block: change blk_get_meta_cap() stub return -ENOIOCTLCMD

When introduced in commit 9eb22f7 ("fs: add ioctl to query metadata
and protection info capabilities") the stub of blk_get_meta_cap() for
!BLK_DEV_INTEGRITY always returns -EOPNOTSUPP.  The motivation was that
while the command was unsupported in that configuration it was still
recognized.

A later change instead assumed -ENOIOCTLCMD as is required for unknown
ioctl commands per Documentation/driver-api/ioctl.rst. The result being
that on !BLK_DEV_INTEGRITY configs, any ioctl which reaches
blkdev_common_ioctl() will return -EOPNOTSUPP.

Change the stub to return -ENOIOCTLCMD, fixing the issue and better
matching with expectations.

[ The blkdev_common_ioctl() confusion has been fixed, but -ENOIOCTLCMD
  is the right thing to return for unrecognized ioctls, so the patch
  remains the right thing to do.   - Linus ]

Link: https://lore.kernel.org/lkml/CACzX3AsRd__fXb9=CJPTTJC494SDnYAtYrN2=+bZgMCvM6UQDg@mail.gmail.com
Fixes: 42b0ef0 ("block: fix FS_IOC_GETLBMD_CAP parsing in blkdev_common_ioctl()")
Signed-off-by: Klara Modin <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: klarasm

include/linux/blk-integrity.h

@@ -97,7 +97,7 @@ static inline struct bio_vec rq_integrity_vec(struct request *rq)
 static inline int blk_get_meta_cap(struct block_device *bdev, unsigned int cmd,
 				   struct logical_block_metadata_cap __user *argp)
 {
-	return -EOPNOTSUPP;
+	return -ENOIOCTLCMD;
 }
 static inline int blk_rq_count_integrity_sg(struct request_queue *q,
 					    struct bio *b)