Implement posix_fallocate(2) by fo_fspacectl.

[khng]

Summary

fspacectl(2)'s cmd parameter supports SPACECTL_ALLOC besides
SPACECTL_DEALLOC in this commit. posix_fallocate(2) is implemented with
fo_fspacectl under the hood.

VOP_ALLOCATE(9) is expanded to have an extra flags and cred parameters.

uipc_shm and NFS client/server are converted to use the new
VOP_ALLOCATE(9) prototype.

struct fileops::fo_fallocate is eliminated.

Submitted by: Ka Ho Ng <[e-mail]>
Sponsored by: The FreeBSD Foundation

[khng]

Update commit message

[khng]

Rebased

[khng]

Rebased on top of the newest D27194.

[khng]

nfsvno_allocate: Use cred from argument instead of td_ucred.

[khng]

Rebased.

[gbe]

Two small nits from manpages.

lib/libc/sys/fspacectl.2

67

...argument within the file system space.

70

...for a non-hole region.

[khng]

Some fixes suggested by gbe@, with one more sentence explaining SPACECTL_ALLOC.

[khng]

STYLE: normalizing date format to: February 8, 2021

[gbe]

LGTM from manpages

[khng]

Rebased and fixed manpage.

[khng]

sys/fcntl.h fixes

[khng]

Moved the following into this revision:

	/* Translate to posix_fallocate(2) return value as needed. */
	if (error == ENOMEM)
		error = ENOSPC;

[khng]

manpage fixes.

[khng]

Compilation fixes after rebase