On Thursday 02 June 2016 13:25:00 Pranay Kr. Srivastava wrote: > When a timeout occurs or a recv fails, then > instead of abruplty killing nbd block device > wait for it's users to finish. > > This is more required when filesystem(s) like > ext2 or ext3 don't expect their buffer heads to > disappear while the filesystem is mounted. > > Each open of a nbd device is refcounted, while > the userland program [nbd-client] doing the > NBD_DO_IT ioctl would now wait for any other users > of this device before invalidating the nbd device. > > Signed-off-by: Pranay Kr. Srivastava <[email protected]> > --- > drivers/block/nbd.c | 58 > +++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 58 insertions(+) > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > index d1d898d..4da40dc 100644 > --- a/drivers/block/nbd.c > +++ b/drivers/block/nbd.c > @@ -70,10 +70,13 @@ struct nbd_device { > #if IS_ENABLED(CONFIG_DEBUG_FS) > struct dentry *dbg_dir; > #endif > + atomic_t inuse; > /* > *This is specifically for calling sock_shutdown, for now. > */ > struct work_struct ws_shutdown; > + struct kref users; > + struct completion user_completion; > }; > > #if IS_ENABLED(CONFIG_DEBUG_FS) > @@ -104,6 +107,7 @@ static DEFINE_SPINLOCK(nbd_lock); > * Shutdown function for nbd_dev work struct. > */ > static void nbd_ws_func_shutdown(struct work_struct *); > +static void nbd_kref_release(struct kref *); > > static inline struct device *nbd_to_dev(struct nbd_device *nbd) > { > @@ -682,6 +686,8 @@ static void nbd_reset(struct nbd_device *nbd) > nbd->flags = 0; > nbd->xmit_timeout = 0; > INIT_WORK(&nbd->ws_shutdown, nbd_ws_func_shutdown); > + init_completion(&nbd->user_completion); > + kref_init(&nbd->users); > queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue); > del_timer_sync(&nbd->timeout_timer); > } > @@ -815,6 +821,14 @@ static int __nbd_ioctl(struct block_device *bdev, struct > nbd_device *nbd, > kthread_stop(thread); > > sock_shutdown(nbd); > + /* > + * kref_init initializes with ref count as 1, > + * nbd_client, or the user-land program executing > + * this ioctl will make the refcount to 2[at least] > + * so subtracting 2 from refcount. > + */ > + kref_sub(&nbd->users, 2, nbd_kref_release);
Why don't you use a kref_put?
> + wait_for_completion(&nbd->user_completion);
> mutex_lock(&nbd->tx_lock);
> nbd_clear_que(nbd);
> kill_bdev(bdev);
> @@ -865,13 +879,56 @@ static int nbd_ioctl(struct block_device *bdev, fmode_t
> mode,
>
> return error;
> }
> +static void nbd_kref_release(struct kref *kref_users)
> +{
> + struct nbd_device *nbd = container_of(kref_users, struct nbd_device,
> + users);
Not indented to opening bracket.
> + pr_debug("Releasing kref [%s]\n", __func__);
> + atomic_set(&nbd->inuse, 0);
> + complete(&nbd->user_completion);
> +
> +}
> +
> +static int nbd_open(struct block_device *bdev, fmode_t mode)
> +{
> + struct nbd_device *nbd_dev = bdev->bd_disk->private_data;
> +
> + if (kref_get_unless_zero(&nbd_dev->users))
> + atomic_set(&nbd_dev->inuse, 1);
> +
> + pr_debug("Opening nbd_dev %s. Active users = %u\n",
> + bdev->bd_disk->disk_name,
> + atomic_read(&nbd_dev->users.refcount) - 1);
Indent to opening bracket.
> + return 0;
> +}
> +
> +static void nbd_release(struct gendisk *disk, fmode_t mode)
> +{
> + struct nbd_device *nbd_dev = disk->private_data;
> + /*
> + *kref_init initializes ref count to 1, so we
> + *we check for refcount to be 2 for a final put.
> + *
> + *kref needs to be re-initialized just here as the
> + *other process holding it must see the ref count as 2.
> + */
> + if (atomic_read(&nbd_dev->inuse))
> + kref_put(&nbd_dev->users, nbd_kref_release);
What is this inuse atomic for? Everyone that releases the nbd device
will need to execute a kref_put().
Best Regards,
Markus
> +
> + pr_debug("Closing nbd_dev %s. Active users = %u\n",
> + disk->disk_name,
> + atomic_read(&nbd_dev->users.refcount) - 1);
> +}
>
> static const struct block_device_operations nbd_fops = {
> .owner = THIS_MODULE,
> .ioctl = nbd_ioctl,
> .compat_ioctl = nbd_ioctl,
> + .open = nbd_open,
> + .release = nbd_release
> };
>
> +
> static void nbd_ws_func_shutdown(struct work_struct *ws_nbd)
> {
> struct nbd_device *nbd_dev = container_of(ws_nbd, struct nbd_device,
> @@ -1107,6 +1164,7 @@ static int __init nbd_init(void)
> disk->fops = &nbd_fops;
> disk->private_data = &nbd_dev[i];
> sprintf(disk->disk_name, "nbd%d", i);
> + atomic_set(&nbd_dev[i].inuse, 0);
> nbd_reset(&nbd_dev[i]);
> add_disk(disk);
> }
>
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