zed.d/all-debug.sh: simplify

By locking the log file itself, we can omit arduous rebinding and
explicit umask setting, but, perhaps more importantly, avoid permanently
littering /var/lock/ with zed.debug.log.lock we will never delete

It is imperative that the previous commit
("zed-functions.sh: zed_lock(): don't truncate lock")
be included in any series that contains this one

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12042

cmd/zed/zed.d/Makefile.am

@@ -52,3 +52,6 @@ install-data-hook:
 	    ln -s "$(zedexecdir)/$${f}" "$(DESTDIR)$(zedconfdir)"; \
 	done
 	chmod 0600 "$(DESTDIR)$(zedconfdir)/zed.rc"
+
+# False positive: 1>&"${ZED_FLOCK_FD}" looks suspiciously similar to a >&filename bash extension
+CHECKBASHISMS_IGNORE = -e 'should be >word 2>&1' -e '&"$${ZED_FLOCK_FD}"'

cmd/zed/zed.d/all-debug.sh

@@ -12,15 +12,11 @@
 
 zed_exit_if_ignoring_this_event
 
-lockfile="$(basename -- "${ZED_DEBUG_LOG}").lock"
+zed_lock "${ZED_DEBUG_LOG}"
+{
+	printenv | sort
+	echo
+} 1>&"${ZED_FLOCK_FD}"
+zed_unlock "${ZED_DEBUG_LOG}"
 
-umask 077
-zed_lock "${lockfile}"
-exec >> "${ZED_DEBUG_LOG}"
-
-printenv | sort
-echo
-
-exec >&-
-zed_unlock "${lockfile}"
 exit 0