Jens Axboe <[email protected]> wrote:
>
> After all that SG_IO and cdrecord talk, I decided to brush off the bsg
> driver I wrote some time ago. Basically this is a full (aims to be at
> least, probably still some minor bits missing) SG v3 interface. It
> supports both SG_IO (which we just pass through for now), as well as
> read/write and readv/writev of sg_io_hdr structures.
>
> What's new in this area is that the bsg character device is closely tied
> to the block device. This relationsship is depicted in sysfs. bsg
> devices will show up in /sys/class/bsg/<devname>, and there is a link
> from /sys/block/<devname>/queue/bsg to that directory. With some
> udev/hotplug magic, it should create device nodes for you automatically.
>
> +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);
It would be strange for this assertion to trigger.
> +
Three free tabs!
> + bd->queued_cmds++;
> + free_nr += ffz(*map);
Can't find_first_bit() be used here?
> + __set_bit(free_nr, bd->cmd_bitmap);
I'm suspecting that the whole cmd_bitmap thing could use the bitmap API?
> +static inline int bsg_io_schedule(struct bsg_device *bd, int state)
This large function has four callers...
Needs a comment block, please.
> + 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;
> + }
> +
> + spin_unlock_irq(&bd->lock);
> + prepare_to_wait(&bd->wq_done, &wait, state);
> + io_schedule();
> + finish_wait(&bd->wq_done, &wait);
> +
> + if ((state == TASK_INTERRUPTIBLE) && signal_pending(current))
> + ret = -ERESTARTSYS;
Racy? Should the the prepare_to_wait() happen before the lock is dropped?
> +/*
> + * 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);
OK. I trust you've tested that this all does the right thing when it's sent a
signal?
> +/*
> + * 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;
'S'? What does that mean?
> +/*
> + * 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(request_queue_t *q, int rw, struct sg_io_hdr *hdr)
> +{
> + struct sg_iovec iov;
> + struct sg_iovec __user *u_iov;
> + struct request *rq;
> + struct bio *bio;
> + 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_WAIT);
GFP_NOIO would be more meaningful.
> + 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++) {
> + int to_vm = rw == READ;
> + unsigned long uaddr;
> +
> + if (copy_from_user(&iov, u_iov, sizeof(iov))) {
If we can do copy_from_user() here then that blk_get_request() could have used
GFP_KERNEL.
> + ret = -EFAULT;
> + break;
> + }
> +
> + if (!iov.iov_len || !iov.iov_base) {
> + ret = -EINVAL;
> + break;
> + }
> +
> + uaddr = (unsigned long) iov.iov_base;
> + if (!(uaddr & queue_dma_alignment(q))
> + && !(iov.iov_len & queue_dma_alignment(q)))
hm, queue_dma_alignment() is an ugly thing. queue_dma_aligned(q, addr) would
be nicer.
> +/*
> + * 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;
> +
> + rq->rq_disk = bd->disk;
> + rq->end_io_data = bc;
> + rq->end_io = bsg_rq_end_io;
> +
> + /*
> + * 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);
> +
> + elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 1);
> + generic_unplug_device(q);
If you expand the two above statements you get:
spin_lock_irqsave(q->queue_lock, flags);
__elv_add_request(q, rq, where, plug);
spin_unlock_irqrestore(q->queue_lock, flags);
spin_lock_irq(q->queue_lock);
__generic_unplug_device(q);
spin_unlock_irq(q->queue_lock);
which is a bit sad.
> +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
> + */
Would it be useful to reap the completed commands earlier? While their
predecessors are still in flight?
> + 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 (PTR_ERR(bc)) {
You wanted IS_ERR(), I think.
> + ret = PTR_ERR(bc);
> + break;
> + }
> +
> + /*
> + * If we get any other error, bd->queued_cmds is wrong.
> + */
> + BUG_ON(IS_ERR(bc));
If so, that can't trigger.
> +
> +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);
yowch, this sg_io_hdr thing is cast in stone, isn't it?
> +
> +#define err_block_err(ret) \
> + ((ret) && (ret) != -ENOSPC && (ret) != -ENODATA && (ret) != -EAGAIN)
Make this a function?
> +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;
> +
> + if (unlikely(!bd))
> + return -ENXIO;
Is that possible?
> +static ssize_t
> +bsg_readv(struct file *file, const struct iovec *iov, unsigned long nr_segs,
> + loff_t *ppos)
> +{
> + struct bsg_device *bd = file->private_data;
> + int ret = 0;
> + ssize_t bytes_read = 0;
> +
> + if (unlikely(!bd))
> + return -ENXIO;
No, looking at bsg_open() I don't think it is.
> +static int bsg_writev_validate_iovec(const struct iovec *iov)
> +{
> + struct sg_io_hdr hdr;
> +
> + dprintk("iov[0] = {%p, %Zu}, sizeof(struct sg_io_hdr) = %Zu\n",
> + iov[0].iov_base, iov[0].iov_len, sizeof(struct sg_io_hdr));
> + if (iov[0].iov_len != sizeof(struct sg_io_hdr))
> + return -EINVAL;
> +
> + /*
> + * I really don't like doing this copy twice, but I don't see a good
> + * way around it...
> + */
> + if (copy_from_user(&hdr, iov[0].iov_base, sizeof(struct sg_io_hdr)))
> + return -EFAULT;
Is this function temporary? If not, you might want to optimise out the
double copy_from_user().
> +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);
> + bd->cmd_bitmap = NULL;
> + bd->disk = NULL;
> + bd->queue = NULL;
> + bd->cmd_map = NULL;
> + kfree(bd);
> +}
Those assignments-to-NULL are a bit unnecessary - CONFIG_DEBUG_SLAB will catch
use-after-frees (and setting them to NULL might actively hide bugs).
> +static struct bsg_device *bsg_alloc_device(void)
> +{
> + struct bsg_device *bd = kmalloc(sizeof(struct bsg_device), GFP_KERNEL);
> + struct bsg_command *cmd_map;
> + unsigned long *cmd_bitmap;
> + int bits;
> +
> + if (unlikely(!bd))
> + return NULL;
> +
> + memset(bd, 0, sizeof(struct bsg_device));
kzalloc().
> + spin_lock_init(&bd->lock);
> +
> + bd->max_queue = BSG_CMDS;
> +
> + bits = (BSG_CMDS / BSG_CMDS_PER_LONG) + 1;
> + cmd_bitmap = kmalloc(bits * sizeof(unsigned long), GFP_KERNEL);
kzalloc().
> + if (!cmd_bitmap)
> + goto out_free_bd;
> + bd->cmd_bitmap = cmd_bitmap;
> +
> + cmd_map = (struct bsg_command *) __get_free_pages(GFP_KERNEL,
> + BSG_CMDS_PAGE_ORDER);
__GFP_ZERO, perhaps.
> +static int bsg_put_device(struct bsg_device *bd)
> +{
> + int ret;
> +
> + if (!atomic_dec_and_test(&bd->ref_count))
> + return 0;
> +
> + mutex_lock(&bsg_mutex);
Isn't this racy? Someone can still find this device on bsg_device_list[]
> + 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_cleanup_queue(bd->queue);
> + hlist_del(&bd->dev_list);
> + bsg_free_device(bd);
> + 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
> + int ret;
> +
> + mutex_lock(&bsg_mutex);
> +
> + ret = -ENOMEM;
> + bd = bsg_alloc_device();
This can be called outside the lock.
Can this driver be used for pagecache or swap I/O? If so, doing GFP_KERNEL
allocations while holding the lock might be a problem. (OK, probably it's not
deadlocky, but still - do it outside the lock).
> + if (!bd)
> + goto out;
> +
> + bd->disk = disk;
> + bd->queue = disk->queue;
> + atomic_inc(&disk->queue->refcnt);
> + bsg_set_block(bd, file);
> +
> + atomic_set(&bd->ref_count, 1);
> + bd->minor = iminor(inode);
> + hlist_add_head(&bd->dev_list,&bsg_device_list[bsg_list_idx(bd->minor)]);
> +
> + strncpy(bd->name, disk->disk_name, sizeof(bd->name));
This might not null-terminate bd->name.
> +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:
The switch's body could be moved a tabstop to the left.
> +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);
Again, we're probably doing GFP_KERNEL allocations with bsg_mutex held.
Please check.
> +EXPORT_SYMBOL(blk_fill_sghdr_rq);
GPL?
> +
> +/*
> + * unmap a request that was previously mapped to this sg_io_hdr. handles
> + * both sg and non-sg sg_io_hdr.
> + */
> +int blk_unmap_sghdr_rq(struct request *rq, struct sg_io_hdr *hdr)
> +{
> + struct bio *bio = rq->bio;
> +
> + /*
> + * also releases request
> + */
> + if (!hdr->iovec_count)
> + return blk_rq_unmap_user(bio, hdr->dxfer_len);
> +
> + while ((bio = rq->bio)) {
> + rq->bio = bio->bi_next;
> + bio->bi_next = NULL;
> +
> + bio_unmap_user(bio);
> + }
rq_for_each_bio()?
> +
> +int blk_complete_sghdr_rq(struct request *rq, struct sg_io_hdr *hdr,
> + struct bio *bio)
> +{
> + /*
> + * fill in all the output members
> + */
> + hdr->status = rq->errors & 0xff;
> + hdr->masked_status = status_byte(rq->errors);
> + hdr->msg_status = msg_byte(rq->errors);
> + hdr->host_status = host_byte(rq->errors);
> + hdr->driver_status = driver_byte(rq->errors);
> + hdr->info = 0;
> + if (hdr->masked_status || hdr->host_status || hdr->driver_status)
> + hdr->info |= SG_INFO_CHECK;
> + hdr->resid = rq->data_len;
> + hdr->sb_len_wr = 0;
> +
> + if (rq->sense_len && hdr->sbp) {
> + int len = min((unsigned int) hdr->mx_sb_len, rq->sense_len);
> +
> + if (!copy_to_user(hdr->sbp, rq->sense, len))
> + hdr->sb_len_wr = len;
No -EFAULT?
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