set_block(bd, file);
+
+        atomic_set(&bd->ref_count, 1);
+        bd->minor = iminor(inode);
+        mutex_lock(&bsg_mutex);
+        hlist_add_head(&bd->dev_list,&bsg_device_list[bsg_list_idx(bd->minor)]);
+
+        strncpy(bd->name, disk->disk_name, sizeof(bd->name) - 1);
+        dprintk("bound to <%s>, max queue %d\n",
+                format_dev_t(buf, i->i_rdev), bd->max_queue);
+
+        mutex_unlock(&bsg_mutex);
+        return bd;
+}
+
+static struct bsg_device *__bsg_get_device(int minor)
+{
+        struct hlist_head *list = &bsg_device_list[bsg_list_idx(minor)];
+        struct bsg_device *bd = NULL;
+        struct hlist_node *entry;
+
+        mutex_lock(&bsg_mutex);
+
+        hlist_for_each(entry, list) {
+                bd = hlist_entry(entry, struct bsg_device, dev_list);
+                if (bd->minor == minor) {
+                        atomic_inc(&bd->ref_count);
+                        break;
+                }
+
+                bd = NULL;
+        }
+
+        mutex_unlock(&bsg_mutex);
+        return bd;
+}
+
+static struct bsg_device *bsg_get_device(struct inode *inode, struct file *file)
+{
+        struct bsg_device *bd = __bsg_get_device(iminor(inode));
+        struct bsg_class_device *bcd, *__bcd;
+
+        if (bd)
+                return bd;
+
+        /*
+         * find the class device
+         */
+        bcd = NULL;
+        mutex_lock(&bsg_mutex);
+        list_for_each_entry(__bcd, &bsg_class_list, list) {
+                if (__bcd->minor == iminor(inode)) {
+                        bcd = __bcd;
+                        break;
+                }
+        }
+        mutex_unlock(&bsg_mutex);
+
+        if (!bcd)
+                return ERR_PTR(-ENODEV);
+
+        return bsg_add_device(inode, bcd->disk, file);
+}
+
+static int bsg_open(struct inode *inode, struct file *file)
+{
+        struct bsg_device *bd = bsg_get_device(inode, file);
+
+        if (IS_ERR(bd))
+                return PTR_ERR(bd);
+
+        file->private_data = bd;
+        return 0;
+}
+
+static int bsg_release(struct inode *inode, struct file *file)
+{
+        struct bsg_device *bd = file->private_data;
+
+        file->private_data = NULL;
+        return bsg_put_device(bd);
+}
+
+static unsigned int bsg_poll(struct file *file, poll_table *wait)
+{
+        struct bsg_device *bd = file->private_data;
+        unsigned int mask = 0;
+
+        poll_wait(file, &bd->wq_done, wait);
+        poll_wait(file, &bd->wq_free, wait);
+
+        spin_lock_irq(&bd->lock);
+        if (!list_empty(&bd->done_list))
+                mask |= POLLIN | POLLRDNORM;
+        if (bd->queued_cmds >= bd->max_queue)
+                mask |= POLLOUT;
+        spin_unlock_irq(&bd->lock);
+
+        return mask;
+}
+
+static int
+bsg_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
+          unsigned long arg)
+{
+        struct bsg_device *bd = file->private_data;
+        int __user *uarg = (int __user *) arg;
+
+        if (!bd)
+                return -ENXIO;
+
+        switch (cmd) {
+                /*
+                 * our own ioctls
+                 */
+        case SG_GET_COMMAND_Q:
+                return put_user(bd->max_queue, uarg);
+                case SG_SET_COMMAND_Q: {
+                int queue;
+
+                if (get_user(queue, uarg))
+                        return -EFAULT;
+                if (queue > BSG_CMDS || queue < 1)
+                        return -EINVAL;
+
+                bd->max_queue = queue;
+                return 0;
+        }
+
+        /*
+         * SCSI/sg ioctls
+         */
+        case SG_GET_VERSION_NUM:
+        case SCSI_IOCTL_GET_IDLUN:
+        case SCSI_IOCTL_GET_BUS_NUMBER:
+        case SG_SET_TIMEOUT:
+        case SG_GET_TIMEOUT:
+        case SG_GET_RESERVED_SIZE:
+        case SG_SET_RESERVED_SIZE:
+        case SG_EMULATED_HOST:
+        case SG_IO:
+        case SCSI_IOCTL_SEND_COMMAND: {
+                void __user *uarg = (void __user *) arg;
+                return scsi_cmd_ioctl(file, bd->disk, cmd, uarg);
+        }
+        /*
+         * block device ioctls
+         */
+        default:
+#if 0
+                return ioctl_by_bdev(bd->bdev, cmd, arg);
+#else
+                return -ENOTTY;
+#endif
+        }
+}
+
+static struct file_operations bsg_fops = {
+        .read           =       bsg_read,
+        .write          =       bsg_write,
+        .poll           =       bsg_poll,
+        .open           =       bsg_open,
+        .release        =       bsg_release,
+        .ioctl          =       bsg_ioctl,
+        .owner          =       THIS_MODULE,
+};
+
+void bsg_unregister_disk(struct gendisk *disk)
+{
+        struct bsg_class_device *bcd = &disk->bsg_dev;
+
+        if (!bcd->class_dev)
+                return;
+
+        mutex_lock(&bsg_mutex);
+        sysfs_remove_link(&bcd->disk->queue->kobj, "bsg");
+        class_device_destroy(bsg_class, MKDEV(BSG_MAJOR, bcd->minor));
+        bcd->class_dev = NULL;
+        list_del_init(&bcd->list);
+        mutex_unlock(&bsg_mutex);
+}
+
+int bsg_register_disk(struct gendisk *disk)
+{
+        request_queue_t *q = disk->queue;
+        struct bsg_class_device *bcd;
+        dev_t dev;
+
+        /*
+         * we need a proper transport to send commands, not a stacked device
+         */
+        if (!q->request_fn)
+                return 0;
+
+        bcd = &disk->bsg_dev;
+        memset(bcd, 0, sizeof(*bcd));
+        INIT_LIST_HEAD(&bcd->list);
+
+        mutex_lock(&bsg_mutex);
+        dev = MKDEV(BSG_MAJOR, bsg_device_nr);
+        bcd->minor = bsg_device_nr;
+        bsg_device_nr++;
+        bcd->disk = disk;
+        bcd->class_dev = class_device_create(bsg_class, NULL, dev, bcd->dev, "%s", disk->disk_name);
+        list_add_tail(&bcd->list, &bsg_class_list);
+        sysfs_create_link(&q->kobj, &bcd->class_dev->kobj, "bsg");
+        mutex_unlock(&bsg_mutex);
+        return 0;
+}
+
+static int __init bsg_init(void)
+{
+        int ret, i;
+
+        for (i = 0; i < BSG_LIST_SIZE; i++)
+                INIT_HLIST_HEAD(&bsg_device_list[i]);
+
+        bsg_class = class_create(THIS_MODULE, "bsg");
+        if (IS_ERR(bsg_class))
+                return PTR_ERR(bsg_class);
+
+        ret = register_chrdev(BSG_MAJOR, "bsg", &bsg_fops);
+        if (ret) {
+                class_destroy(bsg_class);
+                return ret;
+        }
+
+        printk(KERN_INFO "%s loaded\n", bsg_version);
+        return 0;
+}
+
+MODULE_AUTHOR("Jens Axboe");
+MODULE_DESCRIPTION("Block layer SGSI generic (sg) driver");
+MODULE_LICENSE("GPL");
+
+subsys_initcall(bsg_init);