Re: [PATCH] nfsd: make nfsd4_scsi_identify_device retry with a larger buffer

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, May 07, 2018 at 09:01:31AM -0400, Scott Mayhew wrote:
> nfsd4_scsi_identify_device() performs a single IDENTIFY command for the
> device identification VPD page using a small buffer.  If the reply is
> too large to fit in this buffer then the GETDEVICEINFO reply will not
> contain any info for the SCSI volume aside from the registration key.
> This can happen for example if the device has descriptors using long
> SCSI name strings.
> 
> When the initial reply from the device indicates a larger buffer is
> needed, retry once using the page length from that reply.

Looks good, but how did you choose 65532 as the maximum?  Does the scsi
layer give us any maximum?

Also, I don't know why this is bothering me, but: I'd prefer "buflen" to
"bufflen".

--b.

> 
> Signed-off-by: Scott Mayhew <smayhew@redhat.com>
> ---
>  fs/nfsd/blocklayout.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/nfsd/blocklayout.c b/fs/nfsd/blocklayout.c
> index 70b8bf7..0cd9249 100644
> --- a/fs/nfsd/blocklayout.c
> +++ b/fs/nfsd/blocklayout.c
> @@ -216,13 +216,14 @@ static int nfsd4_scsi_identify_device(struct block_device *bdev,
>  	struct request_queue *q = bdev->bd_disk->queue;
>  	struct request *rq;
>  	struct scsi_request *req;
> -	size_t bufflen = 252, len, id_len;
> +	size_t bufflen = 252, maxlen = 65532, len, id_len;
>  	u8 *buf, *d, type, assoc;
> -	int error;
> +	int retries = 1, error;
>  
>  	if (WARN_ON_ONCE(!blk_queue_scsi_passthrough(q)))
>  		return -EINVAL;
>  
> +again:
>  	buf = kzalloc(bufflen, GFP_KERNEL);
>  	if (!buf)
>  		return -ENOMEM;
> @@ -255,9 +256,16 @@ static int nfsd4_scsi_identify_device(struct block_device *bdev,
>  
>  	len = (buf[2] << 8) + buf[3] + 4;
>  	if (len > bufflen) {
> -		pr_err("pNFS: INQUIRY 0x83 response invalid (len = %zd)\n",
> -			len);
> -		goto out_put_request;
> +		if (len < maxlen && retries--) {
> +			blk_put_request(rq);
> +			kfree(buf);
> +			bufflen = len;
> +			goto again;
> +		} else {
> +			pr_err("pNFS: INQUIRY 0x83 response invalid (len = %zd)\n",
> +				len);
> +			goto out_put_request;
> +		}
>  	}
>  
>  	d = buf + 4;
> -- 
> 2.9.5