Add kqueue support for ZFS.

[pfg]

Summary

UFS and ext2fs both support kqueue(2) events for vnodes, NetBSD recently added
support for kqueue[1], which seems that is missing from FreeBSD.

Looking at UFS, it seems like the attached patch should do the trick, but I
am no expert on this.

[1]
https://github.com/NetBSD/src/commit/aabc405a6a5bfdd07c072fb9a58985ad177229f1

Test Plan

Good question.

[mav]

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c

5319

I am not familiar with this KPI, but this looks like a typo ('p' instead of 'q').

[pfg]

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c

5319

Yes it is ... now I wonder how trhis compiled!

[pfg]

Fix typo

[kib]

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c

5319

More interesting question is what is the case that did not worked before your patch but works after.

I highly suspect that these filters in UFS are just dead code. I suggest you to take a look at fifospecops.vop_kqfilter. If actually reachable, this is a panic.

[pfg]

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c

5319

fifofs is rather particular in that most fifo_specops operations are invalid:

struct vop_vector fifo_specops = {
	.vop_default =		&default_vnodeops,

	.vop_advlock =		fifo_advlock,
	.vop_close =		fifo_close,
	.vop_create =		VOP_PANIC,
	.vop_getattr =		VOP_EBADF,
	.vop_ioctl =		VOP_PANIC,
	.vop_kqfilter =		VOP_PANIC,
	.vop_link =		VOP_PANIC,
	.vop_mkdir =		VOP_PANIC,
	.vop_mknod =		VOP_PANIC,
	.vop_open =		fifo_open,
	.vop_pathconf =		VOP_PANIC,
	.vop_print =		fifo_print,
	.vop_read =		VOP_PANIC,
	.vop_readdir =		VOP_PANIC,
	.vop_readlink =		VOP_PANIC,
	.vop_reallocblks =	VOP_PANIC,
	.vop_reclaim =		VOP_NULL,
	.vop_remove =		VOP_PANIC,
	.vop_rename =		VOP_PANIC,
	.vop_rmdir =		VOP_PANIC,
	.vop_setattr =		VOP_EBADF,
	.vop_symlink =		VOP_PANIC,
	.vop_write =		VOP_PANIC,
};

[pfg]

I am starting to concur that this call may be obsoleted.
Let me add the kqueue maintainer and the fuse maintainer (Alan added kqueue support to fuse) as they may shed some more light on this

[asomers]

My experience is not directly applicable. All I did was add kqueue support for /dev/fuse, not for files stored on fusefs, and I was only concerned with EVFILT_(READ|WRITE), not EVFILT_VNODE. I would suggest that before you continue working on this patch, you write a test case.

[asomers]

Can we close this review now?

[pfg]

In D21638#531526, @asomers wrote:

Can we close this review now?

Yeah .. sorry for keeping this open for so long.