Linux 4.11 compat: iops.getattr and friends

Linux 4.11 compat: iops.getattr and friends

In torvalds/linux@a528d35, there are changes to the getattr family of functions,
struct kstat, and the interface of inode_operations .getattr.

The inode_operations .getattr and simple_getattr() interface changed to:

int (*getattr) (const struct path *, struct dentry *, struct kstat *,
    u32 request_mask, unsigned int query_flags)

The request_mask argument indicates which field(s) the caller intends to use.
Fields the caller has not specified via request_mask may be set in the returned
struct anyway, but their values may be approximate.

The query_flags argument indicates whether the filesystem must update
the attributes from the backing store.

Currently both fields are ignored.  It is possible that getattr-related
functions within zfs could be optimized based on the request_mask.

struct kstat includes new fields:
u32               result_mask;  /* What fields the user got */
u64               attributes;   /* See STATX_ATTR_* flags */
struct timespec   btime;        /* File creation time */

Fields attribute and btime are cleared; the result_mask reflects this.  These
appear to be optional based on simple_getattr() and vfs_getattr() within the
kernel, which take the same approach.

Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes #5875