[PATCH v2] nfsd: make nfsd4_scsi_identify_device retry with a larger buffer

[Scott Mayhew <smayhew@redhat.com>]

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.

Signed-off-by: Scott Mayhew <smayhew@redhat.com>
---
 fs/nfsd/blocklayout.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

Changes since v1:
- added comment explaining the initial and max buffer lengths
- changed the len-to-maxlen comparison from "<" to "<="

diff --git a/fs/nfsd/blocklayout.c b/fs/nfsd/blocklayout.c
index 70b8bf7..aa1c6f9 100644
--- a/fs/nfsd/blocklayout.c
+++ b/fs/nfsd/blocklayout.c
@@ -216,13 +216,21 @@ 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;
+	/*
+	 * The allocation length (passed in bytes 3 and 4 of the INQUIRY
+	 * command descriptor block) specifies the number of bytes that have
+	 * been allocated for the data-in buffer.
+	 * 252 is the highest one-byte value that is a multiple of 4.
+	 * 65532 is the highest two-byte value that is a multiple of 4.
+	 */
+	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 +263,16 @@ 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