df: Make warning failures fatal

[jlduran]

Summary

Replace xo_warn() and xo_warnx() calls with xo_err() and xo_errx()
throughout the df command to ensure consistent error reporting and
proper exit codes when memory allocation or a system call fails.
This improves the reliability and behavior of the command in error
conditions.

Suggested by: des

[jlduran]

Note that we want to keep the current behavior in makenetvfslist().

[des]

In D55610#1272406, @jlduran wrote:

Note that we want to keep the current behavior in makenetvfslist().

Why?

[jlduran]

In D55610#1272421, @des wrote:

In D55610#1272406, @jlduran wrote:

Note that we want to keep the current behavior in makenetvfslist().

Why?

Actually my original statement should have been a question.
I see the code comes from a25695c3a433cd76b68427ef324efc1f109f36ed, as a result of the bug report:
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=27240
It is not clear why warnx() was preferred.
I'll update shortly.

[jlduran]

bin/df/df.c

658

I'm not a fan of this chunk of code.

[des]

bin/df/df.c

658

Well then refactor it. It was written this way to avoid duplicating the cleanup, but since you are now existing on allocation failure, that problem no longer exists.

[jlduran]

Refactor chunk of code:

• Prefer clear, separate if statements
• sizeof(char) is always 1

[des]

bin/df/df.c

658

s/existing/exiting/

[des]

bin/df/df.c

641–642

This is not needed.

645–646

This is not needed.

651–652

This is not needed.

665–666

This is not needed.

[jlduran]

Address suggestions:

• Do not manually reclaim memory