Re: [PATCH 10/10] nbd: Create size change events for userspace

[Markus Pargmann]

On Mon, Jul 27, 2015 at 09:12:56AM +0200, Markus Pargmann wrote:
> The userspace needs to know when nbd devices are ready for use.
> Currently no events are created for the userspace which doesn't work for
> systemd.
> 
> See the discussion here: https://github.com/systemd/systemd/pull/358
> 
> This patch uses a central point to setup the nbd-internal sizes. A ioctl
> to set a size does not lead to a visible size change. The size of the
> block device will be kept at 0 until nbd is connected. As soon as it
> connects, the size will be changed to the real value and a uevent is
> created. When disconnecting, the blockdevice is set to 0 size and
> another uevent is generated.
> 
> Signed-off-by: Markus Pargmann <mpa@xxxxxxxxxxxxxx>
> ---
>  drivers/block/nbd.c | 74 ++++++++++++++++++++++++++++++++++++++---------------
>  1 file changed, 54 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 1176a3b27a7e..95eb2904c324 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -97,6 +97,11 @@ static inline struct device *nbd_to_dev(struct nbd_device *nbd)
>  	return disk_to_dev(nbd->disk);
>  }
>  
> +static bool nbd_is_connected(struct nbd_device *nbd)
> +{
> +	return !!nbd->task_recv;
> +}
> +
>  static const char *nbdcmd_to_ascii(int cmd)
>  {
>  	switch (cmd) {
> @@ -109,6 +114,43 @@ static const char *nbdcmd_to_ascii(int cmd)
>  	return "invalid";
>  }
>  
> +static int nbd_size_clear(struct nbd_device *nbd, struct block_device *bdev)
> +{
> +	bdev->bd_inode->i_size = 0;
> +	set_blocksize(bdev, 0);
> +	set_capacity(nbd->disk, 0);
> +	kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
> +
> +	return 0;
> +}
> +
> +static int nbd_size_update(struct nbd_device *nbd, struct block_device *bdev)
> +{
> +	int ret;
> +
> +	if (!nbd_is_connected(nbd))
> +		return 0;
> +
> +	ret = set_blocksize(bdev, nbd->blksize);
> +	if (ret)
> +		return ret;
> +
> +	bdev->bd_inode->i_size = nbd->bytesize;
> +	set_capacity(nbd->disk, nbd->bytesize >> 9);
> +	kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
> +
> +	return 0;
> +}
> +
> +static int nbd_size_set(struct nbd_device *nbd, struct block_device *bdev,
> +			int blocksize, int nr_blocks)
> +{
> +	nbd->blksize = blocksize;
> +	nbd->bytesize = blocksize * nr_blocks;
> +
> +	return nbd_size_update(nbd, bdev);
> +}
> +
>  static void nbd_end_request(struct nbd_device *nbd, struct request *req)
>  {
>  	int error = req->errors ? -EIO : 0;
> @@ -399,7 +441,7 @@ static struct device_attribute pid_attr = {
>  	.show = pid_show,
>  };
>  
> -static int nbd_thread_recv(struct nbd_device *nbd)
> +static int nbd_thread_recv(struct nbd_device *nbd, struct block_device *bdev)
>  {
>  	struct request *req;
>  	int ret;
> @@ -417,6 +459,8 @@ static int nbd_thread_recv(struct nbd_device *nbd)
>  		return ret;
>  	}
>  
> +	nbd_size_update(nbd, bdev);
> +
>  	while (1) {
>  		req = nbd_read_stat(nbd);
>  		if (IS_ERR(req)) {
> @@ -427,6 +471,8 @@ static int nbd_thread_recv(struct nbd_device *nbd)
>  		nbd_end_request(nbd, req);
>  	}
>  
> +	nbd_size_clear(nbd, bdev);
> +
>  	device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
>  
>  	nbd->task_recv = NULL;
> @@ -681,19 +727,14 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>  	}
>  
>  	case NBD_SET_BLKSIZE:
> -		nbd->blksize = arg;
> -		nbd->bytesize &= ~(nbd->blksize-1);
> -		bdev->bd_inode->i_size = nbd->bytesize;
> -		set_blocksize(bdev, nbd->blksize);
> -		set_capacity(nbd->disk, nbd->bytesize >> 9);
> -		return 0;
> +		return nbd_size_set(nbd, bdev, arg, nbd->bytesize / arg);

This does not work for 32bit systems. Have to use do_div() for this.
Will fix that for the next version.

Best regards,

Markus

>  
>  	case NBD_SET_SIZE:
> -		nbd->bytesize = arg & ~(nbd->blksize-1);
> -		bdev->bd_inode->i_size = nbd->bytesize;
> -		set_blocksize(bdev, nbd->blksize);
> -		set_capacity(nbd->disk, nbd->bytesize >> 9);
> -		return 0;
> +		return nbd_size_set(nbd, bdev, nbd->blksize,
> +				    arg / nbd->blksize);
> +
> +	case NBD_SET_SIZE_BLOCKS:
> +		return nbd_size_set(nbd, bdev, nbd->blksize, arg);
>  
>  	case NBD_SET_TIMEOUT:
>  		nbd->xmit_timeout = arg * HZ;
> @@ -709,13 +750,6 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>  		nbd->flags = arg;
>  		return 0;
>  
> -	case NBD_SET_SIZE_BLOCKS:
> -		nbd->bytesize = ((u64) arg) * nbd->blksize;
> -		bdev->bd_inode->i_size = nbd->bytesize;
> -		set_blocksize(bdev, nbd->blksize);
> -		set_capacity(nbd->disk, nbd->bytesize >> 9);
> -		return 0;
> -
>  	case NBD_DO_IT: {
>  		struct task_struct *thread;
>  		struct socket *sock;
> @@ -746,7 +780,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>  		}
>  
>  		nbd_dev_dbg_init(nbd);
> -		error = nbd_thread_recv(nbd);
> +		error = nbd_thread_recv(nbd, bdev);
>  		nbd_dev_dbg_close(nbd);
>  		kthread_stop(thread);
>  
> -- 
> 2.1.4
> 
> 

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