patch libxo support for fstat

[ayushjayaswal.connect_gmail.com]

Summary

This Patch does the following:

+ provides --libxo flag for output and replaces all printf and fprintf calls with libxo equivalents.
+ fixes compilation warning at fstat.c:186:45
+ updates man page for fstat

[fuz]

Please adjust the indentation style as per style(9).

[ayushjayaswal.connect_gmail.com]

+ fixed indents
+ made the the xo flags compatible with https://reviews.freebsd.org/D48706 that handles kqueue, mqueue, and procdesc file descriptors

[ayushjayaswal.connect_gmail.com]

• update docs with main branch

[ayushjayaswal.connect_gmail.com]

• manual fix

[fuz]

Looks good now, but perhaps someone with more experience with libxo should have a look over D50699 and this one.

[asomers]

You need to add "LIBADD= xo" to usr.bin/fstat/Makefile. Also, a lot of fields are missing in the html output, for example file_type. Is that intentional?

usr.bin/fstat/fstat.c

193–196

This part prints out a garbled title line like this:

{T:/%-13s}{T:/%-6s}{T:/%-3s}USER         CMD   PIDFD         MOUNT

327

Here, and also for mqueue, eventfd, and procdesc, I don't think it makes sense to include the brackets in the json output. The purpose of those brackets was to tell the user that "this thing doesn't really have a mountpoint". But with any kind of machine-readable output, there's no need. Especially since it's in a field clearly labeled "file_type".

647

The json output contains an extra space in the mode. I don't think it should be there:

"inode": 4582283,
"mode": "drwxr-xr-x ",
"size": 11,

651

For device files, this prints a nonsensical size:

"vnode": {
  "mount": "/dev",
  "inode": 54,
  "mode": "crw--w---- ",
  "size": "pts/0",
  "access": {
    "access_flags": "rw"
  }