VOP_VPUT_PAIR(): handle the case when dvp == vp

[kib]

Also handle in the default implementation

[markj]

sys/ufs/ffs/ffs_vnops.c

2008–2009

Don't you also need to check here?

[jah]

Is there some situation in which we expect dvp and vp to be the same, without the caller taking steps to avoid using VOP_VPUT_PAIR() in the first place?

[kib]

In D57824#1325771, @jah wrote:

Is there some situation in which we expect dvp and vp to be the same, without the caller taking steps to avoid using VOP_VPUT_PAIR() in the first place?

I hope that no, there is no such case. I wanted to use VOP_VPUT_PAIR() in some path for the RENAME_EXCHANGE path but it requires more generic behavior.

[kib]

Handle one more return place for dvp == vp.

[markj]

sys/kern/vfs_default.c

1642–1643

What should the VOP do if unlock_vp is false and vp == dvp? Right now we're unconditionally unlocking it.

[kib]

Clean up the case dvp == vp && !unlock_vp.
Add comment to vop_stdvput_pair() explaining the intent.
Change vrele() to vunref() for locked vnode, but it should be nop since there must be one more use reference.